Radiopharmaceutical Somatostatin Receptor Ligands and Precursors thereof

Neuroendocrine tumors (NETs) are a heterogenous group of malignancies, originating from the neuroendocrine system. This system is comprised of neuroendocrine cells in a variety of different tissues like endocrine glands (pituary, parathyroids, adrenal), pancreatic tissue or the endocrine cells located in the digestive and respiratory system (diffuse endocrine system: lungs, gastrointestinal tract) [1] NETs are a rare entity with an incidence of 2-5/100000 (0.5% of newly diagnosed malignancies per year), depending on the patients (ethnic) decent. With 67%, tumors of the gastrointestinal tract are the most common, followed by NETs in the respiratory system with 25%. Even though the incidence may be low, the number of diagnosed entities has increased over the past 30 years due to optimized methods in diagnostics [1-4]. However, somatostatin receptors (SST) expression are not restricted to neuroendocrine lung tumors, but are also a feature of some non-neuroendocrine carcinomas [5, 6]

Shortly after cloning, two classes or groups of SST receptors were identified on the basis of their phylogeny, structural homologies, and pharmacological properties: a) the first class was referred to as SRIF1 , comprising SST2, SST3, and SST5 receptor subtypes, whereas the other class was referred to as SRIF2, comprising the other two recombinant receptor subtypes SST 1 and SST4 [7] The G-protein-coupled receptors SST1-5 are expressed naturally on neuroendocrine cells of various tissues but are overexpressed on various types of NETs and other tumors and their metastases [8-10]. Therefore, the SST receptors are attractive targets for diagnostic clarification, applying e.g. positron-emission-tomography (PET) [11]. The high expression density and frequency of SST2 was found to play a dominant role for the diagnosis and therapy of cancer, resulting in the development of radiopharmaceuticals with generally high affinity towards SST2 and additional affinity of various degree to the other receptors [8, 11]. In addition, pan-ligands with high affinity to all 5 subtypes have been developed [6].

In the past decades, positron emission tomography (PET) has developed into a leading imaging method in nuclear medicine [12] In contrast to computed tomography and magnetic resonance tomography, which provides detailed anatomical and morphological information, PET provides functional information, i.e. about physiological and biochemical processes in the body before any macroscopic or morphological abnormalities or clinical signs of possible disease appear [13].

For PET diagnostics, ⁶⁸ Ga and ¹⁸ F are currently the most often used b ⁺ (positron) emitting radionuclides. For the complexation of gallium, chelators like DOTA or NOTA are available. A new methodology for introducing fluorine via an isotope exchange reaction using silicon fluoride acceptors (SiFAs) can significantly improve the accessibility of 18F-labeled ligands [14]. As a PET nuclide ⁶⁸ Ga shows some beneficial properties. Although ⁶⁸ Ga can also be produced by means of on-site cyclotrons, the broad availability of ⁶⁸ Ga is ensured by means of commercially available, easy to handle ⁶⁸ Ge/ ⁶⁸ Ga generators ( ⁶⁸ Ge; ti¾ = 270.8 d). Such generators are often expensive and typically provide up to 1.8 GBq ⁶⁸ Ga per elution. The daughter radionuclide ⁶⁸ Ga emits b ⁺ with a high abundance (89%) and a positron energy (E, _3c (b ⁺ ) = 1 -89 MeV) that allows good resolution on clinical scanners. The physical half-life of 68 min provides sufficient time for labeling, while labeling is simple and can be carried out by complexation with high radiochemical yields (RCY).

Because of its nuclear properties, ¹⁸ F has always been the PET-radionuclide of choice. Compared to ⁶⁸ Ga, ¹⁸ F has a higher positron abundance (97% b ⁺ ), a weaker 8 ⁺ -emission energy (E _ma ^ ⁺ ) = 0.64 MeV) and a longer half-life (ti _/ 2 = 109.8 min). This provides image images with better resolution, especially in combination with small animal scanners, but also on clinical scanners. Unlike ⁶⁸ Ga, the production of ¹⁸ F requires an on-site cyclotron or the daily supply with ¹⁸ F-fluoride from a cyclotron site. Modern cyclotrons allow for the production of >1 Oci (370 GBq) ¹⁸ F-fluoride, which in turn allows for the large scale production of ¹⁸ F- radiopharmaceuticals and the treatment of a large number of patients and with significantly reduced costs [12]

For the introduction of ¹⁸ F into a tracer by formation a of carbon-fluorine bond, most often a nucleophilic substitution, either aliphatic or aromatic, of a leaving group by [ ¹⁸ F]fluoride is carried out. Because of the low reactivity, an activation of the fluoride anion in anhydrous, polar aprotic solvents as well as elevated reaction temperatures is typically required. Thus, eliminations are often observed resulting in side reactions and undesired by-products, which require purification steps and lead to reduced RCY [15].

To circumvent the problems of classical nucleophilic fluorination, new methods for the formation of phosphorus-fluorine, silicon-fluorine, or boron-fluorine bonds have been developed. One promising method is the ¹⁸ F labeling of silicon fluoride acceptors by isotopic exchange reactions [16]. The focus here has been placed on silicon-fluorine compounds, which have a high stability under physiological conditions (pH 7.4 in blood plasma), but also allow a rapid isotope exchange at room temperature. The compound di-ferf-butylphenyl- fluorosilane and derivatives thereof proved to be particularly stable against defluorination in fluoride-free aqueous solution. The stability is based on a shielding effect of the two sterically demanding tert-butyl substituents that efficiently inhibit the attack of a hydroxyl group at the Si to form the pentacoordinated intermediate and finally the SN2 based OH-for-F-substitution of such compounds [14].

In contrast, the two tert-butyl-groups are not able to prevent the attack of a small fluoride anion and the following SN2 based ¹⁸ F-for- ¹⁹ F-isotopic exchange. The ¹⁹ F- ¹⁸ F isotope exchange is rapid, even at room temperature, and result in 80-90% RCY within 10 to 15 min at room temperature when ¹⁸ F-fluoride of high specific activity (> 100 GBq/pmol) is used [14]. Thus, di- tert-butylphenyl-fluorosilane and analogues thereof have been named “Silicone-Based Fluoride Acceptors” (SiFA). The first compounds with SiFA motifs for effective coupling to peptides were para-(di-tert-butylfluorosily)benzoic acid (SiFA-benzoic acid) and para-( \-tert- butylfluorosily)benzaldehyde (SiFA-benzaldehyde). The SiFA-benzaldehyde can be attached to a peptide via oxime ligation, while the SiFA-benzoic acid is converted into an active ester or activated in-situ to act as an acylation agent on an N-terminal end of a peptide or a side chain amine of a peptide to form a peptide bond [17] A recently published approach reported by Niedermoser et. at. described the development of SiFA/nTATE, a SiFA based Tyr ³ -Octreotate analogue labelled with ¹⁸ F by means of the SiFAlin aldehyde moiety [18, 19]. The above mentioned ¹⁸ F-based SST tracer [ ¹⁸ F]SiFA//nTATE has gained some interest over the last years [20, 21]. However, compared to clinically established ⁶⁸ Ga-based ligands like [ ⁶⁸ Ga]DOT A-T ATE , the overall in vivo characteristics were less favorable [19, 20, 22]

One significant drawback of oxime based SiFA-radiopharmaceuticals that are produced via aldehydes synthesized is the equilibrium between the oxime product on one hand, and the educts -the free SiFA-aldehyde or SiFA//n-alhedyde and the aminooxy-conjugated peptide- one the other hand, in aqueous solution at pH 1 .5-4.5. Consequently and not surprisingly, the dissolution of the SiFA//n precursor in a solution with oxalic acid (which is necessary to adjust the alkaline pH) prior to the isotopic exchange with preactivated [ ¹⁸ F]fluoride, has been found to result in decomposition of the precursor [23]

The invention thus provides novel SiFA-based SST receptor ligand compounds suitable for the imaging and/or treatment of neuroendocrine tumors. These SST receptor ligand compounds are comprised of: 1. a SiFA-moiety, 2. a chelator or a chelate and 3. a hydrophilic amino acid/amino acid sequence. The latter two compensate the high lipophilicity and partially binding to human serum albumin (HSA) of the SiFA-building block as relevant factors influencing in vivo parameters like blood clearance, extravasation and diffusion into tissue, such as tumor tissue, or the route of excretion, to mention the most relevant. Additionally, the amino acid/amino acid sequence modulates the overall ligand net charge, influencing the ligands affinity towards the target. Through adjustment of the SiFA-building block (e.g. addition of a positive charge) the affinity of SiFA to HSA can be lowered distinctively. All those parameters - lipophilicity, affinity to target and HSA-binding - affect the tumor uptake of such radiopharmaceuticals and therefore the diagnostic accuracy or therapeutic effect. In addition, the above described design not only allows the development of ¹⁸ F-labeled diagnostic radiopharmaceuticals, but also allows for the development of therapeutic tracers labelled at the chelator with a radiometal (such as Lu-177, Y-90 or Ac-225, to mention only a few) to form a chelate. While in such therapeutic tracers the SiFA moiety is not radioactive (...Si- ¹⁹ F), the ¹⁸ F-labelled/not radioactive chelate of a therapeutic tracer can be used for pretherapeutic dosimetry by means of PET imaging by using a tracer with exactly the same chemical structure and thus in vivo properties.

In addition, the combination of Si FA, chelator and additional hydrophilic building blocks makes it possible to modulate the pharmacokinetic properties, suited best for the imaging or therapy of SST expressing tumors. The compounds of the invention are thus particularly suitable for medical applications such as preclinical and clinical imaging, therapeutic applications, such as endoradiotherapy as well as pretherapeutic dosimetry.

In particular, the invention provides a compound of formula (I) or a salt thereof: wherein:

R ^B is a binding motif which is able to bind to a somatostatin receptor;

L ^D1 is a divalent linking group; m is an integer of 2 to 6, preferably 2 to 5, more preferably 2 or 3;

A ^H1 is, independently for each occurrence, an amino acid unit derived from a hydrophilic amino acid which comprises, in addition to its -Nhh and its -COOH functional group, a further hydrophilic functional group, and one of the m units A ^H1 may further carry a hydrophilic unit other than an amino acid bound to its hydrophilic functional group;

L ^T1 is a trivalent linking group;

R ^CH is a chelating group which optionally contains a chelated radioactive or non-radioactive cation;

R ^M1 is a hydrophilic modifying group, and p is 0 or 1; L ^D2 is a divalent linking group, and q is 0 or 1; and

R ^s is a silicon-fluoride acceptor (SiFA) group of one of the following formulae, which comprises a silicon atom and a fluorine atom, and which can be labeled with ¹⁸ F by isotopic exchange of ¹⁹ F by ¹⁸ F or which is labeled with ¹⁸ F: if p is 1 , R ^s is a group of formula (S-3) or a group of formula (S-4): wherein r is 1 , 2 or 3, preferably 1 , s in -(CH2) _S - is an integer of 1 to 6 and is preferably 1 , the groups R are, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and are more preferably both methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound; and if p is 0, R ^s is a group of formula (S-4) as defined above. As explained above, the compounds of the invention encompass compounds of formula (I). Moreover, salts, typically pharmaceutically acceptable salts, of the compounds of formula (I) are encompassed by the present invention. Thus, unless indicated to the contrary, any reference to a compound of the invention herein encompasses the compounds of formula (I) (and the preferred embodiments of these formulae disclosed herein), and the salts thereof. Likewise, any racemates, enantiomers, or diastereomers of any chiral compounds of formula (I) and their salts are encompassed, unless a specific stereochemistry of the compound under consideration is indicated in a specific context. Due to their capability of binding to a somatostatin (SST) receptor and of acting as a ligand for such a receptor, the compounds of the invention may also be referred to as SST receptor ligand compounds of the invention, or briefly as ligand compounds of the invention.

In the following a further description will be provided of the compounds of formula (I) and their salts, and of preferred embodiments thereof.

In order to be able to act as somatostatin (SST) receptor binding ligand compounds, the compounds of the invention comprise a binding motif R ^B which ensures the ligand/receptor interaction to take place between the compounds in accordance with the invention and an SST receptor and thus serves as a fundamental affinity anchor for the compounds towards the SST receptor. R ^B may also be referred to as a targeting group or a targeting motif in the compounds of the invention. Preferably, R ^B is able to bind to at least somatostatin receptor 2, or SST ₂ , or more somatostatin receptor subtypes, or even to all somatostatin receptor subtypes, the latter resulting in so called SST pan-receptor ligands.

The binding motif R ^B is capable of binding with high affinity to one or more SST receptors. In this context, high affinity binding preferably means that the ligand compound comprising the binding motif exhibits an IC50 in the low nanomolar range, preferably 50 nM or less, more preferably 10 nM or less, still more preferably 5 nM or less. For the sake of clarity, the half maximal inhibitory concentration (IC50) is defined here as the quantitative measure of the molar concentration of binding motif R ^B or a ligand compound according to formula (I) or (II) necessary to inhibit the binding of a radioactive reference ligand, here [ ¹²⁵ l]Tyr ³ -Octreotide, in vitro to SST receptors by 50%. [1]

It will be understood that a preferred binding motif which is capable of high affinity binding to an SST receptor as referred to herein may show high affinity to more than one SST receptor type. Preferably, the binding motif R ^B is one which shows the highest binding affinity among SST receptor subtypes to SST ₂ .

Suitable binding motifs include agonists and antagonists of an SST receptor.

Together with a structure which ensures a binding interaction between the compounds in accordance with the invention and an SST receptor, the binding motif R ^B generally comprises a coupling group, i.e. a functional group which allows R ^B to be attached to the remainder of the compound of the invention via a covalent bond which is formed between the group R ^B and L ^D1 or L ^T2 , respectively. The coupling group may consist of one or more atoms. Exemplary coupling groups can be selected from -NH-, -NR- (wherein the group R is C1 to C6 alkyl and is preferably methyl), -C(O)-, -0-, -S-, a quaternary ammonium group, and a thiourea bridge or a group which forms such a thiourea bridge together with a complementary group to which R ^B is attached. In this context, and also in other instances where reference is made to a quaternary ammonium group as a possible coupling group herein, the quaternary ammonium group is preferably a coupling group of the formula -N(R) ₂ ⁺ -, wherein the groups R are independently C1 to C6 alkyl, and are preferably methyl. As will be understood, a coupling group comprised by R ^B may be covalently linked to a further, complementary coupling group comprised by L ^D1 or L ^T2 in the compound in accordance with the invention, so that the two coupling groups combine to form a binding unit, such as an amide bond (-C(O)-NH-), an alkylated amide bond (-C(O)-NR-), or a thiourea bridge (-NH-C(S)-NH-). As referred to herein, also in further instances below, the substituent R in the alkylated amide bond -C(0)-NR- is C1 to C6 alkyl, preferably methyl. It is preferred that R ^B comprises a coupling group -NH-, and that the coupling group forms an amide bond -C(0)-NH- with a group -C(O)- provided by L ^D1 or L ^T2 , respectively.

Typically, the binding motif R ^B comprises a peptide structure, preferably a cyclic peptide structure or a peptide cyclized by a disulfide bridge, capable of binding to an SST. Diverse peptides capable of binding to an SST are known and described in the literature. They can be used to provide the binding motif in a compound of the invention, e.g. by forming an amide bond with the remainder of the compound using a carboxylic acid group or an amino group contained in the peptide.

Thus, the binding motif may comprise a group, and preferably is a group, which can be derived from a receptor agonist or receptor antagonist selected from Tyr ³ -Octreotate (or Tyr ³ Thr ⁸ - Octreotide, TATE, H-D-Phe-cyc/o(L-Cys-L-Tyr-D-Trp-L-Lys-L-Thr-L-Cys)-L-Thr-OH) , Thr ⁸ - Octreotide (ATE), Phe ¹ ,Tyr ³ -Octreotide (TOC, H-D-Phe-cyc/o(L-Cys-L-Tyr-D-Trp-L-Lys-L-Thr- L-Cys)-L-Thr-ol), Nal ³ -Octreotide (NOC, H-D-Phe-cyc/o(L-Cys-L-1-Nal-D-Trp-L-Lys-L-Thr-L- Cys)-L-Thr-ol), l-NaP.Thi^-Octreotide (NOCATE), BzThi ³ -Octreotide (BOC), BzThP.Thr ⁸ - Octreotide (BOCATE), JR11 (H-L-Cpa-cyc/o(D-Cys-L-Aph(Hor)-D-Aph(Cbm)-L-Lys-L-Thr-L- Cys)-D-Tyr-NH ₂ ), BASS (H-L-Phe(4-N0 ₂ )-cyc/o(D-Cys-L-Tyr-D-Trp-L-Lys-L-Thr-L-Cys)-D- Tyr-NH ₂ ) and KE121 (cyc/o(D-Dab-L-Arg-L-Phe-L-Phe-D-Trp-L-Lys-L-Thr-L-Phe)), more preferably from TATE or JR11 , and most preferably from TATE. As will be understood by the skilled reader, the group R ^B can be conveniently derived from the receptor agonists or antagonists listed above by using a functional group, such as a carboxylic acid group or an amino group, contained in the receptor agonist or antagonist, to provide a coupling group which attaches the group R ^B to the remainder of the compound. Preferably, these peptidic receptor agonists or receptor antagonists provide the group R ^B by using an amino group contained therein, e.g. in an optionally substituted phenylalanine unit contained in the peptide, to form an amide bond with the remainder of the compound of the invention. In this case, the covalent bond between R ^B and L ^D1 (formula (I)), is formed between a terminal -NH- group as a coupling group in R ^B and a terminal -C(O)- group that may be present as a terminal coupling group in L ^D1 .

Alternatively, as will be understood by the skilled reader, the group R ^B can be conveniently derived from the receptor agonist or receptor antagonist listed above by the introduction of an additional functional moiety which provides a functional group that allows a chemical bond to be formed with L ^D1 , such as a moiety with an isothiocyanate that can link to an amine on L ^D1 to form a thiourea bridge. As will be understood by the skilled reader, other conjugation strategies, typically summarized as “bioconjugation strategies” can also be used to link a group R ^B in a compound in accordance with the invention to L ^D1 . In line with the above, the binding motif R ^B may comprise e.g. a group of the formula (B-1 ) or of the formula (B-2), and preferably is a group of the formula (B-1) or of the formula (B-2) as shown in the following. Among them, the group of the formula (B-1 ) if preferred.

The group of the formula (B-1 ) has the following structure: wherein the dashed line marks a bond which attaches the group to the remainder of the compound. As will be understood by the skilled reader, the bond marked by the dashed line in formula (B-1) does not carry a methyl group at its end opposite to the nitrogen atom, but represents a bond which attaches the group R ^B to the remainder of the compound of formula (I), i.e. in this case to the point of attachment of R ^B in formula (I). Preferably, the bond marked by the dashed line in formula (B-1) represents a covalent bond which is present in the compounds of the invention between the nitrogen atom of the -NH- group indicated in formula (B-1 ) and a carbon atom of a carbonyl group which may be present as a terminal group in L ^D1 . Thus, an amide bond is provided.

The group of the formula (B-2) has the following structure: wherein the dashed line marks a bond which attaches the group to the remainder of the compound. As will be understood by the skilled reader, the bond marked by the dashed line in formula (B-2) does not carry a methyl group at its end opposite to the nitrogen atom, but represents a bond which attaches the group R ^B to the remainder of the compound of formula (I), i.e. in this case to the point of attachment of R ^B in formula (I). Preferably, the bond marked by the dashed line in formula (B-2) represents a covalent bond which is present in the compounds of the invention between the nitrogen atom of the -NH- group indicated in formula (B-2) and a carbon atom of a carbonyl group which may be present as a terminal group in L ^D1 . Thus, an amide bond is provided.

More preferably, the binding motif R ^B is a group of the formula (B-1 a) or (B-2a), among which the group of the formula (B-1 a) is preferred:

wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

The chelating group R ^CH in the compounds of formula (I) and their salts is suitable to form a chelate with a radioactive or non-radioactive cation. Diverse chelating agents from which suitable chelating groups can be derived are well known in the art and can be used in the context of the present invention. Metal- or cation-chelating agents, e.g. macrocyclic or acyclic compounds, which are suitable to act as a chelating group, are available from a number of manufacturers. It will be understood that numerous chelating agents can be used in an off-the- shelf manner by a skilled person without further ado. It will further be understood that the suitability of the chelating group to form a chelate with a given cation requires the chelating group to be able to provide a chelated ligand in a chelate complex comprising the cation under consideration, but does not require the chelating group to provide the only ligand of the cation in the chelate complex. Thus, if the chelating group R ^CH contains a chelated radioactive or nonradioactive cation, the cation may be a complex cation, e.g. a metal ion carrying an additional coordinated ligand other than the chelating group, such as an oxo ligand. For example, the chelating group R ^CH may comprise at least one of

(i) a macrocyclic ring structure with 8 to 20 ring atoms of which 2 or more, preferably 3 or more, are selected from oxygen atoms and nitrogen atoms; and

(ii) an acyclic, open chain chelating structure with 8 to 20 main chain atoms of which 2 or more, preferably 3 or more are heteroatoms selected from oxygen atoms and nitrogen atoms.

Preferably, the chelating group R ^CH is a chelating group which is suitable to form a chelate comprising a cation selected from cations of Sc, Cr, Mn, Co, Fe, Ni, Cu, Ga, Zr, Y, Tc, Ru, Rh, Pd, Ag, In, Sn, Te, Pr, Nd, Gd, Pm, Tb, Sm, Eu, Gd, Tb, Ho, Dy, Er, Yb, Tm, Lu, Re, W, Pt, Ir, Hg, Au, Pb, At, Bi, Ra, Ac, and Th, or a chelate comprising a cationic molecule comprising ¹⁸ F or ¹⁹ F, such as ¹⁸ F-[AIF] ²⁺ . More preferably, the chelating group is suitable to form a chelate comprising a cation selected from a cation of Cu, Ga, Lu and Pb, and still more preferably a cation of Ga or Lu.

Together with a structure which is suitable as a chelating ligand for a cation, the chelating group R ^CH generally comprises a coupling group which allows R ^CH to be attached to the remainder of the compound of the invention via a covalent bond which is formed between the group R ^CH and L ^T1 . The coupling group may consist of one or more atoms. An exemplary coupling group can be selected from -NH-, -NR- (wherein the group R is C1 to C6 alkyl and is preferably methyl), -C(O)-, -S-, -0-, a quaternary ammonium group, and a thiourea bridge or a group which forms such a thiourea bridge together with a complementary group to which R ^CH is attached. The coupling group may be covalently linked to a further, complementary coupling group comprised in L ^T1 in the compound of the invention, so that the two coupling groups combine to form a binding unit, such as an amide bond -C(0)-NH-, an alkylated amide bond -C(0)-NR-, or a thiourea bridge. It is preferred that R ^CH comprises a coupling group - C(O)-, and that the coupling group forms an amide bond -C(0)-NH- with a group -NH- provided by L ^T1 .

The chelating group R ^CH may comprise a group, preferably is a group, which can be derived from a chelating agent selected from diethylenetriaminepentamethylenephosphonic acid (EDTMP) and its derivatives, diethylenetriaminepentaacetic acid (DTPA) and its derivatives, bis(carboxymethyl)- 1 ,4,8,11 -tetraaza-bicyclo[6.6.2] hexadecane (CBTE2a), cyclohexyl-1 ,2-diaminetetraacetic acid (CDTA), 4-(1 ,4,8,11-tetraazacyclotetradec-1-yl)-methylbenzoic acid (CPTA), N'-[5- [acetyl(hydroxy)amino] ^“ ’pentyl]-N-[5-[[4-[5-aminopentyl-(hydroxy)amino]-4-o xobutanoyl]- amino]pentyl]-N-hydroxybutandiamide (DFO) and derivatives thereof, 1 ,4,7,10- tetraazacyclododecane-1 ,7-diacetic acid (D02A), 1 ,4,7,10-tetraazacyclododecan-N,N',N",N"'- tetraacetic acid (DOTA), 2-[1 ,4,7,10-tetraazacyc!ododecane-4,7,10-triacetic acid]- pentanedioic acid (DOTAGA or DOTA-GA), 1 ,4,7,10-tetrakis(carbamoylmethyl)-1 ,4,7,10- tetraazacyclododecane (DOTAM), N,N'-dipyridoxylethylendiamine-N,N'-diacetate-5,5'- bis(phosphat) (DPDP), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine-N,N'- tetraacetic acid (EDTA), ethyleneglykol-0,0-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), N,N-bis(hydroxybenzyl)-ethylenediamine-N,N'-diacetic acid (HBED), hydroxyethyldiaminetriacetic acid (HEDTA), 1 -(p-nitrobenzyl)-l , 4,7,10-tetraazacyclodecan-

4.7.10-triacetate (HP-DOA3), 6-hydrazinyl-N-methylpyridine-3-carboxamide (HYNIC), 1 ,4,7- triazacyclononan-1 -succinic acid-4, 7-diacetic acid (NODASA), 1-(1-carboxy-3-carboxypropyl)-

4.7-(carboxy)-1,4,7-triazacyclononane (NODAGA), 1,4,7-triazacyclononanetriacetic acid

(NOTA), 4, 11 -bis(carboxymethyl)-1 ,4,8,11 -tetraazabicyclo[6.6.2]hexadecane (TE2A), 1 ,4,8,11-tetraazacyclododecane-1 ,4,8,11-tetraacetic acid (TETA), terpyridine- bis(methyleneamine) tetraacetic acid (TMT), 1 ,4,7,10-tetraazacyclotridecan-N,N',N",N"'- tetraacetic acid (TRITA), and triethylenetetraaminehexaacetic acid (TTHA), N,N'-bis[(6- ca rboxy-2-pyrid i I )methy l]-4, 13-d iaza- 18-crown-6 (H ₂ macropa), 4-amino-4-{2-[(3-hydroxy-1 ,6- dimethyl-4-oxo-1 ,4-dihydro-pyridin-2-ylmethyl)-carbamoyl]-ethyl} heptanedioic acid bis-[(3- hydroxy-1 ,6-dimethyl-4-oxo-1 , 4-d i hyd ro-pyrid i n-2-y I methyl )-a m ide] (THP), 1 ,4,7- triazacyclononane-1 ,4,7-tris[methylene(2-carboxyethyl)phosphinic acid (TRAP), 2-(4,7,10- tris(2-amino-2-oxoethyl)-1 ,4,7,10-tetraazacyclododecan-1-yl)acetic acid (D03AM), and

1.4.7.10-tetraazacyclododecane-1 ,4,7, 10-tetrakis[methylene(2-carboxyethylphosphinic acid)] (DOTPI), S-2-(4-isothiocyanatobenzyl)-1 ,4,7,10-tetraazacyclododecane tetraacetic acid, hydrazinonicotinic acid (HYNIC), 6-amino-6-methylperhydro-1,4-diazepine-N,N,N',N'- tetraacetic acid (AAZTA) and derivatives thereof, such as (6-pentanoic acid)-6-(amino)methyl- 1 ,4-diazepine triacetate (DATA), pentadeca-1 ,4,7,10, 13-penta-aminopentaacetic acid (PEPA), hexadeca-1 ,4,7,10,13,16-hexaamine-hexaacetic acid (HEHR), 4-{[bis(phosphonomethyl)) carbamoyl] methyl}-7,10-bis(carboxymethyl)-1 ,4,7,10-tetraazacyclododec-1-yl) acetic acid (BPAMD), N-(4-{[bis (phosphonomethyl)) carbamoyl] methyl}-7,10-bis (carboxymethyl)-nona-

1.4.7-triamine triacetic acid (BPAM), 1 ,2-[{6- (carboxylate) pyridin-2-yl} methylamine] ethane (DEDPA, H2DEDPA), deferoxamine (DFO) and its derivatives, deferiprone, (4-acetylamino-4- yl) {2-[(3-hydroxy-1 ,6-dimethyl-4-oxo-1 ,4-dihydro-pyridin-2-ylmethyl)-carbamoyl]-ethyl}- heptanedioic acid bis-[(3-hydroxy-1 ,6 -dimethyl-4-oxo-1 ,4-dihydro-pyridin-2-ylmethyl)-amide] (CP256) and its derivatives such as YM103; tetraazycyclodecane-phosphinic acid (TEAP), 6- amino-6-methylperhydro-1 ,4-diazepine-N,N,N',N'-tetraacetic acid (AAZTA); 1-N-(4- aminobenzyl) -3,6,10,13,16,19-hexaazabicyclo [6.6.6]-eicosane-1 , 8-diamine (SarAr), 6,6'-[{9- hydroxy-1, 5-bis-(methoxycarbonyl)-2,4-di(pyridin-2-yl)-3,7-diazabicycl o[3.3.1]nonane-3, 7- diyl}bis(methylene)]dipicolinic acid (h^bispa ² ), 1 ,2-[{6-(carboxylato)pyridin-2-yl}methylamino]- ethane (H2dedpa), N,N'-bis(6-carboxy-2-pyridylmethyl)-ethylenediamine-N,N'-dia cetic acid (hUoctapa), N,N'-bis(2-hydroxy-5-sulfonylbenzyl)-N,N'-bis-(2-methylpyrid yl)ethylenediamine (HeSbbpen) and derivatives thereof, triethylenetetramine-N, N , N', N" , N'", N'"-hexaacetic (TTHA), 2-aminomethylpiperidine triacetic acid (2-AMPTA) and derivatives thereof, such as 2- (N-(2-Hydroxybenzyl)aminomethyl)piperidine (2-AMPTA-HB) further functionalized derivative of 2-AMPTA with additional functional groups suitable for conjugation to peptidic structures, 4- nitro-2-hydroxybenzyl-2-{[(6)-trans-2-[benzyl(carboxymethyl) amino]cyclohexyl] (carboxymethyl)amino}acetic acid (RESCA) and derivatives thereof, and 6-carboxy-1 ,4,8,11- tetraazaundecane (N ₄ ) and derivatives thereof. Among these chelating agents, preference is given to CBTE2a, DOTA, DOTAGA, DOTAM, NODASA, NODAGA, NOTA, TE2A, D03AM, SarAr, 2-AMPTA, 2-AMPTA-HB and RESCA. More preferred are DOTA, DOTAGA, DOTAM, D03AM, NOTA and NODAGA. Still more preferred are DOTA, DOTAGA and DOTAM. In line with the general definition provided above, the chelating group derived from the exemplary chelating agents listed above optionally contains a chelated radioactive or non-radioactive cation.

As will be understood by the skilled reader, a chelating group in a compound in accordance with the invention can be conveniently derived from the chelating agents listed above by either using a functional group contained in the chelating agent, such as a carboxylic acid group, an amide group, an amino group, a hydroxy group, or a thiol function to provide a coupling group, e.g. selected from -C(O)-, -NH-, -S- and -0-, which attaches the chelating group to the remainder of the compound. Preferably, a carboxylic acid group is used to provide a coupling group -C(O)- (a carbonyl) to form an amide. The coupling group provided by R ^CH may be covalently linked to a further, complementary coupling group comprised in L ^T1 , respectively, so that the two coupling groups combine to form a binding unit, such as an amide bond -C(O)- NH-. As noted above, it is preferred that R ^CH comprises a coupling group -C(O)-, and that the coupling group forms an amide bond with a group -NH- provided by L ^T1 .

Alternatively, as will be understood by the skilled reader, a chelating group in a compound in accordance with the invention can be conveniently derived from the chelating agents listed above by the introduction of an additional functional group or the introduction of additional groups having a functional group able to form a chemical bond to L ^T1 , such as a chelator modified with an additional residue with an isothiocyanate that can link to an amine on L ^T1 by means of a thiourea bridge. As will be understood by the skilled reader, other conjugation strategies, typically summarized as “bioconjugation strategies” can also be used to link a chelating group in a compound in accordance with the invention to L ^T1 .

It is particularly preferred that R ^CH is a group of the formula (CH-1), (CH-2) or (CH-3), or a chelate formed by a group of the formula (CH-1 ), (CH-2) or (CH-3) and a chelated radioactive or non-radioactive cation, i.e. the group of the formula (CH-1 ), (CH-2) or (CH-3) optionally contains a chelated radioactive or non-radioactive cation: wherein the dashed line marks a bond which attaches the group to the remainder of the compound. As will be understood by the skilled reader, the bond at the carbonyl group marked by the dashed line in formulae (CH-1) to (CH-3) thus does not carry a methyl group at its end opposite to the carbonyl group, but represents a bond which attaches the group R ^CH to the remainder of the compound of formula (I), i.e. in this case to the point of attachment of R ^CH in formula (I). Preferably, the bond marked by the dashed line in formulae (CH-1 ) to (CH-3) represents a covalent bond which is present in the compounds of the invention between the carbon atom of the carbonyl group indicated in in formulae (CH-1 ) to (CH-3) and a nitrogen atom of an NH group which may be present as a terminal group in L ^T1 . Thus, an amide bond is provided. The chelated radioactive or non-radioactive cation that may be contained in the chelating group R ^CH preferably comprises or consists of a cation selected from cations of ⁴³ Sc, ⁴⁴ Sc, ⁴⁷ Sc, ⁵¹ Cr ¹⁵⁷ Dy, ¹⁶⁵ Dy, ¹⁶⁶ Dy, ¹⁶⁰ Er, ¹⁶⁵ Er, ¹⁶⁹ Er, ¹⁷¹ Er, ¹⁶⁶ Yb, ¹⁶⁹ Yb, ¹⁷⁵ Yb, ¹⁶⁷ Tm, ¹⁷² Tm, ¹⁷⁷ Lu, ¹⁸⁶ Re, ¹⁸⁶⁹ Re

²²⁵ Ac, ²²⁶ Th and ²²⁷ Th, and from nonradioactive isotopes of any of these metals, or is a cationic molecule comprising ¹⁸ F or ¹⁹ F, such as ¹⁸ F-[AIF] ²⁺ . The chelated cation may be a complex cation, e.g. a metal ion carrying an additional coordinated ligand other than the chelating group, such as an oxo-ligand in a chelate including a ^99m Tc(V)-oxo core.

Particularly preferred as a chelated cation is a radioactive or non-radioactive cation of Ga, Lu or Pb, such as ¹⁷⁷ Lu or ⁶⁸ Ga. Moreover, the compounds in accordance with the invention comprise a silicon-fluoride acceptor (SiFA) group R ^s which comprises a silicon atom and a fluorine atom and which can be labeled with ¹⁸ F by isotopic exchange of ¹⁹ F by ¹⁸ F or which is labeled with ¹⁸ F.

If the variable p in formula (I) is 1 , i.e. if the compound of formula (I) or its salt comprises a group R ^M \ R ^s is a group of formula (S-3) or a group of formula (S-4): In the group of formula (S-3), R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert- butyl, and more preferably R ^1S and R ^2S are tert-butyl. The dashed line marks a bond which attaches the group to the remainder of the compound.

In the group of formula (S-4), r is 1 , 2 or 3, preferably 1 , s in -(CH2) _S - is an integer of 1 to 6 and is preferably 1 , the groups R are, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and are more preferably both methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl. The dashed line marks a bond which attaches the group to the remainder of the compound.

If the variable p in formula (I) is 0, i.e. if the compound of formula (I) or its salt does not comprise a group R ^M1 , R ^s is a group of formula (S-4) as defined above.

Exemplary counterions for the positively charged quaternary ammonium group indicated in formula (S-4) which carries two substituents R are anions as they are discussed herein with regard to salts forms of the compound of formula (I), which include, e.g., trifluoro acetate anions or acetate anions.

As will be understood by the skilled reader, the bond marked by the dashed line in formulae (S-3) and (S-4) does not carry a methyl group at its end opposite to the carbonyl group, but represents a bond which attaches the SiFA group to the remainder of the compound of formula (I), i.e. in this case to the point of attachment of R ^s in formula (I). Preferably, the bond marked by the dashed line in formulae (S-3) and (S-4) represents a covalent bond which is present in the compounds of the invention between the carbon atom of the carbonyl group indicated in formulae (S-3) and (S-4) and a nitrogen atom of an -NH group which may be present as a terminal group in the unit carrying R ^s (i.e. L ^T1 , R ^M1 or L ^D2 in formula (I)). Thus, an amide bond is provided.

The fluorine atom indicated in formulae (S-3) and (S-4) may be a ¹⁸ F atom, or a ¹⁹ F atom which can be exchanged to provide ¹⁸ F by isotopic exchange of ¹⁹ F by ¹⁸ F.

Among the groups (S-3) and (S-4), most preferred as a group R ^s is the group (S-4). Furthermore, the group (S-3) is preferably a group (S-3a), and the group (S-4) is preferably a group (S-4a): wherein ‘Bu indicates a tert-butyl group and the dashed line marks a bond which attaches the group to the remainder of the compound. As noted above with respect to (S-4), exemplary counterions for the positively charged quaternary ammonium group indicated in formula (S-4a) which carries two methyl substituents are anions as they are discussed herein with regard to salts forms of the compound of formula (I), which include, e.g., trifluoro acetate anions or acetate anions.

It will be understood that the above explanations regarding the SiFA group of formulae (S-3) and (S-3a) and (S-4) and (S-4a), respectively, not only apply for formula (I), but also for the preferred embodiments thereof, wherein the SiFA groups R ^S1 , R ^S2 or R ^S3 define a group of formula (S-3) and preferably (S-3a), a group formula (S-4) and preferably (S-4a), or both.

The scaffold structure carrying the groups R ^B , R ^CH and R ^s in formula (I) as shown below comprises one or more amino acid units. As will be understood by the skilled person, an amino acid unit is a group which can be derived from an amino acid, i.e. from a compound comprising an amino group and a carboxylic acid group in the same molecule. Unless indicated otherwise in a specific context, one or more further functional groups in addition to the amino group and the carboxylic acid group may be present in the amino acid from which the amino acid unit can be derived. A specific amino acid unit is typically identified by the name of the amino acid from which it can be derived, e.g. as a glycine unit, asparagine unit, etc. Unless indicated otherwise in a specific context, the amino acids from which the amino acid units can be derived are preferably oc-amino acids. If an amino acid unit comprised in the scaffold structures can be derived from a chiral amino acid, preference is given to the D-configuration.

As will be further understood, an amino acid unit can be derived from an amino acid by using one or more of its functional groups to provide a coupling group which forms a bond to an adjacent atom or group to which the amino acid unit is attached. For example, an amino group of the amino acid may be used to provide a coupling group -NH- wherein the bond to one hydrogen atom is replaced by a bond to another adjacent atom or group. A carboxylic acid group of the amino acid may be used to provide a coupling group -C(O)- wherein the bond to the -OH group is replaced by a bond to another adjacent atom or group. Preferably, any coupling group provided by the amino acid is covalently linked to a further, complementary coupling group in the compound in accordance with the invention, so that the two complementary coupling groups combine to form a binding unit, such as an amide bond (-C(O)- NH-) or an alkylated amide bond -C(0)-NR-, preferably an amide bond. R is C1 to C6 alkyl, preferably methyl. If the amino acid providing the amino acid unit comprises a further functional group which is different from an amino or a carboxylic acid group, a coupling group different from a -NH- and a -C(O)- coupling group may be provided, e.g. -O- or -S-.

If the amino acid unit is a monovalent unit, it is preferred that the unit is attached in the compound of the invention with one amide bond formed using either an amino group or a carboxylic acid group provided by the amino acid from which the amino acid unit is derived. If the amino acid unit is a divalent unit, it is preferred that the unit is attached in the compound of the invention with two amide bonds formed using an amino group and a carboxylic acid group provided by the amino acid from which the amino acid unit is derived. If the amino acid unit is a trivalent unit, as it can be provided by an amino acid comprising a further functional group in addition to the amino group and the carboxylic acid group required for an amino acid, it is preferred that the further functional group is also an amino or a carboxylic acid group, and that the unit is attached in the compound of the invention with three amide bonds formed using an amino group, a carboxylic acid group and the further functional group provided by the amino acid from which the amino acid unit is derived.

In the following, the structural elements of the scaffold structure carrying R ^B , R ^CH and R ^s in formula (I) shall be further discussed.

The divalent linking group L ^D1 provides a link between the group R ^B and the amino acid units A ^H1 . Thus, L ^D1 typically contains a coupling group at its terminus to which R ^B is attached which is suitable to form a binding unit, such as an amide bond (-C(O)-NH-), an alkylated amide bond -C(0)-NR-, or a thiourea bridge, preferably an amide bond, with a complementary group contained in R ^B . Reference is made to the discussion of coupling groups in the context of the definition of R ^B above. Preferably, this coupling group in L ^D1 is a group -C(O)-. Likewise, L ^D1 typically contains a coupling group at its terminus to which the amino acid units A ^H1 are attached which is suitable to form a binding unit, such as an amide bond or an alkylated amide bond, preferably an amide bond, with a complementary group contained in A ^H1 . Preferably, this coupling group in L ^D1 is a group -NH-.

In one preferred embodiment, L ^D1 comprises, typically in addition to the coupling groups referred to above, a divalent oligo- or polyethylene glycol group; preferably a divalent oligo- or polyethylene glycol group having 10 or less ethylene glycol units, and more preferably a divalent oligo- or polyethylene glycol group having 2 to 5 ethylene glycol units.

In accordance with this embodiment, L ^D1 can be a divalent group of formula (L-1a):

-C(0)-(CH2)a-(0-CH2-CH ₂ )b-NH- (L-1 a) wherein a is 1 or 2, preferably 1 ; and b is an integer of 2 to 5, preferably 2 or 3.

The bond at the C-terminus of the above formula is preferably formed with R ^B . In another, more preferred embodiment, the divalent linking group L ^D1 comprises a divalent amino acid unit or a divalent chain of amino acid units, more preferably a divalent chain of 2 to 5 amino acid units, still more preferably a divalent chain of 2 or 3 amino acid units. Due to the functional groups contained in an amino acid, the amino acid unit/chain of amino acid can also provide the coupling groups discussed above for attachment of R ^B or A ^H1 . Thus, the divalent linking group L ^D1 can consist of a divalent amino acid unit or a divalent chain of amino acid units, more preferably a divalent chain of 2 to 5 amino acid units, still more preferably a divalent chain of 2 or 3 amino acid units.

In accordance with this embodiment, L ^D1 can be represented by formula (L-1b):

-[A ^L1 ]n- (L-1b) wherein

A ^L1 is, independently for each occurrence if n is more than 1 , an amino acid unit; and n is an integer of 1 to 5, preferably 2 to 5, more preferably 2 or 3.

Preferably, the group (L-1 b) provides a C-terminus which forms a bond with R ^B , and an N- terminus which forms a bond with A ^H1 .

If L ^D1 comprises or consists of one or more amino acid units, it is preferred that these amino acid units do not contain any free amino groups, free acid groups, or salts thereof. It is more preferred that the amino acid units do not contain any functional group which carries a charge at a pH of 7.0. For example, an amino acid unit comprised by L ^D1 can be selected, independently, from an amino acid unit provided by glycine, b -alanine, or y-aminobutyric acid and from an amino acid unit comprising a side chain selected from a C1-C4 alkyl group such as methyl, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _v -C(=0)NH ₂ , -(CH ₂ ) _v -NH-C(=0)-NH ₂ , and -(CH ₂ ) _V -OH, wherein v is 1 to 4, e.g. 1 or 2.

If L ^D1 comprises or consists of one or more amino acid units, it is more preferred that each amino acid unit in L ^D1 is selected, independently for each occurrence if more than one amino acid unit is present in L ^D1 , from a glycine (Gly) unit, b-alanine unit, alanine (Ala) unit, asparagine (Asn) unit, glutamine (Gin) unit, and a citrulline (Cit) unit. Still more preferred are amino acid units selected from a glycine unit and an asparagine unit. With respect to their stereochemistry, the amino acid units, except for the glycine unit, are preferably D-amino acid units. Thus, for example, a preferred group -[A ^L1 ] _n - may consist of (i) one Gly unit, (ii) two Gly units, (iii) three Gly units, or (iv) two D-Asn units, and a particularly preferred example is a group -[A ^L1 ] _n - consisting of two or three Gly units.

The variable m is an integer of 2 to 6, preferably 2 to 5, more preferably 2 or 3.

A ^H1 is, independently for each occurrence, an amino acid unit derived from a hydrophilic amino acid which comprises, in addition to its -NH2 and its -COOH functional group, a further hydrophilic functional group. Such a unit may be briefly referred to herein as “hydrophilic amino acid unit”. One of the m units A ^H1 may optionally further carry a hydrophilic unit other than an amino acid bound to its hydrophilic functional group.

For example, the further hydrophilic functional group of the amino acid units A ^H1 can be selected, independently for each occurrence, from -NH2, -COOH, -NH-C(=NH)- NH _2I -C(=0)NH ₂ , -NH-C(=0)-NH ₂ , -OH and -P(=0)(0H) ₂ . Among these, preferred are -NH ₂ , -COOH, -NH-C(=NH)-NH ₂ , -C(=0)NH ₂ , and -NH-C(=0)-NH ₂ .

Preferably, each of the m amino acid unit(s) A ^H1 comprises, independently for each occurrence if m is more than 1 , a side chain having a terminal hydrophilic functional group which side chain is selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)- NH _2I -(CH ₂ )V-C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _V -OH and -(CH ₂ ) _V -P(=0)(0H) ₂ wherein v is 1 to 4, and wherein the terminal functional group of the above side chain in one of the m units A ^H1 may form a bond with an additional hydrophilic unit other than an amino acid unit. In line with the above, the side chain is more preferably selected from -(CH ₂ ) _V - NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , and -(CH ₂ ) _v -NH-C(=0)-NH ₂ , wherein v is 1 to 4. As will be understood by the skilled reader, the side chain of the amino acid unit A ^H1 is not involved in a bond to L ^D1 , L ^T1 or to an adjacent unit A ^H1 . In line with the above, one of the m units A ^H1 may optionally further carry a hydrophilic unit other than an amino acid bound to the terminal hydrophilic functional group of the side chain.

Thus, it is preferred that the amino acid unit(s) A ^H1 is (are) selected, independently for each occurrence, from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, citrulline (Cit) unit, thiocitrullin unit, methylisothiocitrulline unit, canavanin unit, thiocanavanin unit, a-amino-y- (thioureaoxy)-n-butyric acid unit, a-amino-y-(thioureathia)-n-butyric acid unit, and a phosphonomethylalanine (Pma) unit. They are preferably units which can be derived from amino acids in D-configuration. More preferred are units selected from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, a citrulline (Cit) unit and a phosphonomethylalanine (Pma) unit. Still more preferred are units selected from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, and a citrulline (Cit) unit. Thus, in line with the above, it is particularly preferred if the group [A ^H1 ] _m consists of 2 or 3 amino acid units independently selected from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, and a glutamine (Gin) unit. For example, a preferred group [A ^H1 ] _m may consist of (i) two D-Asp units, (ii) two D-Orn units, (iii) two D-Asn units, or (iv) two D-Asp units and a third unit selected from D-Lys, D-Cit and D-Glu.

One of the units A ^H1 which are selected accordingly may optionally further carry a hydrophilic unit other than an amino acid bound to the terminal hydrophilic functional group that is provided in these amino acid units. The optional hydrophilic unit other than an amino acid unit which is optionally bound to one of the units A ^H1 can be, for example, a carbohydrate group or a trimesic acid group.

Preferably, the group -[A ^H1 ] _m - forms an amide bond (-C(O)-NH-) or an alkylated amide bond (-C(O)-NR-) with L ^D1 , and an amide bond or an alkylated amide bond with L ^T1 . More preferably, the bonds are amide bonds.

Preferably, the group -[A ^H1 ] _m - provides a C-terminus which forms a bond with L ^D1 , and an N- terminus which forms a bond with L ^T1 .

The trivalent linking group L ^T1 provides a link between the amino acid unit(s) A ^H1 , R ^CH and, depending on p and q, R ^M1 , L ^D2 or R ^s . Thus, L ^T1 typically contains a coupling group at its terminus to which A ^H1 is (are) attached, which is suitable to form a binding unit, such as an amide bond (-C(O)-NH-) or an alkylated amide bond (-C(O)-NR-), preferably an amide bond, with a complementary group contained in A ^H1 . Preferably, this coupling group in L ^T1 is a group -C(O)-. Likewise, L ^T1 typically contains a coupling group, eitherat its terminus or in a side chain, to which R ^CH is attached which is suitable to form a binding unit, such as an amide bond, an alkylated amide bond (-C(O)-NR-), or a thiourea bridge, preferably an amide bond, with a complementary group contained in R ^CH . Reference is made to the discussion of coupling groups in the above definition of R ^CH . Preferably, this coupling group in L ^T1 is a group -NH-.

At the terminus to which R ^M1 , L ^D2 or R ^s is attached, L ^T1 typically contains a coupling group selected from the following (i) and (ii), with (i) being preferred.

(i) A coupling group which is suitable to form a binding unit, such as an amide bond, an alkylated amide bond (-C(O)-NR-), or a thiourea bridge, preferably an amide bond, with a complementary group contained in R ^M1 , L ^D2 or R ^s . Reference is made to the discussion of coupling groups in the above definition of R ^s . Preferably, this coupling group in L ^T1 is also a group -NH-, which is typically derived from an amino group.

(ii) A quaternary ammonium group as a coupling group. As noted above, the quaternary ammonium group is preferably a coupling group of the formula -N(R) ₂ ⁺ ~, wherein the groups R are independently C1 to C6 alkyl, and are preferably methyl. This option can be suitably used, e.g., if both p and q are 0 and R ^s is directly attached to L ^T1 , for example if R ^s is a group (S-5) as discussed above and provides a substituent attached to the nitrogen atom of the quaternary ammonium group.

It is preferred that L ^T1 is a trivalent amino acid unit. More preferably L ^T1 is a trivalent amino acid unit selected from the following (i) and (ii), with (i) being further preferred.

(i) A trivalent amino acid unit which can be derived from an amino acid comprising, together with the carboxylic acid group and the amino group, a further functional group selected form a carboxylic acid group and an amino group. More preferably, L ^T1 is selected from a 2,3- diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit, most preferably a Dap unit. With respect to their stereochemistry, these amino acid units are preferably D-amino acid units.

(ii) A trivalent amino acid unit comprising a -N(R)2 ⁺ - group which unit can be derived from a trifunctional amino acid comprising a tertiary amino group as a third functional group in addition to its -NH ₂ group and its -COOH group, preferably an amino acid selected from N- dialkylated 2,3-diaminopropionic acid (Dap), N-dialkylated 2,4-diaminobutanoic acid (Dab), N- dialkylated ornithine (Orn) and N-dialkylated lysine (Lys), most preferably an amino acid selected from N-dimethylated 2,3-diaminopropionic acid (Dap), N-dimethylated 2,4- diaminobutanoic acid (Dab), N-dimethylated ornithine (Orn) and N-dimethylated lysine (Lys). As will be appreciated, the tertiary amino group can be converted to a quaternary ammonium group -N(R) ₂ \ preferably -N(CH ₃ ) ₂ ⁺ - via conjugation with R ^M1 , L ^D2 or R ^s , preferably R ^s . With respect to their stereochemistry, these amino acid units are preferably D-amino acid units. For the trivalent amino acid unit (i), it is preferred that the amino acid unit is attached in the compound of the invention by three amide bonds. Moreover, it is preferred that the amino acid unit is oriented to provide a -C(O)- coupling group attached to A ^H1 , and a -NH- coupling group attached to R ^CH .

The variable p is 0 or 1, i.e. the hydrophilic modifying group R ^M1 can be present or absent. If it is 0, so that R ^M1 is absent, L ^T1 forms a bond with either L ^D2 (if q is 1 ) or with R ^s (if q is also 0, so that L ^D2 is also absent).

The hydrophilic modifying group R ^M1 is a divalent group which comprises a hydrophilic moiety, i.e. typically a polar or charged moiety. Typically, R ^M1 contains a coupling group at its terminus to which L ^T1 is attached which is suitable to from a binding unit, such as an amide bond (-C(O)- NH-) or an alkylated amide bond (-C(O)-NR-), preferably an amide bond, with a complementary group contained in L ^T1 . Preferably, this coupling group in R ^M1 is a group -C(O)-. At the terminus to which L ^D2 or R ^s is attached, R ^M1 preferably provides a coupling group which is suitable to form a binding unit, such as an amide bond or an alkylated amide bond (-C(O)-NR-), preferably an amide bond, with a complementary group contained in L ^D2 or R ^s . Preferably, this coupling group in R ^M1 is a group -NH-.

Preferably, the hydrophilic modifying group R ^M1 , if present, is a group that can be derived from a hydrophilic amino acid which comprises, in addition to its -NH2 and its -COOH functional group, a further hydrophilic functional group, preferably a hydrophilic functional group selected from -NH ₂ , -COOH, -NH-C(=NH)-

NH ₂ , -C(=0)NH _2I -NH-C(=0)-NH ₂ , -NH-C(=S)-NH ₂ , -0-NH-C(=S)-NH ₂ , -0-NH-C(=N)-NH ₂ -OH and -P(=0)(OH) ₂ , among which a -NH ₂ group is further preferred.

More preferably, the hydrophilic modifying group R ^M1 , if present, is a divalent amino acid unit which is selected from a diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit, most preferably a diaminopropionic acid unit. With a view to their stereochemistry, these amino acid units are preferably D-amino acid units.

It is preferred that the hydrophilic modifying group forms an amide bond with L ^T1 and an amide bond with L ^D2 if q is 1 or with R ^s if q is 0.

The variable q is 0 or 1, i.e. the divalent linking group L ^D2 can be present or absent. If it is 0, so that L ^D2 is absent, R ^s forms a bond with either R ^M1 (if p is 1 ) or with L ^T1 (if p is also 0).

The optional divalent linking group L ^D2 can act as an additional spacer between R ^s and the remainder of the compound of the invention. Typically, L ^D2 contains a coupling group at its terminus to which L ^T1 or R ^M1 is attached which is suitable to from a binding unit, such as an amide bond (-C(O)-NH-) or an alkylated amide bond (-C(O)-NR-), preferably an amide bond, with a complementary group contained in L ^T1 or R ^M1 . Preferably, this coupling group in L ^D2 is a group -C(O)-. At the terminus to which L ^D2 or R ^s is attached, L ^D2 preferably provides a coupling group which is suitable to form a binding unit, such as an amide bond or an alkylated amide bond, preferably an amide bond, with a complementary group contained in L ^D2 or R ^s . Preferably, this coupling group in L ^D2 is a group -NH-.

The divalent linking group L ^D2 , if present, is preferably a group of the formula (L-2):

-[A ^L V- (L-2) wherein

A ^L2 is, independently for each occurrence if w is more than 1 , an amino acid unit; and w is 1 to 5, preferably 1 to 3, more preferably 1 or 2.

Preferably, the amino acid unit(s) A ^L2 is (are) independently selected from a glycine unit and an alanine unit. The alanine unit is preferably a D-alanine unit.

A preferred type of compound of the invention is one of the formula (1.1 ) or a salt thereof: wherein R ^B , L ^D1 , A ^H1 , m, L ^T1 , R ^CH , R ^M1 , L ^D2 and q are as defined herein above, including their preferred embodiments, and R ^S2 is a SiFA group of the formula (S-3), more preferably (S-3a) as defined herein above, i.e.: wherein R ^1S and R ^2S are as defined herein above, including their preferred embodiments.

Among the compounds of formula (1.1 ) or their salts, further preference is given to those of formula (1.2) or their salts: wherein R ^B , L ^D1 , A ^H1 , m, L ^T1 , R ^CH , R ^M1 and R ^S2 are as defined herein above, including their preferred embodiments.

A still more preferred type of compound of the invention is one of the formula (1.3) or a salt thereof: wherein R ^B , L ^D1 , A ^H1 , m, L ^T1 , R ^CH , R ^M1 , p, L ^D2 and q are as defined herein above, including their preferred embodiments, and R ^S3 is a SiFA group of the formula (S-4), more preferably (S-4a) as defined herein above, i.e.:

wherein r, s, R, R ^1S and R ^2S are as defined herein above, including their preferred embodiments.

Among the compounds of formula (1.3) or their salts, further preference is given to those of formula (1.4) and (1.5) or their salts: wherein R ^B , L ^D1 , A ^H1 , m, L ^T1 , R ^CH , R ^M1 , L ^D2 , q and R ^S3 are as defined herein above, including their preferred embodiments.

In line with the above, it will be understood that it is preferred for the compounds of formula (I) and their salts, as well as for the compounds of formula (1.1 ) to (1.5) and their respective salts if

R ^B comprises a group which can be derived from a receptor agonist or receptor antagonist selected from Tyr ³ , Thr ^® -Octreotide (TATE), Tyr ³ -Octreotide (TOC), Thr ^® -Octreotide (ATE); 1- Nal ³ -Octreotide (NOC), 1 -Nal ³ ,Thr ⁸ -octreotide (NOCATE), BzThi ³ -octreotide (BOC), BzThi ³ ,Thr ⁸ - octreotide (BOCATE), JR11 , BASS, and KE121 ; R ^CH comprises a group which can be derived from a chelating agent selected from DOTA, DOTAGA, DOTAM, D03AM, NOTA and NODAGA, and wherein the chelating group optionally comprises a chelated radioactive or non-radioactive cation; and

A ^H1 is selected, independently for each occurrence, from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, citrulline (Cit) unit and a phosphonomethylalanine (Pma) unit.

It is further preferred for the compounds of formula (I) and their salts, as well as for the compounds of formula (1.1 ) to (1.5) and their respective salts, if

R ^B comprises a group which can be derived from a receptor agonist or receptor antagonist selected from Tyr ³ , ThrMDctreotide (TATE), Tyr ³ -Octreotide (TOC), Thr^-Octreotide (ATE); 1- Nal ³ -Octreotide (NOC), 1-Nal ³ ,Thr ⁸ -octreotide (NOCATE), BzThi ³ -octreotide (BOC), BzThP.Thr ⁸ - octreotide (BOCATE), JR11 , BASS, and KE121 ;

R ^CH comprises a group which can be derived from a chelating agent selected from DOTA, DOTAGA, DOTAM, D03AM, NOTA and NODAGA, and wherein the chelating group optionally comprises a chelated radioactive or non-radioactive cation;

A ^H1 is selected, independently for each occurrence, from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, citrulline (Cit) unit and a phosphonomethylalanine (Pma) unit; and R ^M1 if present, is an amino acid unit which is selected from a diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit, and is more preferably a diaminopropionic acid unit.

It is still further preferred for the compounds of formula (I) and their salts, as well as for the compounds of formula (1.1) to (1.5) and their respective salts, if

R ^B comprises a group which can be derived from a receptor agonist or receptor antagonist selected from Tyr ³ , Thi^-Octreotide (TATE), and JR11 ;

R ^CH comprises a group which can be derived from a chelating agent selected from DOTA, DOTAGA, and DOTAM, and wherein the chelating group optionally comprises a chelated radioactive or non-radioactive cation; m is 2 or 3;

A ^H1 is selected, independently for each occurrence, from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, and a citrulline (Cit) unit; and

R ^M1 if present, is an amino acid unit which is selected from a diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit, and is more preferably a diaminopropionic acid unit.

In line with the above discussion of the compounds of formula (I) and their salts, a preferred structure of these compounds is illustrated by formula (la) and their salts: wherein

R ^B and R ^CH are as defined herein above, including preferred embodiments thereof; n1 is 2 to 5, preferably 2 or 3;

R ^L1 is selected, independently for each occurrence from H, a C1-C4 alkyl group, -(CH ₂ )V-NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , and -(CH ₂ ) _v -OH wherein v is 1 to 4; ml is 2 to 5, more preferably 2 or 3;

R ^H1 is selected, independently for each occurrence, from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _V -OH and -(CH ₂ ) _v -P(=0)(0H) ₂ , wherein v is 1 to 4; d is an integer of 0 to 4; e is an integer of 0 to 4; and preferably one of d and e is 0 and the other one is an integer of 1 to 4, more preferably the other one is 1 ; p1 is 0 or 1 ;

R ^H2 is selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _v -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _V -OH and -(CH ₂ ) _v -P(=0)(OH) ₂ wherein v is 1 to 4; q1 is an integer of 0 to 2; R ^L2 is selected from H and CH ₃ , and if p1 is 1 , R ^s1 is selected from a group of formula (S-3) and a group of formula (S-4) wherein r is 1 , 2 or 3, preferably 1 , s is an integer of 1 to 6 and is preferably 1 , R is, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and is more preferably methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound; and if p1 is 0, R ^S1 is a group of formula (S-4) as defined above. It will be understood that the groups of formula (S-3a) and (S-4a) remain even more preferred examples of these.

In formula (la), R ^B and R ^CH are as defined herein, including preferred embodiments thereof, so that (B-1 ) or (B-2) remain preferred structures for R ^B , and (CH-1 ) to (CH-3) or chelates formed with these chelating groups remain strongly preferred structures for R ^CH ,

It will be appreciated that the unit -C(0)-CH(R ^L1 )-NH- within the brackets [,..] _ni represents an amino acid unit, and R ^L1 is H or a side chain of the amino acid unit. If the amino acid unit can be derived from a chiral amino acid, it is preferably in D-configuration. R ^L1 is selected, independently for each occurrence from H, a C1-C4 alkyl group such as methyl, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _v -C(=0)NH ₂ , -(CH ₂ ) _v -NH-C(=0)-NH ₂ , and -(CH ₂ ) _v -OH wherein v is 1 to 4, e.g. 1 or 2. Preferably, each of the amino acid units carrying R ^L1 is independently selected from a glycine unit and an asparagine unit, and still more preferably from a glycine unit and a D-asparagine unit. Most preferred is a glycine unit. Thus, for example, a preferred group -[C(0)-CH(R ^L1 )-NH] _ni - may consist of (i) one Gly unit, (ii) two Gly units, (iii) three Gly units, or (iv) two D-Asn units, and a particularly preferred example is a group -[C(O)- CH(R ^L1 )-NH] _n r consisting of two or three Gly units.

The unit -C(0)-CH(R ^H1 )-NH- within the brackets [...] _mi likewise represents an amino acid unit, and R ^H1 is a side chain of the amino acid unit. The amino acid from which the amino acid unit is derived is preferably in D-configuration. R ^H1 is selected, independently for each occurrence, from

-(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _V -OH and -(CH ₂ ) _v -P(=0)(0H) ₂ , wherein v is 1 to 4.

R ^H1 is preferably selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _v -COOH, -(CH ₂ ) _V -NH-C(=NH)- NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , and -(CH ₂ ) _v -NH-C(=0)-NH ₂ , wherein v is 1 to 4.

Preferably, the amino acid units carrying R ^H1 are independently selected from a 2,3- diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, citrulline (Cit) unit and a phosphonomethylalanine (Pma) unit, more preferably from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, and a citrulline (Cit) unit, and still more preferably from a D-2,3-diaminopropionic acid unit, D-2,4-diaminobutanoic acid unit, D-ornithine unit, D-lysine unit, D-arginine unit, D-glutamic acid unit, D-aspartic acid unit, D-asparagine unit, D-glutamine unit, and a D-citrulline unit. Thus, for example, a preferred group -[C(0)-CH(R ^H1 )-NH] _mi -may consist of (i) two D-Asp units, (ii) two D-Orn units, (iii) two Asn units, or (iv) two D-Asp units and a third unit selected from D- Lys, D-Cit and D-Glu.

The variable d is an integer of 0 to 4, and e is an integer of 0 to 4. It is more preferred that one of d and e is 0, and the other one is 1 to 4, still more preferably the other one is 1. Thus, the most preferred combinations are d is 1 and e is 0, or d is 0 and e is 1.

The trivalent unit the above formula is likewise an amino acid unit. Preferably, it is selected from a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit, more preferably a Dap unit. Still more preferred are a D-2,3-diaminopropionic acid (Dap) unit, D-2,4-diaminobutanoic acid (Dab) unit, D-ornithine (Orn) unit and a D-lysine (Lys) unit, most preferred is a D-Dap unit.

The unit -C(0)-CH(R ^H2 )-NH-, in the above formula within the brackets [...] _Pi , likewise represents an amino acid unit, and R ^H2 is a side chain of the amino acid unit. The amino acid from which the amino acid unit is derived is preferably in D-configuration. R ^H2 is selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _v -OH and -(CH ₂ ) _v -P(=0)(0H) ₂ , wherein v is 1 to 4. Preferably, the amino acid unit carrying R ^H2 is selected from a 2,3-diaminopropionic acid (Dap) unit, 2,4- diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, citrulline (Cit) unit and a phosphonomethylalanine (Pma) unit. Among them, a Dap unit is particularly preferred. More preferably the unit is selected from a D-2,3- diaminopropionic acid unit, D-2,4-diaminobutanoic acid unit, D-ornithine unit, D-lysine unit, D- arginine unit, D-glutamic acid unit, D-aspartic acid unit, D-asparagine unit, D-glutamine unit, D-serine unit, D-citrulline unit and a D-phosphonomethylalanine unit, a most preferred is a D- Dap unit.

The unit -C(0)-CH(R ^L2 )-NH- within the brackets [,..] _qi likewise represents an amino acid unit, and R ^L2 is H or a side chain of the amino acid unit. If R ^L2 is not H, the amino acid from which the amino acid unit is derived is preferably in D-configuration. R ^H2 is selected from H and CH3, and is preferably H.

R ^S1 is selected from a group of formula (S-3) and a group of formula (S-4) as defined herein, and is more preferably a group (S-4):

wherein r is 1 , 2 or 3, preferably 1 , s is an integer of 1 to 6 and is preferably 1 ,

R is, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and is more preferably methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

As noted above, among the groups (S-3), a group (S-3a) is strongly preferred, and among the groups (S-4), the group (S-4a) is strongly preferred.

A preferred type of compound of formula (la) or a salt thereof is one of the formula (la.1 ) or a salt thereof:

(ia.1 ) wherein R ^B , R ^L1 , n1 , R ^H1 , ml , d, e, R ^CH , R ^H2 , R ^L2 and q1 are as defined herein above, including their preferred embodiments, and R ^S2 is a SiFA group of the formula (S-3), more preferably (S- 3a) as defined herein above, i.e.: wherein R ^1S and R ^2S are as defined herein above, including their preferred embodiments. Among the compounds of formula (la.1) or their salts, further preference is given to those of formula (la.2) or their salts: wherein R ^B , R ^L1 , n1 , R ^H1 , ml , d, e, R ^CH , R ^H2 and R ^S2 are as defined herein above, including their preferred embodiments.

A still more preferred type of the compound of formula (la) or a salt thereof is one of the formula (la.3) or a salt thereof: wherein R ^B , R ^L1 , n1, R ^H1 , ml , d, e, R ^CH , R ^H2 , p1 , R ^L2 and q1 are as defined herein above, including their preferred embodiments, and R ^S3 is a SiFA group of the formula (S-4), more preferably (S-4a) as defined herein above, i.e.: wherein r, s, R, R ^1S and R ^2S are as defined herein, including their preferred embodiments.

Among the compounds of formula (la.3) or their salts, further preference is given to those of formula (la.4) and (la.5) or their salts:

wherein R ^B , R ^L1 , n1 , R ^H1 , ml , d, e, R ^CH , R ^H2 , R ^L2 , q1 and R ^S3 are as defined herein above, including their preferred embodiments.

As noted above, the compounds in accordance with the invention encompass the compounds of formula (I) and their salts. Salts are preferably pharmaceutically acceptable salts, i.e. formed with pharmaceutically acceptable anions or cations. Salts may be formed, e.g., by protonation of an atom carrying an electron lone pair which is susceptible to protonation, such as a nitrogen atom, with an inorganic or organic acid, or by separating a proton from an acidic group, such as a carboxylic acid group, e.g. by neutralization with a base. Other charged groups which may be present in the compounds in accordance with the invention and which may provide the compounds in the form of a salt include groups which are continuously charged, such as a quaternary ammonium group comprising an ammonium cation wherein the nitrogen is substituted by four organyl groups, or charged chelate complexes.

As exemplary anions which may be present as counterions in salt forms of the compounds of the invention if the salt form comprises a positively charged form of the compound of formula (I), mention may be made, for example, of an anion selected from chloride, bromide, iodide, sulfate, nitrate, phosphate (such as, e.g., phosphate, hydrogenphosphate, or dihydrogenphosphate salts), carbonate, hydrogencarbonate or perchlorate; acetate, trifluoroacetate, propionate, butyrate, pentanoate, hexanoate, heptanoate, octanoate, cyclopentanepropionate, undecanoate, lactate, ma!eate, oxalate, fumarate, tartrate, malate, citrate, nicotinate, benzoate, salicylate or ascorbate; sulfonates such as methanesulfonate, ethanesulfonate, 2-hydroxyethanesulfonate, benzenesulfonate, p-toluenesulfonate (tosylate), 2-naphthalenesulfonate, 3-phenylsulfonate, or camphorsulfonate. Since trifluoroacetic acid is frequently used during the synthesis of peptides, trifluoroacetate salts are typical salts which are provided if a compound comprising a peptide structure is formed. Such trifluoroacetate salts may be converted e.g. to acetate salts during their workup.

As exemplary cations which may be present as counterions in salt forms of the compounds of the invention if the salt form comprises a negatively charged form of the compound of formula (I), mention may be made, for example, of a cation selected from alkali metal cations, such as lithium, sodium or potassium, alkaline earth metal cations, such as calcium or magnesium; and ammonium (including ammonium ions substituted by organic groups).

The compound in accordance with the invention is preferably capable of binding to an SST receptor, preferably to SST2, with an affinity reflected by an IC50 value of 50 nM or less, more preferably 10 nM or less, still more preferably 5 nM or less.

The compound in accordance with the invention preferably exhibits an octanol-water distribution coefficient (also referred to as IogD7.4 or logP value), of - 1.0 or less, more preferably - 2.0 or less. It is generally not below - 4.0.

This distribution coefficient may be determined by measuring the equilibrium distribution, e.g. at room temperature (20°C) of a compound in accordance with the invention in a two-phase system containing equal amounts, such as 1.00 ml each, of n-octanol and PBS (pH = 7.4), and calculating the logD7.4 value as logio(concentration in octanol/concentration in PBS). Instead of the (absolute) concentration of the compound in accordance with the invention in the octanol and the PBS, a parameter which is proportional to the concentration of the compound in each phase may also be used for the calculation, such as the activity of radiation if the compound comprises a radioactive moiety, e.g. a radioactive chelate.

The compounds of the invention can provide advantageous binding characteristics to human serum albumin (HSA). Moderate to low HSA binding values, expressed as the apparent molecular weight in kDa and determined via radio inversed affinity chromatography (RIAC) as described in the examples section below can be achieved. Preferably, the HSA binding value is less than 22 kDa, more preferably below 10 kDa.

As exemplary compounds in accordance with the invention, the following are further mentioned.

Compound 23 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 19 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 39 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 40 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 20 having the formula shown in the Examples section below, a compound wherein the DOTAGA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 41 having the formula shown in the Examples section below, a compound wherein the DOTAGA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 42 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 42 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 36 having the formula shown in the Examples section below, a compound wherein the D03AM chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 37 having the formula shown in the Examples section below, a compound wherein the DOTAGA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 24 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 38 having the formula shown in the Examples section below, a compound wherein the D03AM chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 48 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 49 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 50 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 54 having the formula shown in the Examples section below, a compound wherein the DOT AM (or D03AM) chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 55 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 56 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 57 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 58 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 59 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 61 having the formula shown in the Examples section below, a compound wherein the DOTAM (or D03AM) chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 44 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 45 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 46 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 47 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 51 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 60 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 52 having the formula shown in the Examples section below, a compound wherein the DOT A chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

Compound 53 having the formula shown in the Examples section below, a compound wherein the DOTA chelating group shown in the formula forms a chelate with a chelated radioactive or non-radioactive cation, or any salt thereof.

To the extent that these exemplary compounds or salts comprise a chelated radioactive or non-radioactive cation, the cation is preferably a cation of Ga, Lu, or Pb.

In a further aspect, the present invention provides a pharmaceutical composition (also referred to as a therapeutic composition) comprising or consisting of one or more types, preferably one type, of the ligand compound in accordance with the invention, i.e. a compound of formula (I) including any preferred embodiments thereof as discussed herein or a salt thereof. In a related aspect, the ligand compound in accordance with the invention is provided for use in therapy or for use as a medicament. Thus, the ligand compound of the invention can be used in a therapeutic method, which method may comprise administering the ligand compound to a subject. The subject may be a human or an animal and is preferably a human.

The therapy or therapeutic method referred to above aims at the treatment or prevention of a disease or disorder of the human or animal body, generally a disease or disorder that is associated with increased or aberrant expression of a somatostatin receptor, preferably a disease or disorder associated with increased or aberrant expression of SST2. The disease or disorder to be treated or prevented can be cancer, preferably a neuroendocrine tumor.

For example, a compound in accordance with the invention comprising a chelated radioactive cation, such as a ¹⁷⁷ Lu cation or a ⁶⁸ Ga cation, can be advantageously used in radiotherapy, such as the radiotherapy of a disease or disorder as discussed above.

In another aspect, the present invention provides a diagnostic composition comprising or consisting of one or more types, preferably one type, of the ligand compound in accordance with the invention, i.e. a compound of formula (I) including any preferred embodiments thereof as discussed herein or a salt thereof. In a related aspect, the ligand compound in accordance with the invention is provided for use in a method of diagnosis in vivo of a disease or disorder. Thus, the ligand compound in accordance with the invention can be used in a method of diagnosis, which method may comprise administering the ligand compound to a subject and detecting the ligand compound in the subject, or monitoring the distribution of the ligand compound in the subject thereby detecting or monitoring the disease to be diagnosed. For example, nuclear imaging by means of Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT), respectively, can be used for detecting or monitoring a ligand compound in accordance with the invention. The subject may be a human or an animal and is preferably human. Alternatively, a method of diagnosis may also comprise adding the ligand compound to a sample, e.g. a physiological sample obtained from a subject in vitro or ex vivo, and detecting the ligand compound in the sample.

The method of diagnosis referred to above aims at the identification of a disease or disorder of the human or animal body, generally a disease or disorder that is associated with increased or aberrant expression of a somatostatin receptor, preferably a disease or disorder associated with increased or aberrant expression of SST ₂ . Thus, in terms of a diagnostic application, the compounds of the invention are preferably provided for use in a method of diagnosis in vivo of cancer, more preferably a neuroendocrine tumor.

For example, a compound of the invention wherein the SiFA group comprises a ¹⁸ F fluoride, or a compound of the invention wherein the chelating groups comprises a chelated radioactive cation, e.g. a ⁶⁸ Ga cation, can be advantageously used for nuclear diagnostic imaging, such as diagnosis via positron emission tomography (PET) or via Single Photon Emission Computed Tomography (SPECT).

It will be understood that suitability for a therapeutic and a diagnostic application is not mutually exclusive, i.e. a compound in accordance with the invention may be suitable for both applications. For example, a compound comprising a chelated ¹⁷⁷ Lu cation can be used both for therapeutic and diagnostic imaging applications. Moreover, due to the presence of a chelating group and a SiFA group, the compounds of the invention are suitable as radiohybrid (rh) ligands. Such a rh ligand can be alternatively labeled with [ ¹⁸ F] fluoride (e.g. for PET) or a radiometal (such as a ⁶⁸ Ga cation for PET, or a ¹⁷⁷ Lu cation for radiotherapy). When a rh ligand is labeled with [ ¹⁸ F]fluoride, a cold (non-radioactive) metal cation can, but not necessessarily must be complexed elsewhere in the molecule, and when it is labeled with a corresponding radioactive metal cation, cold [ ¹⁹ F] fluorine can be included. Therefore, the ¹⁸ F-labeled peptide and the corresponding radiometal-labeled analog can possess the same chemical structure and thus identical in vitro and in vivo properties, thereby allowing the generation of structurally identical theranostic tracers with exactly the same in vivo properties of the diagnostic and therapeutic tracers (e.g. ¹⁸ F/ ¹⁷⁷ Lu analogs) [24],

Thus, in line with this approach the ligand compounds of the invention include compounds wherein the silicon-fluoride acceptor group is labeled with ¹⁸ F and the chelating group contains a chelated non-radioactive cation (such as ^nat Lu or ^nat Ga), and compounds wherein the chelating group contains a chelated radioactive cation (such as ¹⁷⁷ Lu or ⁶⁸ Ga) and the silicon- fluoride acceptor group is not labeled with ¹⁸ F (thus carrying a ¹⁹ F). Likewise, the invention provides the compounds of the invention for use in a hybrid method of diagnosis in vivo and therapy of a disease or disorder associated with increased or aberrant expression of a somatostatin receptor as discussed above, wherein the method involves first the administration of a compound of the invention wherein the silicon-fluoride acceptor group is labeled with ¹⁸ F and the chelating group contains a chelated non-radioactive cation (such as ^nat Lu or ^nat Ga), and subsequently of a compound wherein the chelating group contains a chelated radioactive cation and the silicon-fluoride acceptor group is not labeled with ¹⁸ F.

Thus, in another aspect, the present invention provides a dedicated composition comprising or consisting of one or more types, preferably one type, of the ligand compound in accordance with the invention, i.e. a compound of formula (I) including any preferred embodiments thereof as discussed herein, or a salt thereof. In a related aspect, the ligand compound in accordance with the invention is provided for use in a method of in vivo imaging of a disease or disorder. Thus, the ligand compound in accordance with the invention can be used in an imaging method, which method may comprise administering the ligand compound to a subject and detecting the ligand compound in the subject and monitoring the distribution of the ligand compound in vivo at different time points after injection with the aim to calculate the dosimetry prior or during a therapeutic treatment. The subject may be a human or an animal and is preferably human.

The imaging method referred to above aims at the calculation of the dosimetry prior or during a therapeutic treatment of a disease or disorder of the human or animal body, generally a disease or disorder that is associated with increased or aberrant expression of a somatostatin receptor, preferably a disease or disorder associated with increased or aberrant expression of SST2. Thus, in terms of such application, the compounds of the invention are preferably provided for use in an in vivo imaging method for cancer, more preferably a neuroendocrine tumor. For example, a compound of the invention wherein the SiFA group comprises a ¹⁸ F fluoride and non-radioactive ^nat Lu, or a compound of the invention wherein the chelating group comprises a chelated radioactive cation, e.g. a ¹⁷⁷ Lu cation, whereas the SiFA is nonradioactive, can be advantageously used for nuclear imaging by means of Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT), respectively, to monitor the distribution of the applied compound and thereafter calculate the individual dosimetry by means of the quantitative distribution kinetics.

The pharmaceutical or diagnostic composition may further comprise one or more pharmaceutically acceptable carriers, excipients and/or diluents. Examples of suitable pharmaceutical carriers, excipients and/or diluents are well known in the art and include phosphate buffered saline solutions, amino acid buffered solutions (with or without saline), water for injection, emulsions, such as oil/water emulsions, various types of wetting agents, sterile solutions etc. Compositions comprising such carriers can be formulated by well-known conventional methods. These compositions can be administered to the subject at a suitable dose. Administration of the suitable compositions may be accomplished in different ways, e.g., by intravenous, intraperitoneal, subcutaneous, intramuscular, topical, intradermal, intranasal or intrabronchial administration. It is particularly preferred that said administration is carried out by intravenous injection and/or delivery. The compositions may be administered directly to the target site. The dosage regimen will be determined by the attending physician and clinical factors. As is well known in the medical arts, dosages for any one patient depends upon many factors, including the patient's size, body surface area, age, the particular compound to be administered, dosimetry, sex, time and route of administration, general health, and other drugs being administered concurrently. The compounds may be administered e.g. in amounts between 0,1 ng and 10 pg/kg body weight. For example, in diagnostic applications, a typical dosage amount of the compounds of the invention or their salts is < 100 pg/patient, e.g. in the range of 0.1 to 30 pg/patient, however, if appropriate, higher or lower dosages can be envisaged. A typical dosage amount of the compounds of the invention or their salts in a radiotherapeutic application is in the range of 50 to 200 pg/patient, preferably 75 to 150 pg/patient, however, if appropriate, higher or lower dosages can be envisaged.

The following items summarize aspects of the invention. It will be understood that these items are closely related to the above parts of the description, and that the information provided in these items may supplement the above parts of the description and vice versa. 1. A compound of formula (I) or a salt thereof: wherein:

R ^B is a binding motif which is able to bind to a somatostatin receptor;

L ^D1 is a divalent linking group; m is an integer of 2 to 6, preferably 2 to 5, more preferably 2 or 3;

A ^H1 is, independently for each occurrence, an amino acid unit derived from a hydrophilic amino acid which comprises, in addition to its -IMH2 and its -COOH functional group, a further hydrophilic functional group, and wherein one of the m units A ^H1 may further carry a hydrophilic unit other than an amino acid bound to its hydrophilic functional group;

L ^T1 is a trivalent linking group; R ^CH is a chelating group which optionally contains a chelated radioactive or non-radioactive cation;

R ^M1 is a hydrophilic modifying group, and p is 0 or 1 ;

L ^D2 is a divalent linking group, and q is 0 or 1 ; and

R ^s is a silicon-fluoride acceptor (SiFA) group of one of the following formulae, which comprises a silicon atom and a fluorine atom, and which can be labeled with ¹⁸ F by isotopic exchange of ¹⁹ F by ¹⁸ F or which is labeled with ¹⁸ F: if p is 1 , R ^s is a group of formula (S-3) or a group of formula (S-4): wherein r is 1, 2 or 3, preferably 1, s in -(CEhV is an integer of 1 to 6 and is preferably 1, the groups R are, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and are more preferably both methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound; and if p is 0, R ^s is a group of formula (S-4) as defined above. 2. The compound or salt of item 1 , wherein the binding motif is able to bind to the somatostatin receptor 2.

3. The compound or salt of item 1 or 2, wherein the binding motif R ^B is a group which can be derived from a receptor agonist or receptor antagonist selected from Tyr^Thi^-Octreotide (TATE), Tyr ³ -Octreotide (TOC), Thi^-Octreotide (ATE); 1-Nal ³ -Octreotide (NOC), 1-Nal ³ ,Thr ⁸ - octreotide (NOCATE), BzThi ³ -octreotide (BOC), BzThi ³ ,Thr ^® -octreotide (BOCATE), JR11 , BASS, and KE121.

4. The compound or salt of item 1 or 2, wherein the binding motif R ^B is a group of the formula (B-1) or (B-2):

wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

5. The compound or salt of any of items 1 to 4, wherein the chelating group R ^CH comprises at least one of

(i) a macrocyclic ring structure with 8 to 20 ring atoms of which 2 or more, preferably 3 or more, are selected from oxygen atoms and nitrogen atoms; and

(ii) an acyclic, open chain chelating structure with 8 to 20 main chain atoms of which 2 or more, preferably 3 or more are heteroatoms selected from oxygen atoms and nitrogen atoms.

6. The compound or salt in accordance with any of items 1 to 5, wherein the chelating group R ^CH is a group which can be derived from a chelating agent selected from diethylenetriaminepentamethylenephosphonic acid (EDTMP) and its derivatives, diethylenetriaminepentaacetic acid (DTPA) and its derivatives, bis(carboxymethyl)- 1 ,4,8, 11 -tetraaza-bicyclo[6.6.2] hexadecane (CBTE2a), cyclohexyl-1 ,2-diaminetetraacetic acid (CDTA), 4-(1 ,4,8,11-tetraazacyclotetradec-1-yl)-methylbenzoic acid (CPTA), N'-[5- [acetyl(hydroxy)amino]-'pentyl]-N-[5-[[4-[5-aminopentyl-(hyd roxy)amino]-4-oxobutanoyl]- amino]pentyl]-N-hydroxybutandiamide (DFO) and derivatives thereof, 1 ,4,7,10- tetraazacyclododecane-1 ,7-diacetic acid (D02A), 1 ,4,7,10-tetraazacyclododecan-N,N',N",N"'- tetraacetic acid (DOTA), 2-[1 ,4,7,10-tetraazacyclododecane-4,7,10-triacetic acid]- pentanedioic acid (DOTAGA or DOTA-GA), 1 ,4,7,10-tetrakis(carbamoylmethyl)-1 ,4,7,10- tetraazacyclododecane (DOTAM), N,N'-dipyridoxylethylendiamine-N,N'-diacetate-5,5'- bis(phosphat) (DPDP), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine-N,N'- tetraacetic acid (EDTA), ethyleneglykol-0,0-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), N,N-bis(hydroxybenzyl)-ethylenediamine-N,N'-diacetic acid (HBED), hydroxyethyidiaminetriacetic acid (HEDTA), 1-(p-nitrobenzyl)-1 ,4,7,10-tetraazacyclodecan-

4.7.10-triacetate (HP-DOA3), 6-hydrazinyl-N-methylpyridine-3-carboxamide (HYNIC), 1 ,4,7- triazacyclononan-1 -succinic acid-4, 7-diacetic acid (NODASA), 1-(1-carboxy-3-carboxypropyl)-

4.7-(carboxy)-1,4,7-triazacyclononane (NODAGA), 1,4,7-triazacyclononanetriacetic acid (NOTA), 4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2]hexad ecane (TE2A), 1,4,8,11-tetraazacyclododecane-1 ,4,8,11-tetraacetic acid (TETA), terpyridine- bis(methyleneamine) tetraacetic acid (TMT), 1 ,4,7,10-tetraazacyclotridecan-N,N',N",N'"- tetraacetic acid (TRITA), and triethylenetetraaminehexaacetic acid (TTHA), N,N'-bis[(6- carboxy-2-pyridil)methyl]-4,13-diaza-18-crown-6 (H ₂ macropa), 4-a m i n o-4-{2- [( 3- hyd roxy- 1 ,6- dimethyl-4-oxo-1,4-dihydro-pyridin-2-ylmethyl)-carbamoyl]-et hyl} heptanedioic acid bis-[(3- h yd roxy- 1 ,6-dimethyl-4-oxo-1 ,4-dihydro-pyridin-2-ylmethyl)-amide] (THP), 1 ,4,7- triazacyclononane-1 ,4,7-tris[methylene(2-carboxyethyl)phosphinic acid (TRAP), 2-(4,7,10- tris(2-amino-2-oxoethyl)-1 ,4,7,10-tetraazacyclododecan-1-yl)acetic acid (D03AM), and

1.4.7.10-tetraazacyclododecane-1 ,4,7, 10-tetrakis[methylene(2-carboxyethylphosphinic acid)] (DOTPI), S-2-(4-isothiocyanatobenzyl)-1 ,4,7,10-tetraazacyclododecane tetraacetic acid, hydrazinonicotinic acid (HYNIC), 6-amino-6-methylperhydro-1,4-diazepine-N,N,N',N'- tetraacetic acid (AAZTA) and derivatives thereof, such as (6-pentanoic acid)-6-(amino)methyl- 1 ,4-diazepine triacetate (DATA), pentadeca-1 ,4,7,10,13-penta-aminopentaacetic acid (PEPA), hexadeca-1 ,4,7,10,13,16-hexaamine-hexaacetic acid (HEHR), 4-{[bis(phosphonomethyl)) carbamoyl] methyl}-7,10-bis(carboxymethyl)-1 ,4,7,10-tetraazacyclododec-1-yl) acetic acid (BPAMD), N-(4-{[bis (phosphonomethyl)) carbamoyl] methyl}-7,10-bis (carboxymethyl)-nona-

1.4.7-triamine triacetic acid (BPAM), 1 ,2-[{6- (carboxylate) pyridin-2-yl} methylamine] ethane (DEDPA, H2DEDPA), deferoxamine (DFO) and its derivatives, deferiprone, (4-acetylamino-4- yl) (2-[(3-hydroxy-1 ,6-dimethyl-4-oxo-1 ,4-dihydro-pyridin-2-ylmethyl)-carbamoyl]-ethyl}- heptanedioic acid bis-[(3-hydroxy-1 ,6 -dimethyl-4-oxo-1 ,4-dihydro-pyridin-2-ylmethyl)-amide] (CP256) and its derivatives such as YM103; tetraazycyclodecane-phosphinic acid (TEAP), 6- amino-6-methylperhydro-1 ,4-diazepine-N,N,N',N'-tetraacetic acid (AAZTA); 1-N-(4- aminobenzyl) -3,6,10,13,16,19-hexaazabicyclo [6.6.6]-eicosane-1 ,8-diamine (SarAr), 6,6'-[{9- hydroxy-1, 5-bis-(methoxycarbonyl)-2,4-di(pyridin-2-yl)-3,7-diazabicycl o[3.3.1]nonane-3,7- diyl}bis(methylene)]dipicolinic acid (H ₂ bispa ² ), 1 ,2-[{6-(carboxylato)pyridin-2-yl}methylamino]- ethane (H ₂ dedpa), N,N'-bis(6-carboxy-2-pyndylmethyl)-ethylenediamine-N,N'-diac etic acid (hhoctapa), N,N'-bis(2-hydroxy-5-sulfonylbenzyl)-N,N'-bis-(2-methylpyrid yl)ethylenediamine (HeSbbpen) and derivatives thereof, triethylenetetramine-N , N , N’, N", N"', N'"-hexaacetic (TTHA), 2-aminomethylpiperidine triacetic acid (2-AMPTA) and derivatives thereof, such as 2- (N-(2-Hydroxybenzyl)aminomethyl)piperidine (2-AMPTA-HB) further functionalized derivative of 2-AMPTA with additional functional groups suitable for conjugation to peptidic structures, 4- nitro-2-hydroxybenzyl-2-{[(6)-trans-2-[benzyl(carboxymethyl) amino]cyclohexyl] (carboxymethyl)amino}acetic acid (RESCA) and derivatives thereof, and 6-carboxy-1 ,4,8,11- tetraazaundecane (N ₄ ) and derivatives thereof, and wherein the chelating group optionally comprises a chelated radioative or non-radioactive cation.

7. The compound or salt of item 6, wherein the chelating group R ^CH is a group which can be derived from a chelating agent selected from CBTE2a, DOTA, DOTAGA, DOTAM, NODASA, NODAGA, NOTA, TE2A, D03AM, SarAr, 2-AMPTA, 2-AMPTA-HB and RESCA, and wherein the chelating group optionally comprises a chelated radioative or non-radioactive cation.

8. The compound or salt of item 7, wherein the chelating group R ^CH is a group which can be derived from a chelating agent selected from DOTA, DOTAGA, DOTAM, D03AM, NOTA and NODAGA, and wherein the chelating group optionally comprises a chelated radioative or non-radioactive cation.

9. The compound or salt of any of items 1 to 8, wherein R ^CH is a group of the formula (CH- 1 ), (CH-2) or (CH-3) which optionally contains a chelated radioactive or non-radioactive cation:

(CH-1) wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

10. The compound or salt of any of items 1 to 9, wherein the chelated cation, if present, comprises or consists of a cation selected from cations of ⁴³ Sc, ⁴⁴ Sc, ⁴⁷ Sc, ⁵¹ Cr, ^52m Mn, ⁵⁵ Co, ⁵⁷ Co, ⁵⁸ Co, ⁵² Fe, ⁵⁶ Ni, ⁵⁷ Ni, ⁶² Cu, ⁶⁴ Cu, ⁶⁷ Cu, ⁶⁶ Ga, ⁶⁸ Ga, ⁶⁷ Ga, ⁸⁹ Zr, ⁹⁰ Y, ⁸⁶ Y, ^94m Tc, ^99m Tc, ⁹⁷ Ru, ⁱ ° ⁵ Rh, ^I09 p _di u ⁱ Ag, ^110m ln, ¹¹¹ ln, ^113m ln, ^114m ln, ^117m Sn, ¹²¹ Sn, ¹²⁷ Te, ¹⁴² Pr, ¹⁴³ Pr, ¹⁴⁷ Nd, ¹⁴⁹ Gd, ¹⁴⁹ Pm, ¹⁵¹ Pm, ¹⁴⁹ Tb, ¹⁵² Tb, ¹⁵⁵ Tb, ¹⁵³ Sm, ¹⁵⁶ Eu, ¹⁵⁷ Gd, ¹⁵⁵ Tb, ¹⁶¹ Tb, ¹⁶⁴ Tb, ¹⁶¹ Ho, ¹⁶⁶ Ho, ¹⁵⁷ Dy, ¹⁶⁵ Dy, ¹⁶⁶ Dy, ¹⁶⁰ Er, ¹⁶⁵ Er, ¹⁶⁹ Er, ¹⁷¹ Er, ¹⁶⁶ Yb, ¹⁶⁹ Yb, ¹⁷⁵ Yb, ¹⁶⁷ Tm, ¹⁷² Tm, ¹⁷⁷ Lu, ¹⁸⁶ Re, ¹⁸⁶⁹ Re, ¹⁸⁸ Re, ¹⁸⁸ W, ¹⁹¹ Pt, ^195m Pt, ¹⁹⁴ lr, ¹⁹⁷ Hg, ¹⁹⁸ Au, ¹⁹⁹ Au, ²¹² Pb, ²⁰³ Pb, ²¹¹ At, ²¹² Bi, ²¹³ Bi, ²²³ Ra, ²²⁴ Ra, ²²⁵ Ac, ²²⁶ Th and ²²⁷ Th, and from nonradioactive isotopes of any of these metals, or is a cationic molecule comprising ¹⁸ F or ¹⁹ F, such as ¹⁸ F-[AIF] ²⁺ .

11. The compound or salt of any of items 1 to 10, wherein the divalent linking group L ^D1 comprises a divalent oligo- or polyethylene glycol group; preferably a divalent oligo- or polyethylene glycol group having 10 or less ethylene glycol units, and more preferably a divalent oligo- or polyethylene glycol group having 2 to 5 ethylene glycol units.

12. The compound or salt of item 11 , wherein L ^D1 is a divalent group of formula (L-1 a):

-C(0HCH ₂ ) _a -(0-CH ₂ -CH ₂ ) _b -NH- (L-1 a) wherein a is 1 or 2, preferably 1 ; b is an integer of 2 to 5, preferably 2 or 3.

13. The compound or salt of any of items 1 to 10, wherein the divalent linking group L ^D1 comprises a divalent amino acid unit or a divalent chain of amino acid units, more preferably a divalent chain of 2 to 5 amino acid units, still more preferably a divalent chain of 2 or 3 amino acid units

14. The compound or salt of item 13, wherein L ^D1 is is represented by formula (L-1 b):

-[A ^L V (L-1b) wherein

A ^L1 is, independently for each occurrence if n is more than 1 , an amino acid unit; and n is an integer of 1 to 5, preferably 2 to 5, more preferably 2 or 3.

15. The compound or salt of item 13 or 14, wherein the amino acid units in L ^D1 do not contain any free amino groups, free acid groups, or salts thereof.

16. The compound or salt of any of items 13 to 15, wherein each amino acid unit in L ^D1 is selected, independently for each occurrence if more than one amino acid unit is present in L ^D1 , from a glycine (Gly) unit, alanine (Ala) unit, b-alanine unit, asparagine (Asn) unit, glutamine (Gin) unit, and citrulline (Cit) unit.

17. The compound or salt of any of items 1 to 16, wherein the further hydrophilic functional group of the amino acid units A ^H1 are selected, independently for each occurrence, from - NH _2I -COOH, -NH-C(=NH)-NH _2I -C(=0)NH ₂ , -NH-C(=0)-NH ₂ , -OH and -P(=0)(OH) ₂ .

18. The compound or salt of any of items 1 to 17, wherein each of the m amino acid units A ^H1 comprises, independently for each occurrence, a side chain having a terminal hydrophilic functional group, which side chain is selected from

-(CH ₂ ) _v -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _V -OH and -(CH ₂ ) _v -P(=0)(0H) ₂ wherein v is 1 to 4, and wherein the terminal functional group of the above side chain in one of the m units A ^H1 may form a bond with an additional hydrophilic unit other than an amino acid unit.

19. The compound or salt of item 18, wherein each of the m amino acid units A ^H1 comprises, independently for each occurrence, a side chain having a terminal hydrophilic functional group, which side chain is selected from

-(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , and -(CH ₂ ) _V -NH-C(=0)-NH ₂ , wherein v is 1 to 4, and wherein the terminal functional group of the above side chain in one of the m units A ^H1 may form a bond with an additional hydrophilic unit other than an amino acid unit.

20. The compound or salt of any of items 1 to 18, wherein the amino acid units A ^H1 are selected, independently for each occurrence, from a 2,3-diaminopropionic acid (Dap) unit, 2,4- diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, serine (Ser) unit, citrulline (Cit) unit and a phosphonomethylalanine (Pma) unit.

21. The compound or salt of item 20, wherein the amino acid units A ^H1 are selected, independently for each occurrence, from a 2,3-diaminopropionic acid (Dap) unit, 2,4- diaminobutanoic acid (Dab) unit, ornithine (Orn) unit, lysine (Lys) unit, arginine (Arg) unit, glutamic acid (Glu) unit, aspartic acid (Asp) unit, asparagine (Asn) unit, glutamine (Gin) unit, and a citrulline (Cit) unit.

22. The compound or salt of any of items 1 to 21 , wherein the hydrophilic unit other than the amino acid unit which is optionally bound to A ^H1 is a carbohydrate group or a trimesic acid group.

23. The compound or salt of any of items 1 to 22, wherein L ^T1 is a trivalent amino acid unit selected from

(i) a 2,3-diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit; or

(ii) a trivalent amino acid unit comprising a -N(R) ₂ ⁺ - group, wherein the groups R are independently C1 to C6 alkyl, and are preferably methyl, and which unit can be derived from a trifunctional amino acid comprising a tertiary amino group selected from N-dialkylated 2,3- diaminopropionic acid (Dap), N-dialkylated 2,4-diaminobutanoic acid (Dab), N-dialkylated ornithine (Orn) and N-dialkylated lysine (Lys). 24. The compound or salt of any of items 1 to 23, wherein p is 1 and the hydrophilic modifying group R ^M1 is a group that can be derived from a hydrophilic amino acid which comprises, in addition to its -NH2 and its -COOH functional group, a further hydrophilic functional group, preferably a hydrophilic functional group selected from -NH2, -COOH, -NH- C(=NH)-NH ₂ , -C(=0)NH ₂ , -NH-C(=0)-NH ₂ , -OH and -P(=0)(0H) ₂ , or wherein p is 0.

25. The compound or salt of any of items 1 to 23, wherein p is 1 and the hydrophilic modifying group R ^M1 is an amino acid unit which is selected from a diaminopropionic acid (Dap) unit, 2,4-diaminobutanoic acid (Dab) unit, ornithine (Orn) unit and a lysine (Lys) unit, more preferably a diaminopropionic acid unit, or wherein p is 0.

26. The compound or salt of any of items 1 to 25, wherein q is 1 and the divalent linking group L ^D2 is a group of the formula (L-2), or q is 0;

-[A ^L2 ]w~ (L-2) wherein

A ^L2 is, independently for each occurrence if w is more than 1 , an amino acid unit; and w is 1 to 5, preferably 1 to 3, more preferably 1 or 2.

27. The compound or salt of item 26, wherein q is 1 and the amino acid unit(s) A ^L2 is (are) independently selected from a glycine unit and an alanine unit, or q is 0.

28. The compound or salt of any of items 1 to 27, which is a compound of formula (1.2) or a salt thereof: wherein

R ^B , L ^D1 , A ^H1 , m, L ^T1 , R ^CH , and R ^M1 are defined as in the preceding items; and R ^S2 is a group of the formula (S-3):

(S-3) wherein

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

29. The compound or salt of any of items 1 to 27, which is a compound of formula (1.4) or (1.5) or a salt of these: wherein

R ^B , L ^D1 , A ^H1 , m, L ^T1 , R ^M1 , L ^D2 , q and R ^CH are defined as in the preceding items; and R ^S3 is a group of the formula (S-4):

(S-4) wherein r is 1 , 2 or 3, preferably 1 , s is an integer of 1 to 6 and is preferably 1 ,

R is, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and is more preferably methyl,

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

30. The compound or salt of any of items 1 to 27, which is a compound of formula (la) or a salt thereof: wherein

R ^B , and R ^CH are defined as in the preceding items; n1 is 2 to 5, preferably 2 or 3;

R ^L1 is selected, independently for each occurrence from H, a C1-C4 alkyl group, -(CH ₂ )V-NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , and -(CH ₂ ) _v -OH wherein v is 1 to 4; ml is 2 to 5, more preferably 2 or 3;

R ^H1 is selected, independently for each occurrence, from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _v -OH and -(CH ₂ ) _V -P(=0)(OH) ₂ , wherein v is 1 to 4; d is an integer of 0 to 4, preferably 0 or 1 ; e is an integer of 0 to 4, preferably 0 or 1 ; and more preferably one of d and e is 1 , and the other one is 0; p1 is 0 or 1 ;

R ^H2 is selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _v -OH and -(CH ₂ ) _V -P(=0)(0H) ₂ wherein v is 1 to 4; q1 is an integer of 0 to 2;

R ^L2 is selected from H and CH3, and if p1 is 1 , R ^s1 is selected from a group of formula (S-3) and a group of formula (S-4)

(S-4) wherein r is 1 , 2 or 3, preferably 1 , s is an integer of 1 to 6 and is preferably 1 , R is, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and is more preferably methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line marks a bond which attaches the group to the remainder of the compound; and if p1 is 0, R ^S1 is a group of formula (S-4) as defined above.

31. The compound or salt of item 30, which is a compound of formula (la.2) or a salt thereof; wherein

R ^B and R ^CH are defined as in the preceding items; n1 is 2 to 5, preferably 2 or 3;

R ^L1 is selected, independently for each occurrence from H, a C1-C4 alkyl group, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , and -(CH ₂ ) _v -OH wherein v is 1 to 4; ml is 2 to 5, more preferably 2 or 3;

R ^H1 is selected, independently for each occurrence, from

-(CH ₂ )v-NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)- NH ₂ , -(CH ₂ ) _V -OH and -(CH ₂ ) _V -P(=0)(0H) ₂ wherein v is 1 to 4; d is an integer of 0 to 4; e is an integer of 0 to 4; and preferably one of d and e is 0 and the other one is an integer of 1 to 4, more preferably the other one is 1 ;

R ^H2 is selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _v -COOH, -(CH ₂ ) _V -NH-C(=NH)- wherein

(S-3) wherein

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl, and wherein the dashed line marks a bond which attaches the group to the remainder of the compound.

32. The compound or salt of item 30, which is a compound of formula (la.4) or a salt thereof or a compound of formula (la.5) or a salt thereof:

(la, 5) wherein

R ^B and R ^CH are defined as in the preceding items; n1 is 2 to 5, preferably 2 or 3;

R ^L1 is selected, independently for each occurrence from H, a C1-C4 alkyl group, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , and -(CH ₂ ) _y -OH wherein v is 1 to 4; ml is 2 to 5, more preferably 2 or 3; R ^H1 is selected, independently for each occurrence, from -(CH ₂ ) _V -

NH ₂ , -(CH ₂ ) _V -COOH, -(CH ₂ ) _V -NH-C(=NH)-

NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _v -OH and -(CH ₂ ) _v -P(=0)(0H) ₂ wherein v is 1 to 4; d is an integer of 0 to 4; e is an integer of 0 to 4; and preferably one of d and e is 0 and the other one is an integer of 1 to 4, more preferably the other one is 1;

R ^H2 is selected from -(CH ₂ ) _V -NH ₂ , -(CH ₂ ) _v -COOH, -(CH ₂ ) _V -NH-C(=NH)-NH ₂ , -(CH ₂ ) _v -C(=0)NH ₂ , -(CH ₂ ) _V -NH-C(=0)-NH ₂ , -(CH ₂ ) _v -OH and -(CH ₂ ) _v -P(=0)(0H) ₂ wherein v is 1 to 4; q1 is 0 an integer of 0 to 2;

R ^L2 is selected from H and Chb, and R ^S3 is a group of the formula (S-4): wherein r is 1 , 2 or 3, preferably 1 , s is an integer of 1 to 6 and is preferably 1 ,

R is, independently, H or C1 to C6 alkyl, preferably H or C1 to C2 alkyl, and is more preferably methyl, and

R ^1S and R ^2S are independently from each other a linear or branched C3 to C10 alkyl group, preferably R ^1S and R ^2S are selected from isopropyl and tert-butyl, and more preferably R ^1S and R ^2S are tert-butyl; and wherein the dashed line attaches the group to the remainder of the compound.

33. The compound or salt of any of items 30 to 33, wherein R ^H1 is selected, independently for each occurrence, from -(CH ₂ ) _v -NH ₂ , -(CH ₂ ) _v -COOH, -(CH ₂ ) _V -NH-C(=NH)- NH ₂ , -(CH ₂ ) _V -C(=0)NH ₂ , and -(CH ₂ ) _v -NH-C(=0)-NH ₂ , wherein v is 1 to 4.

34. The compound or salt of any of items 1 to 33, wherein the chelating group contains a chelated radioactive cation and the silicon-fluoride acceptor group is not labeled with ¹⁸ F.

35. The compound or salt of item 34, wherein the chelated radioactive cation is a cation of ¹⁷⁷ Lu or a cation of ⁶⁸ Ga.

36. The compound or salt of any of items 1 to 33, wherein the silicon-fluoride acceptor group is labeled with ¹⁸ F and the chelating group contains a chelated non-radioactive cation or is free of a chelated cation.

37. A pharmaceutical composition comprising or consisting of one or more compounds or salts of any of items 1 to 36. 38. The compound or salt of any of items 1 to 36 for use as a medicament.

39. The compound or salt of any of items 1 to 36 or the pharmaceutical composition of item 37 for use in the treatment or prevention of cancer, wherein the cancer is preferably neuroendocrine tumor.

40. A diagnostic composition comprising or consisting of a compound or salt of any of items 1 to 36.

41 . The compound or salt of any of items 1 to 36 or the diagnostic composition of item 40 for use in a method of diagnosis in vivo of a disease or disorder.

42. The compound or salt or the diagnostic composition for use of item 41, wherein the disease or disorder is cancer, and wherein the cancer is preferably neuroendocrine tumor.

43. The compound or salt or the diagnostic composition for use of item 41 or 42, wherein the method of diagnosis involves nuclear diagnostic imaging, wherein the nuclear diagnostic imaging is preferably positron emission tomography or single photon emission computerised tomography imaging.

In this specification, a number of documents including not only scientific journal articles but also patent applications and manufacturer’s manuals are cited (cf, e.g., the list of references below in this respect). The disclosure of these documents, while not considered relevant for the patentability of this invention, is herewith incorporated by reference in its entirety. More specifically, all referenced documents are incorporated by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.

Abbreviations

2-CTC ^■ 2-Chlorotrityl chloride

Acm ^■ Acetamidomethyl

AR42J ^■ Rat exocrine pancreatic tumour

Arg ^■ Arginine

Asp ^■ Aspartic acid

BA ^■ Benzoic acid

Boc ^■ tert-Butoxycarbonyl

BSA ^■ Bovine Serum Albumine

CHO ^■ Chinese hamster ovary

CT ^■ Computed tomography Cys · Cysteine d ^■ D-lsomer, Doublet

DCM · Dichloromethane

Dde ^■ 2-Acetyldimedone

DIPEA ^■ N,N-Diisopropylethylamine

DM EM/ F -12 ^■ Dulbecco ^' s Modified Eagle Medium/Nutrient Mixture F-12 DMF ^■ Dimethylformamide DMSO ^■ Dimethyl sulfoxide eq ^■ Equivalent

ESI-MS ^■ Electrospray ionization mass spectrometry

FCS ^■ Fetal Calf Serum, Fetal Calf Serum

Fmoc ^■ Fluorenylmethyloxycarbonyl

GBq ^■ Gigabecquerels

Gly ^■ Glycine

GP ^■ General Procedure

HATU · Hexafluorophosphate Azabenzotriazole Tetramethyl Uronium HBSS ^■ Flank ^' s Balanced Salt Solution HBSS-B ^■ HBSS with 1% BSA

HEPES ^■ 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid

HFIP ^■ Hexafluoro-2-propanol

HOAt ^■ 1 -Hydroxy- 7-azabenzotri azole

HOBt · Hydroxybenzotriazole

HPLC ^■ High Performance Liquid Chromatography

HSA ^■ Human Serum Albumine

IC ₅₀ ^■ half maximal inhibitory concentration

J ^■ Spin-spin coupling

K _av ^■ Partition coefficient

I ^■ L-lsomer, Loading density

Lys ^■ Lysine

M ^■ Molecular weight m/z ^■ Mass-to-charge ratio

MBq ^■ Megabecquerels m _exact ^■ Calculated exact mass m _found ^■ Experimentally determined mass

MHz ^■ Megahertz n ^■ Number of experiment repetitions nm ^■ Nanomolar, Nanometer NMP ^■ N-Methylpyrrolidone 01 ^■ Optical imaging Orn ^■ Ornithine p ^■ Para

PBS ^■ Phosphate Buffered Saline

PCC · Pyridinium chlorochromate

PEG ^■ Polyethylene glycol

PET ^■ Positron emissuin tomography

PG ^■ Protecting group

Phe ^■ Phenylalanine

PLL ^■ Poly-L-lysine

Pma ^■ Phosphonomethylalanine ppm ^■ Parts per million

Rf ^■ Retention factor

RP ^■ Reversed Phase

RT · Room temperature s ^■ Singlet SiFA ^■ Silicon Fluoride Acceptor

SPECT ^■ Single photon emission computed tomography

SST ^■ Somatostatin receptor type 2

TA TE ^■ TyH-Octreotate

TBDMS ^■ tert-Butyldimethylsilyl

TBq ^■ Terrabecquerels

TBTU ^■ Hexafluorophosphate Benzotriazole Tetramethyl Uronium tBu ^■ tert-Butyl

TFA ^■ Trifluoroacetic acid

THF ^■ Tetrahydrofuran

Thr ^■ Threonine

TIPS ^■ Triisopropylsilane

TLC ^■ Thin layer chromatography

TOC ^■ Octreotid

IR ^■ Retention time

TRIS ^■ Tris(hydroxymethyl)aminomethane

Trp ^■ Tryptophan

Tyr ^■ Tyrosine

UV/VIS ^■ Ultraviolet/Visible v/v ^■ Percentage by volume

Vo ^■ Void volume

V _e ^■ Elution volume

Vol-% ^■ Percentage by volume

Xaa ^■ Amino acid

Y ^■ Gamma d ^■ Chemical shift in ppm

Examples

I. Materials and Methods

1 . General Methods 1.1 Reagents, Solvents and radioactive Isotopes

The reagents and solvents were used without further purification. The used solvents were purchased from VWR International (Buchsal, Germany) or Sigma Aldrich (Munich, Germany). Water for the HPLC-solvents was obtained from the in-house Millipore-system from Thermo Fischer Scientific Inc. (Waltham MA, USA), while Tracepure water derived from the company Merck Millipore (Darmstadt, Germany). Amino acids were purchased from IRIS Biotech GmbH (Marktredewitz, Germany), Sigma-Aldrich (Munich, Germany), Carbolution Chemicals GmbH (St. Ingbert, Germany), Merck Millipore (Darmstadt, Germany). Resins were purchased from IRIS Biotech GmbH (Marktredewitz, Germany) or CEM (Matthews, USA). Coupling reagents and other chemicals derive from Sigma-Aldrich (Munich, Germany), Molekula GmbH (Garching, Germany), CEM (Matthews, USA) and Macrocyclics Inc. (Dallas, USA). Chemicals for synthesis were purchased from the company Sigma-Aldrich (Munich, Germany) and Merck KGaA (Darmstadt, Germany). The used chelators derived from CheMatech (Dijon, France). Radioactive labeling with ¹²⁵ l was performed with a [ ¹²⁵ l]Nal solution in 40 mM NaOH (74 TBq/mmol) from HARTMANN ANALYTIC GmbH (Braunschweig, Deutschland). ¹⁸ F for radioactive labeling was received from Klinikum Rechts der Isar (Technische Universitat Munchen, Munchen, Deutschland). Biochemicals as cell mediums, PBS and Trypsin were bought from Biochrom GmbH (Berlin) and Sigma-Aldrich (Miinchen, Deutschland)

1.2 Instruments and Analytics 1.2.1 RP-HPLC System

Reaction- and quality-controls were conducted via analytical RP-HPLC. For this purpose, a linear gradient of MeCN (0.1% TFA, 2% H2O; v/v) in H2O (0.1% TFA; v/v) was run. The respective gradients can be taken from the synthesis instructions. The detection was conducted via an UV/VIS-detector at l= 220 nm or l=254 nm. All RP-HPLC chromatograms were evaluated using the LabSolutions Software from the Shimadzu Corp. (Kyoto, Japan). For the analytical studies following systems have been used:

Shimadzu Corp. (Kyoto, Japan): Consisting of two LC-20AD gradient-pumps, a CBM-20A communication module, a CTO-20A column oven, a SPD-20A UV/VIS-detector and a MultoKrom 100-5 Cis-column (5 pm, 125 ^c 4.6 mm, CS Chromatographie GmbH, Langerwehe, Germany) with a flow of 1 mL/min.

The complete purification of intermediate and end products was performed via semipreparative RP-HPLC. Here again a linear gradient of MeCN (0.1% TFA, 5% H2O; v/v) in H2O (0.1% TFA; v/v) was run. The respective gradients can be taken from the synthesis instructions. The detection was conducted via an UV/VIS-detector at l=220 nm or l=254 nm. All RP-HPLC chromatograms were evaluated using the LabSolution Software from the Shimadzu Corp. (Kyoto, Japan). For preparative purification two systems of the Shimadzu Corp. (Kyoto, Japan) have been used:

Shimadzu Corp. (Kyoto, Japan): Consisting of two LC-20AP gradient-pumps, a DGU-20A degassing unit, a CBM-20A communication module, a CTO-20 A column oven, a SPD-20A UV/VIS-detector and a MultoKrom 100-5 Cis-column (5 pm, 250 * 10 mm, CS Chromatographie GmbH, Langerwehe, Germany) with a flow of 5 mL/min.

Shimadzu Corp. (Kyoto, Japan): Consisting of two LC-20AT gradient-pumps, a DGU-20A degassing unit, a CBM-20A communication module, a SPD-20A UV/VIS-detector and a MultoKrom 100-5 C ₁₈ -column (5 pm, 250x10 mm, CS Chromatographie GmbH, Langerwehe, Germany) with a flow of 5 mL/min. 1.2.2 ESI-MS Spectrocopy

Mass spectrometry was performed using an Expression CMS Quadrupole device from the company Advion Inc. (Ithaca, USA).

1.2.3 Flash-Chromatography

Flash-chromatographic purifications were conducted at an Isolera™ Prime System from the company Biotage (Uppsala, Sweden) with a Biotage 09474 Rev. E Bio pump from the same company. For purification a linear gradient of MeCN (0.1% TFA, 2% H O; v/v) in H O (0.1% TFA; v/v) was run. Furthermore, a Biotage™ SNAP KP-C-m cartridge (12 g cartridge material, pore diameter: 93 A, surface: 382 m ² /g from the company Biotage (Uppsala, Sweden) was used.

1.2.4 Lyophilisation

The lyophilization of intermediate- and end-products was conducted at an Alpha 1-2 lyophilization instrument from the company Christ (Osterode am Harz, Germany) using a RZ-2 vacuum-pump from Vacubrand GmbH. The substance to be dried was dissolved beforehand in H O and fBuOH (1/1 ; v/v ) and the solution was frozen at -80° C.

1.2.5 NMR

¹ H- and ¹³ C-NMR spectra were recorded on a Bruker ( Billerica , Massachusetts, USA) AVHD- 300 or AVHD-400 at 300 K. ¹ H and ¹³ C chemical shifts are reported in ppm and referenced to the residual proton of the solvent. Deuterated solvents were obtained from Sigma Aldrich.

2. Organic Synthesis

2.1 Synthesis of SiFA-Br and SiFA-BA

Scheme 1: General strategy for the synthesis of SiFA-bromide (SiFA-Br) and SiFA-acetic acid (SiFA-BA). ((4-Bromobenzyl)oxy)(fert-butyl)dimethylsilane (B2)

B2

In a round bottom flask, 4.68 g of 4-Bromobenzyl alcohol (B1, 25.0 mmol, 1.00 eq.) are dissolved and stirred in 70 ml_ dry DMF. 2.04 g of imidazole (30.0 mmol, 1 .20 eq.) and 4.52 g TBDMS-chloride (30.0 mmol, 1.20 eq.) are added under stirring. The mixture is left for reaction for 20 h at room temperature. The reaction is then poured into 250 mL of ice-cold H2O and the organic phase is extracted with Et ₂ 0 (5 * 50 mL). The combined organic phases are washed with a saturated aqueous solution of NaHC0 ₃ (100 mL), brine (100 mL) and dried over Na2SC>4. The solvent is removed under reduced pressure and the crude product is purified via column chromatography (5% EtOAc in petroleum ether). After the solvents are removed under reduced pressure, 7.24 g of the product B2 (24.1 mmol, 96%) are yielded as a colorless oil.

TLC (S1O2, 5% EtOAc/petroleum ether): R _f = 0.97 [UV]

¹ H-NMR (300 MHz, CDCI ₃ ): d [ppm] = 7.45 (d, ³ J = 8 Hz, 2 H, H _Ar ), 7.20 (d, ³ J = 8 Hz, 2 H, H _Ar ), 4.68 (s, 2 H, Ar-CH ₂ ), 0.94 (s, 9 H, C-CH ₃ ), 0.10 (s, 6 H, Si-CH ₃ ).

¹³ C-NMR (75 MHz, CDCI ₃ ): d [ppm] = 140.3 (s, Q), 130.1 (s, C _m ), 127.5 (s, C ₀ ) 120.4 (s, C _P ), 64.2, (s, CH ₂ ), 25.8 (s, C-CH ₃ ), 18.2, (s, C-CH ₃ ) 5.4 (s, Si-CH ₃ ).

Di-fert-butyl(4-(((ferf-butyldimethylsilyl)oxy)methyl)phe nyl)fluorosilane (B3)

B3

In an argon atmosphere, 7.24 g B2 (24.1 mmol, 1.00 eq.) are dissolved in 67 mL dry THF and cooled to -78 °C (dry ice and acetone). Over a period of 1.5 h, 32.6 mL of a 1.7 M solution of fBuLi in pentane (55.4 mmol, 2.30 eq.) are slowly dropped to the solution of B2 in THF. The mixture is left for stirring at -78 °C for an additional 30 min. In another round bottom flask, 5.00 g of di-te/t-butyldifluorosilane (27.7 mmol, 1 .10 eq.) are dissolved in 44 mL of dry THF and also cooled to -78 °C. Over a period of 2 h and under constant stirring, the mixture of B2 and fBuLi in THF is slowly dropped to the solution of di-te/t-butyldifluorosilane. The reaction is allowed to warm to room temperature and is left under stirring for another 15 h. Through addition of 120 mL of brine the reaction is terminated and the organic phase is separated. The aqueous phase is extracted with Et ₃ 0 (3 * 100 mL), the combined organic phases are dried over MgSCL and the solvents are removed under reduced pressure. The product B3 is yielded as a yellowish oil (9.14 g, 23.9 mmol, 99%).

¹³ C-NMR (75 MHz, CDCI ₃ ): d [ppm] = 143.0 (s, C), 134.1 (d, ³ J ( ¹³ C, ¹⁹ F) = 12 Hz, C _m ), 132.0 (d, ² J ( ¹³ C, ¹⁹ F) = 56 Hz, Cp), 125.3 (s, C ₀ ), 65.0 (s, CH ₂ ), 27.5 (s, CH ₃ ), 26.8 (s, C-CH ₃ ), 26.1 (s, CH ₃ ), 20.4 (d, ² J ( ¹³ C, ¹⁹ F) = 8 Hz, C-CH ₃ ), 5.11 (s, Si-CH ₃ ).

(4-(Di-ferf-butyIfluorosiIyl)phenyI)methanoI (B4)

B4

Compound B3 (9.14 g, 23.9 mmol, 1.00 eq.) is dissolved in 50 rriL MeOH. After the addition of 3.00 ml_ of concentrated HCI (97.9 mmol, 4.10 eq.) the solution is left for reaction for 18 h at room temperature. The mixture is concentrated under reduced pressure, the precipitate is dissolved in 50 ml_ of Et2<D and the organic phase is washed with 50 mL of a saturated, aqueous solution of NaHCC>3. The aqueous phase is extracted with Et20 (3 ^c 50 mL), the combined organic phases are combined and dried over MgSCXi. The solvents are removed under reduced pressure and the product B4 (5.90 g, 22.0 mmol, 92%) is yielded as a yellowish oil.

¹ H-NMR (CDCb): d [ppm] = 7.61 (d, 2 H, ³ J = 8 Hz, H _Ar ), 7.38 (d, 2 H, ³ J = 8 Hz, H _Ar ), 4.72 (s, 2 H, Ar-CH ₂ ), 1.06 (s, 18 H, C-CH ₃ ).

¹³ C-NMR (CDCI ₃ ): d [ppm] = 142.3 (s, C), 134.4 (d, ³ J( ¹³ C, ¹⁹ F) = 12 Hz, C _m ), 133.1 (d, ² J( ¹³ C, ¹⁹ F) = 56 Hz, C _p ), 125.6 (s, C ₀ ), 65,4 (s, CH ₂ ), 27.4 (s, CH ₃ ), 20.4 (d, ² J ( ¹³ C, ¹⁹ F) = 8 Hz, C- CH ₃ ).

HPLC (50-100 % B in 15 min) t _R = 10.7 min 4-(Di-ferf-butyifluorosilyl)benzaldehyde (B5)

B5

The Alcohol B4 (5.90 g, 55.0 mmol, 2.5 eq.) is dissolved in 60 mL dry DCM and slowly dropped to an ice-cold solution of 11.9 g PCC (55.0 mmol, 2.5 eq.) in 180 mL DCM. The solution is stirred for 30 min at 0 °C and another 4 h at room temperature. The reaction is terminated through the addition of 60 mL of Et20 and the supernatant is decanted. The insoluble, black residue is washed thoroughly with Et and the combined organic phases are filtered over a short silica plug. Solvent removal under reduced pressure is followed by purification via column chromatography (2.5% EtOAc in petroleum ether). Product B5 is yielded as yellowish oil, slowly crystallizing to a yellowish solid (2.22 g, 8.33 mmol, 36%).

¹ H-NMR (CDCI3): d [ppm] = 10.1 (s, 1 H, CHO), 7.88 (d, ³ J = 6 Hz, 2 H, H _Ar ), 7.79 (d, ³ J = 9 Hz, 2 H, H _Ar ), 1.07 (s, 18 H, C-CH ₃ ).

¹³ C-NMR (CDCI3): d [ppm] = 192.7 (s, CHO), 142.5 (s, O), 137.2 (s, C _p ), 134.7 (d, 3J ( ¹³ C, ¹⁹ F) = 12 Hz, C _m ), 128.6 (s, C ₀ ), 27.4 (s, CH ₃ ), 20.5 (s, C-CH ₃ ).

¹⁸ F-NMR (CDCb) = d [ppm] = 188.4 (s, F).

HPLC (50-100 % B in 15 min) t _R = 15.9 min.

4-(Di-ferf-butylfluorosilyl)benzoic acid (SiFA-BA)

SiFA-BA

The aldehyde B5 (1.0 eq.) is dissolved in fBuOH (23 mL/g starting material), DCM (2.5 mL/g starting material) and Nah^PCl» * H O (1.25 M, pH = 4.0 - 4.5, 15 ml_/g educt) and KMn _aq. (1 M, 23 mL/g starting material) is added. After stirring for 25 min, the mixture is cooled to 5 °C. KMnCL (1.0 eq.) is added and the reaction quenched shortly afterwards by addition of of a saturated, aqueous solution of NaHCCh. The mixture is dried over MgS0 ₄ and the solvent evaporated under reduced pressure. The crude product is purified by recrystallization from Et ₂ 0/n-hexane (1/3 v/v) and SiFA-BA is afforded as a colorless solid (60% yield).

¹ H-NMR (300 MHz, CDCI ₃ ): d [ppm] = 8.10 (d, ³ J = 8.1 Hz, 2 H, H _m ), 7.74 (d, ³ J = 8.1 Hz, 2 H, H _o ), 1.07 (s, 18 H, CCH ₃ ).

¹³ C-NMR (75 MHz, CDCI ₃ ): d [ppm] = 171.0 (s, COOH), 141.4 (d, C _p ), 134.2 (d, C _m ), 129.0 (d, C _;o ), 27.4 (s, CCH ₃ ), 20.4 (d, CCH ₃ ).

RP-HPLC (50-100 % in 15 min) t _R = 8.4 min.

(4-(Bromomethyl)phenyl)di-tert-butylfluorosilane (SiFA-Br)

SiFA-Br

To a 0 °C cooled solution of B4 (3.08 g, 11.5 mmol, 1.0 eq.) and tetrabromomethane (4.18 g, 12.6 mmol, 1.1 eq.) in 100 mL DCM, triphenylphosphine (3.30 g, 12.6 mmol, 1.1 eq.) was added over a period of 30 min in small portions. The solution was stirred for 2 h at room temperature. Solvents were removed in vacuo and the residue was washed with cold n- hexane (3 x 50 mL). A white precipitate was removed by filtration and the solution was concentrated in vacuo. Purification was conducted by flash column chromatography (silica, 5 % EtOAc in petrol, v/v). Compound SiFA-Br was isolated as a colorless oil (3.06 g, 9.20 mmol, 80%). RP-HPLC (50 to 100% B in 15 min): t _R = 9.2 min, K’ = 3.73.

¹ H-NMR (400 MHz, CDCI ₃ ): d [ppm] = 7.58 (2 H, d, C ₆ H ₄ ), 7.40 (2 H, d, C ₆ H ₄ ), 4.49 (2 H, s, CH ₂ OSi), 1.05 (18 H, s, Si(fBu) ₂ ).

3. Peptide Synthesis

3.1 General Procedures (GP)

3.1.1 General Procedures for Solid-Phase-Peptide-Synthesis (SPPS)

By means of the solid phase peptide synthesis via Fmoc-strategy, peptides are synthesized on a resin, whereby Fmoc is used as temporary protective group. The resin is loaded with a Fmoc-protected amino acid (Xaa), subsequently it is Fmoc-deprotected and brought to reaction with the next amino acid. After completion of the aspired peptide, it is split off the resin. Before peptide elongation, cleavage of protecting groups or any other type of chemical modification, the already loaded resin has to be swollen for 30 min in a suitable solvent (DMF, DCM, NMP). After each reaction step, the resin has to be washed thoroughly, with the solvent used for the reaction. If no further reaction step is conducted, the resin has to be washed with DCM and dried in vacuo. GP1: 2-CTC-resin Loading

Loading of the 2-Chlorotritylchloride resin (2-CTC) with a Fmoc-protected amino acid (Fmoc- Xaa-OH) is carried out by stirring a suspension of the 2-CTC-resin (1.60 mmol/g and Fmoc- Xaa-OH (0.70 eq.) in DMF with DIPEA (4.5 eq.) at room temperature for 4 h. Remaining tritylchloride is capped by addition of methanol (2 mL/g resin) for 15 min. Subsequently the resin is filtered and washed with DMF (5 x 5 ml_/g resin), methanol (3 x 5 mL/g resin) and dried in vacuo. Final loading I of Fmoc-Xaa-OH is determined by the following equation:

GP2: On-resin Peptide Formation

The respective side-chain protected Fmoc-Xaa-OH (1.5 eq.) is dissolved in DMF (8 mL/g resin) and pre-activated by adding TBTU or HATU (1.5 eq.), HOBt or FIOAt (1.5 eq.) and DIPEA (4.5 eq.) or 2,4,6-collidine (5.5 eq.). The solution is left for pre-activation for 10 min, followed by addition to the resin-bound peptide NH ₂ -(Xaa) _x -2-CT and shaken for 2 h at room temperature. In case of amino acids, sensible to racemization (e.g. Dap, Cys), the pre-activation time is strictly limited to 2 min and 2,4,6-collidine is used as base. Subsequently, the resin is washed with DMF (6 x 5 mL/g resin) and after Fmoc-deprotection the next amino acid is coupled analogously. The coupling of non-aminoacidic building blocks (SiFA-BA etc.) is carried out following the same protocol.

GP3: On-resin Chelator Conjugation

The chelator (1.5 eq.) (e.g. DOTA(fBu)3, R/S-DOT AGA(fBu )4) is dissolved in DMF (8 mL/g resin) and pre-activated by adding FIATU (1.5 eq.), FIOAT (1.5 eq.) and DIPEA (4.5 eq.). After pre-activation for 10 minutes, the solution is added to the resin bound peptide F½N-(Xaa) _x -2- CT and shaken for 6 to 18 h. Completeness of the reaction has to be confirmed by RP-HPLC and ESI-MS. Subsequently, the resin is washed with DMF (6 x 5 mL/g resin).

GP4: On-resin Fmoc-deprotection

The resin-bound Fmoc-peptide is treated with 20% piperidine in DMF (v/v, 8 mL/g resin) for 5 min and subsequently for 15 min. Afterwards, the resin is washed thoroughly with DMF (8 x 5 mL/g resin). GP5: On-resin Dde-deprotection

Dde-deprotection is performed by adding a solution of imidazole (0.46 g), hydroxylamine hydrochloride (0.63 g) in NMP (2.5 mL) and DCM (0.5 ml_) for 3 h at room temperature. After deprotection the resin is washed with DMF (6 ^c 5 mL/g resin).

GP6: Peptide Cleavage from the Resin (Preservation of Acid labile Groups)

The resin-bound peptide is cleaved and dissolved in a mixture of HFIP/DCM (v/v; 4/1, 8 ml_/g resin) and shaken for 45 min. The solution containing the fully protected peptide is filtered off and the resin is treated with another portion of the cleavage solution for 45 min. Both fractions are combined and the solvents are removed in vacuo. After lyophilisation in /BUOH/H2O, the crude, fully protected peptide is obtained.

GP7: Peptide Cleavage from the Resin (Deprotection of all Acid labile Groups)

The fully protected resin-bound peptide is dissolved in a mixture of TFA/TIPS/H2O (v/v/v, 90/2.5/7.5) and shaken for 45 min. The solution is filtered off and the resin is treated in the same way for another 45 min. Complete deprotection is achieved by combining both filtrates and incubation at 40 °C for 1 h and at room temperature for 2 h (no chelator with fBu-proteeting groups apparent the peptide) or 12 h (chelator with iBu-protecting group e.g. DOTA(fBu)3 apparent in the peptide). After concentration under a stream of nitrogen, the crude product is dissolved in a mixture of ferf-butanol and water followed by subsequent lyophilisation to obtain the crude peptide.

GP8: Reaction Control via Test-Cleavage

To verify the completeness of an amino acid coupling or any other kind of chemical modification, a small portion of resin is transferred into a 1.5 mL reaction tube and treated with the under GP6 and GP7 described solutions to either obtain the protected (in the following described as mild test cleavage) or unprotected (in the following described as harsh test cleavage) peptide. After concentration under a stream of nitrogen the remains are dissolved in RP-HPLC solvent and therefore suitable for RP-HPLC and ESI-MS investigation.

3.1.2 General Procedures for Synthesis in Solution

GP9: Formation of [ ^nat Ga] Complexes

The ligand is dissolved in DMSO at a 2 mM concentration. Since the solvents for the purification via semi-preparative RP-HPLC are acidified with TFA, the formation of TFA salts is assumed and included in the molecular weight. For complexation, a defined volume of the peptide solution is mixed with 1.5 eq. of [ ^nat Ga]Ga(NOs)3 in H2O (20 mM). DMSO is added to generate a final concentration of 1 mM. The solution is left at 70 °C for 40 min and the stoichiometric conversion of the chelator is confirmed by RP-HPLC and ESI-MS.

GP10: Formation of [ ^nat Lu] Complexes

The ligand is dissolved in DMSO at a 2 mM concentration. Since the solvents for the purification via semi-preparative RP-HPLC are acidified with TFA, the formation of TFA salts is assumed and included in the molecular weight. For complexation, a defined volume of the peptide solution is mixed with 1.5 eq. of [ ^nat Lu]LuCl ₃ in H2O (20 mM). DMSO is added to generate a final concentration of 1 mM. The solution is left at 70 °C for 40 min and the stoichiometric conversion of the chelator is confirmed by RP-HPLC and ESI-MS.

GP11: Formation of [ ^nat Pb] Complexes

The ligand is dissolved in DMSO at a 2 mM concentration. Since the solvents for the purification via semi-preparative RP-HPLC are acidified with TFA, the formation of TFA salts is assumed and included in the molecular weight. For complexation, a defined volume of the peptide solution is mixed with 1.1 eq. of [ ^nat Pb]PbCh in H2O (10 mM). DMSO is added to generate a final concentration of 1 mM. The solution is left at 70 °C for 40 min and the stoichiometric conversion of the chelator is confirmed by RP-HPLC and ESI-MS.

3.2 Synthesis of Building Blocks

Synthesis of SiFA-BA-D-Asp-Offiu (B6)

The on-resin synthesis of SiFA-BA-D-Asp-OfBu (B6) is carried out applying general procedures GP1, GP2, GP4 and GP6. Briefly, Fmoc-D-Asp-OfBu (0.7 eq.) is loaded onto 2- CTC resin (1.0 eq.; loading capacity 1.6 mmol/g). After Fmoc-deprotection, SiFA-BA (1.5 eq.) is conjugated, applying HO At (1.5 eq.), TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). To separate the peptide from the resin under preservation of the fBu-protecting group, the resin is treated with HFIP/DCM ( v/v, 4/1 , 8 mL/g resin) as described in GP6. After final lyophilisation, crude product B6 is yielded as colorless solid. Correct product formation is confirmed by RP- HPLC and ESI-MS.

RP-HPLC (10 - 90% in 15 min): t _R = 17.1 min. ESI-MS: rO _exacf (C19H2 ₈ FNO5S1): 397.2; mf _0U nd ^' · m/z = 398.2 [M+H] ⁺ .

Scheme 2: Strategy for the synthesis of B6. a) 2-CTC resin, DIPEA, Fmoc-D-Asp-OfBu (DMF); b) Fmoc-deprotection: 20% piperidine in DMF; c) SiFA-BA, HOAt, TBTU, 2,4,6-collidine (DMF); d) HFIP (DCM).

Synthesis of Boc-D-Om(Boc)-D-Orn(Boc)-OH (B7)

The on-resin synthesis of Boc-D-Orn(Boc)-D-Orn(Boc)-OH (B7) is carried out applying general procedures GP1 , GP2, GP4 and GP6. Briefly, Fmoc-D-Orn(Boc)-OH (0.7 eq.) is loaded onto 2-CTC resin (1.0 eq.; loading capacity 1.6 mmol/g). After Fmoc-deprotection, Boc-D-Orn(Boc)- OH (1.5 eq.) is conjugated, applying HOAt (1.5 eq.), TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). Mild peptide cleavage from the resin is carried out according to GP6. After final lyophilisation, crude product B7 is yielded as colorless solid. Correct product formation is confirmed by RP-HPLC and ESI-MS.

Scheme 3: Strategy for the synthesis of B7. a) 2-CTC resin, DIPEA, Fmoc-D-Orn(Boc)-OH (DMF); b) Fmoc-deprotection: 20% piperidine in DMF; c) Fmoc-D-Orn(Boc)-OH, HOAt, TBTU, 2,4,6-collidine (DMF); d) HFIP (DCM). 3.3 Synthesis of the Binding Motifs 3.3.1 Tyr ³ - Octreotate (TATE or X1 )

Peptide Sequence

The on-resin synthesis of fully protected TATE is carried out analogously to published protocols applying general procedures GP1 , GP2 and GP4 [19, 25], Briefly, Fmoc-L-Thr(fBu)-OH (0.7 eq.) is loaded to 2-CTC resin (1.0 eq.; loading capacity 1.6 mmol/g), followed by Fmoc-deprotection and subsequent coupling of Fmoc-L-Cys(Acm)-OH, Fmoc-L-Thr(fBu)-OH, Fmoc-

L-Lys(Boc)-OH, Fmoc-D-Trp(Boc)-OH, Fmoc-L-Tyr(fBu)-OH, Fmoc-L-Cys(Acm)-OH and Fmoc-D-Phe-OH. For the conjugation of all amino acids the following protocol is applied: Fmoc- Xaa-OH (1.5 eq.), HO At (1.5 eq.), TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). The Fmoc protecting group of the last amino acid remains until the disulfide bridge is formed.

Disulfide-bridge formation [19, 25-27]

Fmoc-D-Phe-L-Cys(Acm)-L-Tyr(fBu)-D-Trp(Boc)-L-Lys(Boc)-L- Thr(fBu)-L-Cys(Acm)-L- Thr(fBu)-2-CT (1.0 eq.) is treated with TI(TFA)3 (4.0 eq.) in DMF for 45 min. After discarding the first solution the procedure is repeated with a new portion of TI(TFA)3, for another 45 min. The resin is washed with DMF (6 * 5 mL/g resin) and completeness of cyclization is verified by RP-HPLC and ESI-MS (test cleavage: TFA/H2O/TIPS 90/2.5/7.5) confirming the synthesis of Fmoc-D-Phe-cyc/o[L-Cys-L-Tyr(fBu)-D-Trp(Boc)-L-l_ys(Boc)-L-T hr(fBu)-L-Cys]-L-Thr(fBu)-2- CT. Finally, the peptide is Fmoc-deprotected leading to H-TATE(PG)-2-CT (X1).

RP-HPLC (10 - 90% in 15 min): t _R = 10.8 min.

ESI-MS: m _e xacf (C64H74N10O14S2): 1270.5; vrifou _nd' · m/z = 1273.4 [M+H] ⁺ .

Scheme 4: Strategy for the synthesis of H-TATE(PG)-2-CT (X1), All amino acid conjugations are carried out applying HOAt, TBTU, 2,4,6-collidine (DMF). Fmoc-deprotection (20% piperidine in DMF) is implied after every coupling, a) Fmoc-L-Thr(fBu)-OH, DIPEA (DMF); b) Fmoc-L-Cys(Acm)-OH; c) Fmoc-L-Thr(fBu)-OH; d) Fmoc-L-Lys(Boc)-OH; e) Fmoc-D-Trp(Boc)- OH; f) Fm oc-L-Ty r( fB u )-0 H ; g) Fmoc-L-Cys( Acm )-OH ; h) Fmoc-L-Phe-OH; i) TI(TFA)3 (DCM). The on-resin synthesis of fully protected JR11 (X25) is carried out analogously to the synthesis described for X1 applying general procedures GP2 and GP4. In contrast to the synthesis described for TATE based peptides, the here applied resin is the Rink-amide resin. A specific loading protocol is not needed for this type of resin, therefore the first amino acid (Fmoc-D-Tyr(fBu)-OH, 1.5 eq.) is directly conjugated applying HOAt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (4.0 eq.). Followed by Fmoc-deprotection and subsequent coupling of Fmoc-L- Cys(Acm)-OH, Fmoc-L-Thr(/Bu)-OH, Fmoc-L-Lys(Boc)-OH, Fmoc-D-Aph(Cbm)-OH, Fmoc-L- Aph(Hor)-OH, Fmoc-D-Cys(Acm)-OH and Fmoc-L-Phe(4-CI)-OH. For the conjugation of all amino acids the following protocol is applied: Fmoc-Xaa-OH (1.5 eq.), HOAt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (4.0 eq.). The Fmoc protecting group of the last amino acid remains until the disulfide bridge is formed. The formation of the disulfide bridge is carried analogously to the synthesis described for X1. The completeness of the cyclization is verified by RP-HPLC and ESI-MS (test cleavage: TFA/H ₂ 0/TIPS 90/2.5/7.5) confirming the synthesis of Fmoc-L- Phe(4-CI)-cyc/o[D-Cys-L-Aph(Hor)-D-Aph (Cbm)-L-Lys(Boc)-L-Thr(fBu)-L-Cys]-D-Tyr(fBu)-rink- amide. Finally, the peptide is Fmoc-deprotected leading to H-JR11(PG)-2-CT (X25). RP-HPLC (10 - 90% in 15 min): t _R = 9.90 min.

ESI-MS: m _exaci (C77H90CIN15O1 ₆ S2): 1522.5; m _f0und : m/z = 763.7 [M+2H] ²⁺ , 1524.2 [M+H] ⁺ .

3.4 Synthesis of Ligands 3.4.1 Synthesis of Precursors

Synthesis of H-PEGi-TATE(PG)-2-CT (X4)

The synthesis of H-PEGi-TATE(PG)-2-CT (X4) is carried out applying GP2 and GP4. Briefly, resin bound X1 (1.0 eq.) is conjugated with Fmoc- 020C-0H (Fmoc-PEG-i-OH, 1.50 eq.) applying HO At (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). Final Fmoc-deprotection results in compound X4.

Synthesis of H-[Gly]i. ₃ -TATE(PG)-2-CT (X12, X5, X13)

The synthesis of H-Gly-TATE(PG)-2-CT (X12), H-Gly-Gly-TATE(PG)-2-CT (X5) and H-Gly- Gly-Gly-TATE(PG)-2-CT (X13), are carried out analogously, applying GP2 and GP4. Briefly, resin bound X1 (1.0 eq.) is conjugated once, twice or thrice with Fmoc-Gly-OH (1.5 eq.) applying HO At (1.5 eq.) TBTU (1 .5 eq.) and 2,4,6-collidine (5.5 eq.). Final Fmoc-deprotection results in compounds X12, X5, and X13.

Synthesis of H-L/D-Asn(Trt)-L/D-Asn(Trt)-TATE(PG)-2-CT (X6 and X16) The synthesis of H-L-Asn(Trt)-L-Asn(Trt)-TATE(PG)-2-CT (X6) and H-D-Asn(Trt)-D-Asn(Trt)- TATE(PG)-2-CT (X16) are carried out, applying GP2 and GP4. Briefly, resin bound X1 (1.0 eq.) is conjugated twice with Fmoc-L-Asn(Trt)-OH (1.5 eq.) or Fmoc-D-Asn(Trt)-OH (1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). Final Fmoc-deprotection results in compounds X6 and X16.

Synthesis of H-Gly-D-Asn(T rt)-D-Asn(T rt)-TATE(PG)-2-CT (X17)

The synthesis of H-Gly-D-Asn(Trt)-D-Asn(Trt)- TATE(PG)-2-CT (X17) is carried out, applying GP2 and GP4. Briefly, resin bound X1 (1.0 eq.) is conjugated twice with Fmoc-D-Asn(Trt)-OH (1.5 eq.) and once with Fmoc-Gly-OH, applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). Final Fmoc-deprotection results in compound X17.

H-D-Asp(fBu)-D-Asp(fBu)-PEGi-TATE(PG)-2-CT (X7)

The synthesis of H-D-Asp(fBu)-D-Asp(fBu)- PEGi-TATE(PG)-2-CT (X7), is carried out applying GP2 and GP4. Briefly, resin bound X4 (1.0 eq.) is conjugated twice with Fmoc-D- Asp(fBu)-OH (1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). Final Fmoc-deprotection results in

H-D-Asp(fBu)-D-Asp(fBu)-Gly-TATE(PG)-2-CT (X14)

Starting from resin bound X12, the synthesis of H-D- Asp(fBu)-D-Asp(fBu)-Gly-TATE(PG)-2-CT (X14) is carried out analogously to the synthesis of X7. All synthesis steps are transferable. H-D-Asp(fBu)-D-Asp(fBu)-Gly-Gly-TATE(PG)-2-CT (X8)

Starting from resin bound X5, the synthesis of H-D-Asp(fBu)-D-Asp(fBu)-Gly-Gly-TATE(PG)-2- CT (X8) is carried out analogously to the synthesis of X7. All synthesis steps are transferable.

H-D-Asp(fBu)-D-Asp(fBu)-Gly-Gly-Gly-TATE(PG)-2-CT (X15)

Starting from resin bound X13, the synthesis of H-D-Asp(fBu)-D-Asp(fBu)-Gly-GIy-Gly-

TATE(PG)2-CT (X15) is carried out analogously to the synthesis of X7. All synthesis steps are transferable.

H-D-Asp(fBu)-D-Asp(fBu)-L-Asn(Trt)-L-Asn(Trt)-TATE(PG)-2- CT (X9)

Starting from resin bound X6, the synthesis of H- D-Asp(fBu)-D-Asp(fBu)-L-Asn(T rt)-L-Asn(T rt)- TATE(PG)-2-CT (X9) is carried out analogously to the synthesis of X7. All synthesis steps are transferable.

H-D-Asp(fBu)-D-Asp(fBu)-D-Asn(Trt)-D-Asn(Trt)-TATE(PG)-2- CT (X18)

Starting from resin bound X16, the synthesis of H-D-Asp(fBu)-D-Asp(fBu)-D-Asn(Trt)-D-Asn(Trt)- TATE(PG)-2-CT (X18) is carried out analogously to the synthesis of X7. All synthesis steps are transferable. H-D-Asp(fBu)-D-Asp(fBu)-Gly-D-Asn(Trt)-D-Asn(Trt)-TATE(PG)-2 -CT (X19)

Starting from resin bound X17, the synthesis of H-D-Asp(fBu)-D-Asp(fBu)-D-Asn(T rt)-D-

Asn(Trt)-TATE(PG)-2-CT (X19) is carried out analogously to the synthesis of X7, All synthesis steps are transferable.

Synthesis of H-D-Orn(Boc)-D-Orn(Boc)-Gly-Gly-TATE(PG)-2-CT (X10)

Starting from resin bound X5, the synthesis of H- D-Orn(Boc)-D-Orn(Boc)-Gly-Gly-TATE(PG)-2-CT (X10) is carried out analogously to the synthesis of X7. In contrast to X7, instead of Fmoc-D- Asp(fBu)-OH, Fmoc-D-Orn(Boc)-OH is used as amino acid. All other steps are transferable.

Synthesis of H-D-Orn(Boc)-D-Orn(Boc)-Gly-Gly-Gly-TATE(PG)-2-CT (X23)

Starting from resin bound X13, the synthesis of H-D-Orn(Boc)-D-Orn(Boc)-Gly-Gly-Gly- TATE(PG)-2-CT (X23) is carried out analogously to the synthesis of X10. All Synthesis steps are transferable.

Synthesis of H-D-Asn(T rt)-D-Asn(T rt)-GIy-Gly-TATE(PG)-2-CT (X11)

Starting from resin bound X5, the synthesis of H- D-Asn(Trt)-D-Asn(Trt)-Gly-Gly-TATE(PG)-2-CT (X11) is carried out analogously to the synthesis of X7. In contrast to X7, instead of Fmoc-D- Asp(fBu)-OH, Fmoc-D-Asn(Trt)-OH is used as amino acid. All other steps are transferable. Synthesis of H-D-Asn(Trt)-D-Asn(Trt)-Gly-Gly-Gly-TATE(PG)-2-CT (X24)

Starting from resin bound X13, the synthesis of H-D-Asn(T rt)-D-Asn(T rt)-Gly-Gly-Gly-

TATE(PG)-2-CT (X24) is carried out analogously to the synthesis of X11. All synthesis steps are transferable.

Synthesis of H-D-Lys(Boc)-D-Asp(tBu)- D -Asp(tBu)-Gly-Gly-TATE(PG)-2-CT (X20), H-D- Cit-D-Asp(tBu)- D -Asp(tBu)-Gly-Gly-TATE(PG)-2-CT (X21) and H-D-Glu(tBu)-D-Asp(tBu)- D -Asp(tBu)-Gly-Gly-TATE(PG)-2-CT (X22)

The synthesis of X20, X21 and X22 are carried out applying GP2 and GP4. Briefly, resin bound X15 (1.0 eq.) is conjugated with either Fmoc-D-Lys(Boc)-OH (1.5 eq.) or Fmoc-D-Cit-OH (1.5 eq.) or Fmoc-D-Glu(tBu)-OH (1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6- collidine (5.5 eq.). Final Fmoc-deprotection results in compounds X20, X21 and X22.

H-D-Asp(fBu)-D-Asp(fBu)-Gly-Gly-Gly-JR11 (PG)-rink-amide (X26) The synthesis of H-D-Asp(fBu)-D- Asp(fBu)-Gly-Gly-Gly-JR11 (PG)-rink- amide (X26), is carried out applying GP2 a ^nc · GP4. Briefly, resin bound X25 (1.0 eq.) is conjugated three times with Fmoc-Gly-OH and then twice with Fmoc-

D-Asp(fBu)-OH (1.5 eq.) applying HO At (1.5 eq.) TBTU (1.5 eq.) and DIPEA (4.0 eq.). Final Fmoc-deprotection results in compound X26. 3.4.2 Ligand Synthesis: Simple SiFA-Moiety

Synthesis of 1 (reference ligand)

The synthesis of the ligand 1 is carried out applying GP2, GP3, GP4, GP5 and GP7. Briefly, resin bound precursor X7 (1.0 eq.) is conjugated with Fmoc-D-Dap(Dde)- OH (1.5 eq.) applying HOBt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). After Dde- deprotection, SiFA-BA (1.5 eq.) is conjugated applying HOBt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (4.5 eq.). After Fmoc-deprotection, the N- terminus (1.0 eq.) is conjugated with the chelator rac-DOTAGA-anhydride (2.5 eq.), applying DIPEA (10.0 eq.) in DMF (8 mL/g resin) for 24 h at room temperature. The resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H2O, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvent is removed under reduced pressure. The precipitate is dissolved in fBuOH/H ₂ 0, frozen at -80 °C and final lyophilisation yields peptide 1 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): X _R = 11.8 min.

RP-HPLC (10 - 90% in 15 min): t _R = 10.9 min.

ESI-MS: nw (CwHwFNi^SzSi): 2231.9; nw: m/z = 745.3 [M+3H] ³⁺ , 1117.2 [M+2H] ²⁺ , 1489.4 [2M+3H] ³⁺ .

Synthesis of 3 (reference ligand)

Starting from precursor X7, the synthesis of ligand 3 is carried out analogously to the synthesis described for 1. In contrast to the synthesis of 1, DOTA- (fBu)3 (1.2 eq.) is used as chelator, applying HOBt (1.2 eq.), TBTU (1.2 eq.) and DIPEA (3.6 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 3 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): t _R = 10.7 min. RP-HPLC (10 - 90% in 15 min): t _R = 8.84 min.

ESI-MS: mexacf (C97H ₁₃ 8FNi903oS2Si): 2159.9; hn ₀ ^: m/z = 721.1 [M+3H] ³⁺ , 1081.1 [M+2H] ²⁺ , 1441.1 [2M+3H] ³⁺ .

Synthesis of 6 (reference ligand)

Starting from precursor X8, the synthesis of ligand 6 is carried out analogously to the synthesis described for 1. All synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP- HPLC, yielding peptide 6 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): t _R = 10.5 min.

RP-HPLC (10 - 90% in 15 min): t _R = 8.67 min.

ESI-MS: rrw _f (C98H137FN20O31S2S1): 2200.9; m r _ound, m/z = 735.2 [M+3H] ³⁺ , 1101.9 [M+2H] ²⁺ , 1468.4 [2M+3H] ³⁺ .

Synthesis of 8 (reference ligand)

Starting from precursor X8, the synthesis of ligand 8 is carried out analogously to the synthesis described for 1. In contrast to the synthesis of 1, DOTA(fBu) ₃ (1.2 eq.) is used as chelator, applying HOBt (1.2 eq.), TBTU (1.2 eq.) and DIPEA (3.6 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 8 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): t _R = 10.7 min.

RP-HPLC (10 - 90% in 15 min): t _R = 8.74 min.

ESI-MS: m _exaci (C ₉ 5Hi ₃ 3FN2o029S ₂ Si): 2128.9; rrV _c W m/z = 711.3 [M+3H] ³⁺ , 1065.7 [M+2H] ²⁺ . Synthesis of 2 (reference ligand) tion, SiFA-BA (1.5 eq.) is conjugated applying HOBt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (4.5 eq.). After Dde-deprotection, the A/-terminus (1.0 eq.) is conjugated with the chelator rac- DOTAGA-anhydride (2.5 eq.), applying DIPEA (10.0 eq.) in DMF (8 mL/g resin) for 24 h at room temperature. The resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H ₂ 0, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvent is removed under reduced pressure. The precipitate is dissolved in fBuOH/H ₂ 0, frozen at -80 °C and final lyophilisation yields peptide 1 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): t _f? = 11.5 min.

RP-HPLC (10 - 90% in 15 min): t _R = 10.7 min.

ES!-MS: m _exacf (CiooHi ₄₂ FNi ₉ 0 ₃₂ S ₂ Si): 2231.9; m _fol W m/z = 745.3 [M+3H] ³⁺ , 1117.2 [M+2H] ²⁺ , 1489.4 [2M+3H] ³⁺ .

Synthesis of 4 (reference ligand) other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 4 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): t* = 10.6 min. RP-HPLC (10 - 90% in 15 min): t _R = 8.83 min.

ESI-MS: rf) exact (C97H138FN19O30S2S1): 2159.9; m w m/z = 721.1 [M+3H] ³⁺ , 1081.1 [M+2H] ²⁺ , 1441.1 [2M+3H] ³⁺ .

Synthesis of 7 (reference ligand) semi-preparative RP-HPLC, yielding peptide 7 as colorless solid. RP-HPLC semi-preparative (38 - 55% in 20 min): t _R = 10.5 min. RP-HPLC (10 - 90% in 15 min): t _R = 8.64 min.

ESI-MS: aw _? (CgsHiarFlNbOs^Si): 2200.9; rrw: m/z = 735.2 [M+3H] ³⁺ , 1101.9 [M+2H] ²⁺ , 1468.4 [2M+3H] ³⁺ .

Synthesis of 9 (reference ligand) applying HOBt (1.2 eq.), TBTU (1.2 eq.) and DIPEA (3.6 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 9 as colorless solid.

RP-HPLC semi-preparative (38 - 55% in 20 min): t _R = 11.0 min.

RP-HPLC (10 - 90% in 15 min): t _R = 8.89 min.

ESI-MS: m _exaci (CgsHiasFNaoOggSgSi): 2128.9; m found, m/z = 711.3 [M+3H] ³⁺ , 1065.7 [M+2H] ²⁺ , 1420.7 [2M+3H] ³⁺ . Synthesis of 18 (reference ligand)

(1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). After Dde- deprotection, SiFA-BA (1.5 eq.) is conjugated applying HOAt (1.5 eq.), TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.) and the N- terminus is Fmoc-deprotected. R-DOTAGA(fBu) ₄ is conjugated applying HOAt (1.5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). The resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H ₂ 0, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvents are removed under reduced pressure. The precipitate is dissolved in fBuOH/H ₂ 0, frozen at -80 °C and final lyophilisation yields peptide 18 as colorless solid.

RP-HPLC semi-preparative (30 - 50% in 20 min): t _R = 16.1 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.2 min.

ESI-MS: m exact (C100H147FN22O27S2S1): 2199.0; m _fc w m/z = 550.7 [M+4H] ⁴⁺ , 733.8 [M+3H] ³⁺ , 1099.9 [M+2H] ²⁺ , 1466.1 [2M+3H] ³⁺ ,

3.4.3 Ligand Synthesis: positive Charge through additional Dap at SiFA

Synthesis of 23

The synthesis of the

(1.5 eq.) and 2,4,6-collidine (5.5 eq.). After Dde-deprotection, DOTA(fBu) ₃ (1.5 eq.) is conjugated, applying HOAt (1.5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). The A/-terminus is Fmoc-deprotected and conjugated with Fmoc-D-Dap(Boc)-OH (1.5 eq.) applying HOAt (1.5 eq.), TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.), followed by Fmoc-deprotection. SiFA-BA (1.5 eq.) is conjugated applying HOAt (1.5 eq.), TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). The resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H2O, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvents are removed under reduced pressure. The precipitate is dissolved in ffiuOH/H ₂ 0, frozen at -80 °C and final lyophilisation yields peptide 23 as colorless solid. RP-HPLC semi-preparative (37 - 45% in 20 min): t _R = 14.0 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12.2 min.

ESI-MS: mexaci (CiooHi44FN2i03iS ₂ Si): 2246.0; m foun _d, m/z = 749.6 [M+3H] ³⁺ , 1123.8 [M+2H] ²⁺ , 1499.0 [2M+3H] ³⁺ , 1685.7 [3M+4H] ⁴⁺ .

Synthesis of 19 tion and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 19 as colorless solid.

RP-HPLC semi-preparative (33 - 45% in 20 min): t _R = 17.6 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: m _exact (C98H139FN22O30S2S1): 2214.9; m w m/z = 739.7 [M+3H] ³⁺ , 1108.5 [M+2H] ²⁺ , 1477.8 [2M+3H] ³⁺ , 1662.5 [3M+4H] ⁴⁺ .

Synthesis of 39 HPLC, yielding peptide 39 as colorless solid.

RP-HPLC semi-preparative (34 - 44% in 20 min): t _R = 15.5 min. RP-HPLC (10 - 60% in 15 min): t _R = 12.3 min.

ESI-MS: m exact (CgeHiseFNziOzgSzSi): 2157.9; mw m/z = 720.6 [M+3H] ³⁺ , 1080.5 [M+2H] ²⁺ , 1440.9 [2M+3H] ³⁺ , 1620.3 [3M+4H] ⁴⁺ .

Synthesis of 40 cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 40 as colorless solid.

RP-HPLC semi-preparative (37 - 44% in 20 min): t _R = 14.8 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12,0 min.

ESI-MS: m exact (CiooH^FNzaOsiSzSi): 2271.9; nw: m/z = 758.7 [M+3H] ³⁺ , 1137.6 [M+2H] ²⁺ , 1517.2 [2M+3H] ³⁺ , 1706.5 [3M+4H] ⁴⁺ ,

Synthesis of 20

HOAt (1 .5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semipreparative RP-HPLC, yielding peptide 20 as colorless solid.

RP-HPLC semi-preparative (34 - 42% in 20 min): t _R = 17.1 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.7 min.

ESI-MS: m exact (C^H^FNzzOszSzSi): 2286,9; rrw m/z = 572.9 [M+4H] ⁴⁺ , 763.7 [M+3H] ³⁺ , 1144.5 [M+2H] ²⁺ . Synthesis of 41

HOAt (1.5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semipreparative RP-HPLC, yielding peptide 41 as colorless solid.

RP-HPLC semi-preparative (35 - 44% in 20 min): t _f? = 13.5 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.7 min.

ESI-MS: m exact (C101H145FN24O30S2S1): 2285.0; m w m/z = 763.1 [M+3H] ³⁺ , 1143.7 [M+2H] ²⁺ , 1525.4 [2M+3H] ³⁺ .

Synthesis of 42 deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 42 as colorless solid.

RP-HPLC semi-preparative (35 - 45% in 20 min): t _R = 14.6 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.8 min.

ESI-MS: rriexaci (C102H145FN24O32S2S1): 2329.0; mf _0U nd ^' · m/z - 778.0 [M+3H] ³⁺ , 1166.9 [M+2H] ²⁺ , 1555.6 [2M+3H] ³⁺ . Synthesis of 43 deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 43 as colorless solid.

RP-HPLC semi-preparative (35 - 45% in 20 min): t _R = 15.4 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: nw (C102H145FN24O32S2SO: 2329.0; rrw: m/z = 777.7 [M+3H] ³⁺ , 1165.8 [M+2H] ²⁺ , 1554.5 [2M+3H] ³⁺ .

Synthesis of 36 used as chelator, applying

HOAt (1.5 eq,), TBTU (1.5 eq.) and DIPEA (5.5 eq.) in DMF/NMP (1/1 v/v; 8 mL/g resin) for 3 h at room temperature. All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 36 as colorless solid.

RP-HPLC semi-preparative (34 - 43% in 20 min): t _R = 14.7 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.3 min.

ES!-MS: rriexaci (CgeHwFNbC^Si): 2212.0; nrw: m/z = 728.4 [M+3H] ³⁺ , 1106.7 [M+2H] ²⁺ , 1475.9 [2M+3H] ³⁺ . Synthesis of 37 HOAt (1 .5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 37 as colorless solid.

RP-HPLC semi-preparative (35 - 45% in 20 min): t R = 10.5 min.

RP-HPLC (10 - 60% in 15 min): t _R = 10.8 min.

ESI-MS: (C103H153FN24O28S2S1): 2285.1 ; m w m/z = 573.1 [M+4H] ⁴⁺ , 763.9 [M+3H] ³⁺ .

3.4.4 Ligand Synthesis: positive Charge through SiFAIin-Building Block

Synthesis of 24

(1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). After Dde-deprotection, DOTA(fBu)3 (1.5 eq.) is conjugated, applying HO At (1.5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). The A/-terminus is Fmoc-deprotected and conjugated with Me2-Gly-OH (3.0 eq.), applying HO At (3.0 eq.), TBTU (3.0 eq.) and 2,4,6-collidine (9.0 eq.) in DMF (8 mL/g resin) for 4 h at room temperature. The SiFA-moiety is formed, by incubation with SiFA-Br (3.0 eq.) and 2,4,6-collidine (6.0 eq.) in DOM (8 mL/g resin) for 24 h at room temperature. Reaction control via test cleavage (GP8; mild test cleavage) confirms correct but incomplete product formation. Nevertheless, the resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H2O, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvents are removed under reduced pressure. The precipitate is dissolved in fBuOH/H ₂ 0, frozen at -80 °C and final lyophilisation yields peptide 24 as colorless solid. Due to the quaternary amine present in the peptide, the formation of a TFA-salt is assumed.

RP-HPLC semi-preparative (37 - 53% in 20 min): t _R = 11.9 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12.2 min.

ESI-MS: m _exact (CggHuaFNziC^Sr): 2201.0; m w: m/z = 1101.0 [M+2H] ²⁺ , 1467.6 [2M+3H] ³⁺ , 1650.4 [3M+4H] ⁴⁺ .

Synthesis of 38 used as chelator, applying HOAt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (5.5 eq.) in DMF/NMP (1/1 vAr, 8 mL/g resin) for 3 h at room temperature. All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 38 as colorless solid.

RP-HPLC semi-preparative (35 - 43% in 20 min): t _R = 14.6 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.7 min.

ESI-MS: nw (C ₉₉ Hi ₄₆ FN ₂₄ 0 ₂₆ S ₂ Si ⁺ ): 2198.0; msw m/z = 734.5 [M+3H] ³⁺ , 1101.3 [M+2H] ²⁺ .

Synthesis of 48 transferable. After deprotection and cleavage from the resin, the crude product is purified applying semipreparative RP-HPLC, yielding peptide 48 as colorless solid.

RP-HPLC semi-preparative (40 - 48% in 20 min): t _R = 16.0 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: m _e x _act (CiosHugFNzsOsiSsSr): 2315.0; m found- m/z = 772.3 [M+3H] ³⁺ , 1032.7 [M-CH 2

C ₆ H ₄ -SifBu ₂ F+2H] ²⁺ , 1157.8 [M+2H] ²⁺ . Starting from precursor X19, the synthesis of ligand 49 is carried out analogously to the synthesis described for

24. All synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 49 as colorless solid.

RP-HPLC semi-preparative (40 - 45% in 20 min): t _R = 17.0 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.8 min.

ESI-MS: niexacf (C ₁₀ 5Hi52FN ₂ 4O32S ₂ Si ⁺ ): 2372.0; m found ^' , m/z = 791.3 [M+3H] ³⁺ , 1061.2 [M-CH ₂ - C ₆ H ₄ -SifBu ₂ F+2H] ²⁺ , 1186.4 [M+2H] ²⁺ .

Starting from precursor X15, the synthesis of ligand 50 is carried out analogously to the synthesis described for are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 50 as colorless solid.

RP-HPLC semi-preparative (42 - 47% in 20 min): t _R = 14.1 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: nw (CioiHi46FN ₂₂ 03oS ₂ Si ⁺ ): 2258.0; vnf _0U nd ^' · m/z = 753.3 [M+3H] ³⁺ , 1004.2 [M-CH ₂ - C ₆ H ₄ -SifBu ₂ F+2H] ²⁺ , 1129.4 [M+2H] ²⁺ . Starting from precursor X15, the synthesis of ligand 54 is carried out analogously to the synthesis described for 24. In contrast to the synthesis of 24, D03AM- acetic acid (1.8 eq.) is used as chelator, applying HOAt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (5.5 eq.) in DMF (8 mL/g resin) for 3 h at room temperature. All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 54 as colorless solid.

RP-HPLC semi-preparative (36 - 42% in 20 min): t _R = 11.8 min.

RP-HPLC (10 - 60% in 15 min): to = 11.6 min.

ESI-MS: vr\ exact (CioiHi ₄₉ FN ₂₅ 0 ₂₇ S ₂ Si ⁺ ): 2255.0; m _foun d, m/z = 564.8 [M+4H] ⁴⁺ , 752.7 [M+3H] ³⁺ , 1128.6 [M+2H] ²⁺ , 1504.8 [2M+3H] ³⁺ .

Starting from precursor X23, the synthesis of ligand 55 is carried out analogously to the synthesis described for 24. All synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 55 as colorless solid. RP-HPLC semi-preparative (34 - 45% in 20 min): t _R = 11.9 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.0 min.

ESi-MS: nw (Ci Hi FN O S ₂ Si ⁺ ): 2256.1 ; m _found : m/z = 565.1 [M+4H] ⁴⁺ , 753.2 [M+3H] ³⁺ , 1129.2 [M+2H] ²⁺ , 1505.1 [2M+3H] ³⁺ , 1693.8 [3M+4H] ⁴⁺ . Synthesis of 56 from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 56 as colorless solid. RP-HPLC semi-preparative (36 - 48% in 20 min): t _R = 12.6 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: m _exacf (CioiHueF^C^Sb): 2256.0; mw m/z = 753.0 [M+3H] ³⁺ , 1129.2 [M+2H] ²⁺ , 1505.3 [2M+3H] ³⁺ , 1694.0 [3M+4H] ⁴⁺ .

Synthesis of 57 steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 57 as colorless solid.

RP-HPLC semi-preparative (35 - 42% in 20 min): [ _R = 12.3 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.4 min.

ESI-MS: m _exacf (Ci Hi FN O _3i S ₂ Si ⁺ ): 2386.1 2256.0; p\ _ί0uhό · m/z = 597.7 [M+4H] ⁴⁺ , 796.4 [M+3H] ³⁺ , 1194.2 [M+2H] ²⁺ , 1592.3 [2M+3H] ³⁺ , 1791.3 [3M+4H] ⁴⁺ , 1910.7 [4M+5H] ⁵⁺ . Synthesis of 58 steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 58 as colorless solid.

RP-HPLC semi-preparative (38 - 42% in 20 min): t _R = 11.3 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: m _exacf (C ₁ 07H ₁ 57FN ₂ 5O32S ₂ Si ⁺ ): 2415.1; n\ _fou „ _d\ m/z = 806.1 [M+3H] ³⁺ , 1208.8 [M+2H] ²⁺ .

Synthesis of 59 cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 59 as colorless solid.

RP-HPLC semi-preparative (37 - 45% in 20 min): t _R = 14.1 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: rTw _i (Ci ₁₀ Hi54CIFN ₂₇ O32S ₂ Si ⁺ ): 2511.0; m _foun d m/z = 629.0 [M+4H] ⁴⁺ , 838.3 [M+3H] ³⁺ , 1257.0 [M+2H] ²⁺ , 1676.1 [2M+3H] ³⁺ , 1885.3 [3M+4H] ⁴⁺ . Synthesis of 61 used as chelator, applying

HOAt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (5.5 eq.) in DMF (8 mL/g resin) for 3 h at room temperature. All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 61 as colorless solid.

RP-HPLC semi-preparative (33 - 45% in 20 min): t« = 11.6 min.

RP-HPLC (10 - 60% in 15 min): t _R = 10.6 min.

ESI-MS: rrw, (Cio ₃ Hi ₅₉ FN ₂₇ 0 ₂₃ S ₂ Si ⁺ ): 2253.1 ; m w m/z = 564.5 [M+4H] ⁴⁺ , 752.2 [M+3H] ³⁺ , 1127.4 [M+2H] ²⁺ .

Synthesis of 44 TBTU (1.5 eq.) and 2,4,6- collidine (5.5 eq.). After Dde-deprotection, Me ₂ -Gly-OH (3.0 eq.) is conjugated, applying HOAt (3.0 eq.), TBTU (3.0 eq.) and 2,4,6-collidine (9.0 eq.) in DMF (8 mL/g resin) for 4 h at room temperature. The /V-terminus is Fmoc-deprotected and conjugated with DOTA(fBu)3 (1.5 eq), applying HOAt (1.5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). Subsequently the SiFA-moiety is formed, by incubation with SiFA-Br (3.0 eq.) and 2,4,6-collidine (6.0 eq.) in DCM (8 mL/g resin) for 24 h at room temperature. Reaction control via test cleavage (GP8; mild test cleavage) confirms correct but incomplete product formation. Nevertheless, the resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H2O, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvents are removed under reduced pressure. The precipitate is dissolved in fBuOH/H ₂ 0, frozen at -80 °C and final lyophilisation yields peptide 44 as colorless solid. Due to the quaternary amine present in the peptide, the formation of a TFA-salt is assumed.

RP-HPLC semi-preparative (35 - 45% in 20 min): t _R = 13.2 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: trt exact (CioiHi ₄₆ FN ₂₂ 0 ₃ oS ₂ Si ⁺ ): 2258.0; m _f ound m/z = 753.2 [M+3H] ³⁺ , 1129.2 [M+2H] ²⁺ , 1505.0 [2M+3H] ³⁺ .

Synthesis of 45 deprotection and cleavage from the resin, the crude product is purified applying semipreparative RP-HPLC, yielding peptide 45 as colorless solid.

RP-HPLC semi-preparative (32 - 42% in 20 min): i _R = 15.0 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.3 min.

ESI-MS: iriexacf (Cio ₇ Hi ₅₈ FN ₂₄ 0 _3i S ₂ Si ⁺ ): 2386.1 ; mw m/z = 597.4 [M+4H] ⁴⁺ , 795.8 [M+3H] ³⁺ , 1193.2 [M+2H] ²⁺ , 1590.7 [2M+3H] ³⁺ .

Synthesis of 46 deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 46 as colorless solid. RP-HPLC semi-preparative (35 - 42% in 20 min): t« = 12.1 min.

RP-HPLC (10 - 60% in 15 min): t* = 11.8 min.

ESI-MS: m _exaci (Ci07Hi57FN25O32S2Si ⁺ ): 2415.1 ; m found- m/z = 805.4 [M+3H] ³⁺ , 1207.7 [M+2H] ²⁺ , 1610.0 [2M+3H] ³⁺ .

Synthesis of 47 are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi- preparative RP-HPLC, yielding peptide 47 as colorless solid. RP-HPLC semi-preparative (40 - 50% in 20 min): t _/? = 15.5 min. RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: rrw (C ₁₀ 6H ₁₅₃ FN23O33S2Si ⁺ ): 2387.0; m found- m/z - 796.3 [M+3H] ³⁺ , 1068.7 [M-CH2- C ₆ H ₄ -SiiBu ₂ F+2H] ²⁺ , 1193.8 [M+2H] ²⁺ .

Synthesis of 51 Fmoc-D-Dap(Dde)-

OH (1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). After Dde- deprotection, DOTA(fBu)3 (1.5 eq.) is conjugated, applying HOAt (1.5 eq.), HATU (1.5 eq.) and DIPEA (4.5 eq.). The /V-terminus is Fmoc-deprotected and conjugated with Fmoc-D-Dap(Boc)- OH (1.5 eq.) applying HOAt (1.5 eq.) TBTU (1.5 eq.) and 2,4,6-collidine (5.5 eq.). After Fmoc- deprotection Me2-Gly-OH (3.0 eq.) is conjugated, applying HOAt (3.0 eq.), TBTU (3.0 eq.) and 2,4,6-collidine (9.0 eq.) in DMF (8 mL/g resin) for 4 h at room temperature. The SiFA-moiety is formed, by incubation with SiFA-Br (3.0 eq.) and 2,4,6-collidine (6.0 eq.) in DCM (8 mL/g resin) for 24 h at room temperature. Reaction control via test cleavage (GP8; mild test cleavage) confirms correct but incomplete product formation. Nevertheless, the resin bound peptide is deprotected and cleaved from the resin by treatment with TFA/TIPS/H2O, as described in GP7. The crude product is purified applying semi-preparative RP-HPLC and the solvents are removed under reduced pressure. The precipitate is dissolved in fBuOH/HaO, frozen at -80 °C and final lyophilisation yields peptide 51 as colorless solid. Due to the quaternary amine present in the peptide, the formation of a TFA-salt is assumed.

RP-HPLC semi-preparative (40 - 45% in 20 min): t _R = 14.5 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.6 min.

ESI-MS; nw (Cio4H ₁ 52FN2403iS ₂ Si ⁺ ): 2344.0; rrv _< w m/z = 781.3 [M+3H] ³⁺ , 1171.4 [M+2H] ²⁺ , 1156.9 [2M+3H] ³⁺ , 1757.1 [3M+4H] ⁴⁺ .

Synthesis of 60 Fmoc-Gly-OH is conjugated instead of Fmoc-D-Dap(Boc)-OH, applying applying HOAt (1.5 eq.), TBTU (1.5 eq.) and DIPEA (4.5 eq.). All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 60 as colorless solid.

RP-HPLC semi-preparative (37 - 43% in 20 min): t _R = 15.8 min.

RP-HPLC (10 - 60% in 15 min): t _R = 12.2 min.

ESI-MS: nw (CiosH^gFNzsOsiSgSr): 2315.0; m f _oun d, m/z = 579.8 [M+4H] ⁴⁺ , 772.8 [M+3H] ³⁺ , 1158.5 [M+2H] ²⁺ , 1544.9 [2M+3H] ³⁺ . Synthesis of 52 synthesis of 51,

Fmoc-Gly-OH is coupled before the conjugation of Me2-Gly-OH. All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semi-preparative RP-HPLC, yielding peptide 52 as colorless solid.

RP-HPLC semi-preparative (45 - 48% in 20 min): t _R = 11.3 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.7 min.

ESI-MS: m _exaci (Cio6Hi55FN25032S ₂ Si ⁺ ): 2401.1; mw m/z = 800.2 [M+3H] ³⁺ , 1199.9 [M+2H] ²⁺ , 1599.9 [2M+3H] ³⁺ , 1800.2 [3M+4H] ⁴⁺ .

Synthesis of 53

Starting from precursor X15, the synthesis of ligand 53 is carried out analogously to the synthesis described for 51. In contrast to the synthesis of 51, Fmoc-Gly-OH is coupled twice before the conjugation of Me ₂ -Gly-OH. All other synthesis steps are transferable. After deprotection and cleavage from the resin, the crude product is purified applying semipreparative RP-HPLC, yielding peptide 53 as colorless solid.

RP-HPLC semi-preparative (42 - 45% in 20 min): t _R = 13.5 min.

RP-HPLC (10 - 60% in 15 min): t _R = 11.8 min.

ESI-MS: vr\ exact (Cio ₈ Hi ₅₈ FN ₂₆ 0 ₃₃ S ₂ Si ⁺ ): 2458.1; mw: m/z = 819.2 [M+3H] ³⁺ , 1228.3 [M+2H] ²⁺ , 1637.4 [2M+3H] ³⁺ , 1841.8 [3M+4H] ⁴⁺ .

3.4.5 Metal Complexation for Biological Evaluation ^nat Ga ^m - , ^nat Lu ^m - and ^nat Pb ^M -chelate formation was achieved applying general procedures GP9, GP10 and GP11. The resulting analytical data (analytical RP-HPLC and ESI-MS) are listed below. ^nat Ga'"-Complexes

[ ^nat Ga]1

RP-HPLC (10 - 90% in 15 min): t _R = 10.9 min.

ESI-MS: m exact (CiooHiggFNigOsgSzSiGa): 2298.7; m found, m/z = 767.6 [M+3H] ³⁺ , 1150.7 [M+2Hp, 1533.9 [2M+3H] ³⁺ .

[ ^nat Ga]2

RP-HPLC (10 - 90% in 15 min): t _R = 10.4 min.

ESI-MS: nw (CiooHisgFNigOggSgSiGa): 2298.7; m _found - m/z = 767.6 [M+3H] ³⁺ , 1150.7 [M+2H] ²⁺ , 1533.9 [2M+3H] ³⁺ .

[ ^nat Ga]3

RP-HPLC (10 - 90% in 15 min): t _R = 11.1 min.

ESI-MS: nw; (CgjHissFNhgOsoSgSiGa): 2226.7; mw m/z = 743.3 [M+3H] ³⁺ , 1114.6 [M+2H] ²⁺ , 1485.9 [2M+3H] ³⁺ .

[ ^nat Ga]4

RP-HPLC (10 - 90% in 15 min): t _R = 11.4 min.

ESI-MS: rr\ _exact (Cg _/ H^sFNigOgoSgSiGa): 2226.7; mw m/z = 743.3 [M+3H] ³⁺ , 1114.6 [M+2H] ²⁺ , 1485.9 [2M+3H] ³⁺ .

[ ^nat Ga]5

RP-HPLC (10 - 90% in 15 min): t _R = 8.87 min.

ESI-MS: rrw (CiogHusFNgiOgeSgSiGa): 2504.7; mw m/z = 836.2 [M+3H] ³⁺ , 1253.5 [M+2H] ²⁺ , 1671.4 [2M+3H] ³⁺ .

[ ^na, Ga]6

RP-HPLC (10 - 90% in 15 min); t _R = 8.81 min.

ESI-MS: m _exacf (CggHmFNzoOsiSgSiGa): 2267.6; m f _oun d- m/z = 1135.6 [M+2H] ²⁺ , 1513.6 [2M+3H] ³⁺ .

[ ^nat Ga]7

RP-HPLC (10 - 90% in 15 min): t _R = 8.77 min.

ESI-MS: vn _exact (CgeH^FNgoOs^SiGa): 2267.66; m w m/z = 1135.6 [M+2H] ²⁺ , 1513.6 [2M+3H] ³⁺ .

[ ^na, Ga]8

RP-HPLC (10 - 90% in 15 min): t _R = 8.80 min. ESl-MS: vn exact (C ₉₅ Hi ₃ oFN ₂ o0 ₂₉ S ₂ SiGa): 2195.6; m found ^" · m/z - 1099.6 [M+2H] ²⁺ , 1466.4 [2M+3H] ³⁺ .

[ ^nat Ga]9

RP-HPLC (10 - 90% in 15 min): t _R = 8.81 min.

ESl-MS: mexac, (C ₉₅ Hi ₃ oFN ₂ o0 ₂₉ S ₂ SiGa): 2195.6; m found, m/z = 1099.6 [M+2H] ²⁺ , 1466.4 [2M+3H] ³⁺ .

[ ^nat Ga]18

RP-HPLC (10 - 60% in 15 min): t _R = 11.6 min.

ESl-MS: mexac (CiooHi ₄₅ FGaN ₂₂ 0 ₂₇ S ₂ Si): 2265.9; m _tad : m/z = 1134.6 [M+2H] ²⁺ , 757.0 [M+3H] ³⁺ .

[ ^nat Ga]19

RP-HPLC (10 - 60% in 15 min): t _R = 11.7 min.

ESl-MS: m exact (CgsHissFGaNzzC^oSzSi): 2282.8; m _/b ^: m/z = 1142.1 [M+2H] ²⁺ , 1522.5 [2M+3H] ³⁺ , 1712.1 [3M+4H] ⁴⁺ .

[ ^nat Ga]20

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESl-MS: m exact (Ci _0i Hi iFGaN O S ₂ Si): 2353.9; m found- m/z = 1178.2 [M+2H] ²⁺ , 1570.5 [2M+3H] ³⁺ , 1766.4 [3M+4H] ⁴⁺ .

[ ^nat Ga]23

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESl-MS: m ex act (CiooH^FGaNziOsiSzSi): 2312.9; mw m/z = 771.9 [M+3H] ³⁺ , 1157.6 [M+2H] ²⁺ , 1542.9 [2M+3H] ³⁺ .

[ ^nat Ga]24

RP-HPLC (10 - 60% in 15 min): t _R = 12.4 min.

ESl-MS: m exact (CggH^FGa^iOzgSgSF): 2267.9; m _fc w m/z = 756.6 [M+3H] ³⁺ , 1134.4 [M+2H] ²⁺ , 1512.6 [2M+3H] ³⁺ .

[ ^nat Ga]37

RP-HPLC (10 - 60% in 15 min): t _R = 11.1 min.

ESl-MS: m exact (CiosHisiFGa^OzsSgSi): 2352.0; mw m/z = 589.2 [M+4H] ⁴⁺ , 785.4 [M+3H] ³⁺ , 1177.6 [M+2H] ²⁺ .

[ ^nat Ga]39

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESl-MS: m _exacf (C ₉₆ Hi ₃₄ FGaN _2i 0 _2g S ₂ Si): 2224.8; m found, m/z = 743.0 1114.1.

[ ^nat Ga]40

RP-HPLC (10 - 60% in 15 min): t _R = 11.8 min.

ESl-MS: m _exacf (C^oHuoFGaNzsOsiSzSi): 2338.9; m^n* m/z = 781.1 [M+3H] ³⁺ , 1171.1 [M+2H] ²⁺ , 1561.3 [2M+3H] ³⁺ .

[ ^nat Ga]41

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: m _exact (CioiHi ₄₃ FGaN ₂₄ 0 ₃ oS ₂ Si): 2351.9; m _found, m/z = 785.2 [M+3H] ³ \ 1177.7 [M+2H] ²⁺ , 1571.0 [2M+3H] ³⁺ .

[ ^nat Ga]42

RP-HPLC (10 - 60% in 15 min): t _R = 11.7 min.

ESI-MS: nw (C^H _M sFGaN^SsSi): 2395.9; m _fou „ _d : m/z = 800.2 [M+3H] ³⁺ , 1200.3 [M+2H] ²⁺ , 1599.2 [2M+3H] ³⁺ .

[ ^nat Ga]43

RP-HPLC (10 - 60% in 15 min): t _R = min.

ESI-MS: nwi (Cio ₂ Hi ₄₃ FGaN ₂₄ 0 ₃₂ S ₂ Si): 2395.9; mw m/z = 799.8 [M+3H] ³⁺ , 1199.5 [M+2H] ²⁺ , 1599.8 [2M+3H] ³⁺ .

[ ^nat Ga]44

RP-HPLC (10 - 60% in 15 min): t _R = 12.1 min.

ESI-MS: nw (CioiHi44FGaN ₂₂ 03oS ₂ Si ⁺ ): 2324.9; m w m/z = 775.4 [M+3H] ³⁺ , 1162.4 [M+2H] ²⁺ , 1549.6 [2M+3H] ³⁺ .

[ ^nat Ga]45

RP-HPLC (10 - 60% in 15 min): t _R = 11.4 min.

ESI-MS: m _exact (Cio _/ H^FGaN^O^Sr): 2453.0; m w m/z = 817.9 [M+3H] ³⁺ , 1226.0 [M+2H] ²⁺ , 1634.6 [2M+3H] ³⁺ . 82.0; nw: m/z = 827.6 [M+3H] ³⁺ , 1240.8 [M+2H] ²⁺ , 1653.3 [2M+3H] ³⁺ .

[ ^nat Ga]47

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: nw (Cio ₆ Hi _5i FGaN ₂₃ 0 ₃₃ S ₂ Si ⁺ ): 2453.9; m w m/z = 817.9 [M+3H] ³⁺ , 1226.6 [M+2H] ²⁺ , 1635.3 [2M+3H] ³⁺ .

[ ^nat Ga]48

RP-HPLC (10 - 60% in 15 min): t _R = 12.1 min.

ESI-MS: m _exact (CiosHwFGaNssO^Sr): 2381.9; m f _ound, m/z = 794.1 [M+3H] ³⁺ , 1190.3 [M+2H] ²⁺ , 1587.6 [2M+3H] ³⁺ .

[ ^nat Ga]49

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: vn _exact (CiosHisoFGa^O^SF): 2438.9; m _found : m/z = 813.1 [M+3H] ³⁺ , 1218.8 [M+2Hp, 1625.1 [2M+3H] ³⁺ , 1829.4 [3M+4H] ⁴⁺ .

[ ^nat Ga]50

RP-HPLC (10 - 60% in 15 min): t _R = 12.2 min.

ESI-MS: mexaci (CioiHi44FGaN2203oS ₂ Si ⁺ ): 2324.9; m _fou „d m/z = 775.1 [M+3H] ³⁺ , 1162.1 [M+2H] ²⁺ , 1549.1 [2M+3H] ³⁺ , 1742.3 [3M+4H] ⁴⁺ .

[ ^nat Ga]51

RP-HPLC (10 - 60% in 15 min): t _R = 11.4 min.

ESI-MS: iri _exacf (Cio4H-i5oFGaN2403iS ₂ Si ⁺ ): 2410.9; m found: m/z = 803.5 [M+3H] ³⁺ , 1204.6 [M+2H] ²⁺ , 1605.6 [2M+3H] ³⁺ .

[ ^nat Ga]52

RP-HPLC (10 - 60% in 15 min): t _R = 11.5 min.

ESI-MS: rrw _f (CmHissFGaNzsC^Sr): 2468.0; mound, m/z = 822.3 [M+3H] ³⁺ , 1232.8 [M+2Hp, 1643.7 [2M+3H] ³⁺ .

[ ^nat Ga]53

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: m _exaci (CioeHiseFGalsfeeOasSaSr): 2525.0; m _f0U nd m/z = 841.4 [M+3Hp, 1261.3 [M+2Hp, 1680.8 [2M+3H] ³⁺ .

[ ^nat Ga]55

RP-HPLC (10 - 60% in 15 min): t _R = 11.1 min.

ESI-MS: m exact (Cio ₃ Hi54FGaN ₂₄ 0 ₂₆ S ₂ Si ⁺ ): 2323.0; m found m/z = 581.8 [M+4H] ⁴⁺ , 775.3 [M+3H] ³⁺ , 1163.2 [M+2Hp.

[ ^nat Ga]56

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: mexa _ci (CioiHi46FGaN ₂₄ 0 ₂₈ S ₂ Si ⁺ ): 2322.9; m found: m/z = 775.3 [M+3H] ³⁺ , 1161.9 [M+2H] ²⁺ , 1549.4 [2M+3Hp.

[ ^nat Ga]57

RP-HPLC (10 - 60% in 15 min): t _R = 11.4 min.

ESI-MS: iri _exaci (Ci07Hi56FGaN24O3iS ₂ Si ⁺ ): 2453.0; m found: m/z = 818.8 [M+3Hp, 1227.9 [M+2H] ²⁺ .

[ ^nat Ga]58

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: m _exaci (Cio/HissFGalshsC^SaSr): 2482.0; m _f0U nd m/z = 828.2 [M+3Hp, 1242.2 [M+2Hp, 1655.7 [2M+3Hp.

[ ^na *Ga]59

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: mexaci (CnoHisaCIFGalSbO^Sr): 2577.9; m _found : m/z = 860.6 [M+3Hp, 1290.4 [M+2Hp, 1720.9 [2M+3H] ³⁺ , 1935.3 [3M+4H] ⁴⁺ .

[ ^nat Ga]60

RP-HPLC (10 - 60% in 15 min): t _R = 12.2 min.

ESI-MS: m _exacf (C ₁₀ 3Hi47FGaN23O3iS ₂ Si ⁺ ): 2381.9; m _f< w m/z = 795.0 [M+3H] ³⁺ , 1192.0

[M+2H] ²⁺ , 1588.6 [2M+3H] ³⁺ . ^nat Lu'"-Complexes

[ ^nat Lu]19

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: nW _f (C ₉₈ Hi ₃₆ FLuN ₂₂ 0 ₃ oS ₂ Si): 2386.8; m found- m/z = 796.9 [M+3H] ³⁺ , 1194.6 [M+2H] ²⁺ , 1593.2 [2M+3H] ³⁺ .

[ ^na, Lu]20

RP-HPLC (10 - 60% in 15 min): t _R = 12.3 min.

ESI-MS: m _exacf (CioiHi4oFLuN2 ₂ 03 ₂ S ₂ Si): 2458.9; m _found ·. m/z = 820.8 [M+3H] ³⁺ , 1230.9 [M+2H] ²⁺ , 1641.4 [2M+3H] ³⁺ .

[ ^na, Lu]24

RP-HPLC (10 - 60% in 15 min): t _R = 12.4 min.

ESI-MS: m _exacf (CggHuoFLuNziOzgSzSF): 2372.9; m w m/z = 790.7 [M+3H] ³⁺ , 1185.8 [M+2H] ²⁺ , 1581.2 [2M+3H] ³⁺ .

[ ^nat Lu]44

RP-HPLC (10 - 60% in 15 min): t _R = 12.2 min.

ESI-MS: m _exacf (Ci ₀₁ Hi ₄₃ FLuN ₂₂ 0 ₃ oS ₂ Si ⁺ ): 2429.9; mw m/z = 809.9 [M+3H] ³⁺ , 1214.2 [M+2H] ²⁺ , 1618.7 [2M+3H] ³⁺ .

[ ^na, Lu]45

RP-HPLC (10 - 60% in 15 min): t _R = 11.6 min.

ESI-MS: m _exacf (Cio _/ HissFLu^OsiSgSr): 2558.0; m found- m/z = 852.6 [M+3H] ³⁺ , 1278.3 [M+2H] ²⁺ , 1703.4 [2M+3H] ³⁺ .

[ ^na, Lu]46

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: m _exacf (Cio _/ H^FLuNzsC^SzSr): 2587.0; mw m/z = 862.2 [M+3H] ³⁺ , 1292.8 [M+2H] ²⁺ , 1722.8 [2M+3H] ³⁺ .

[ ^nat Lu]47

RP-HPLC (10 - 60% in 15 min): t _R = 12.1 min.

ESI-MS: m _exacf (Cio6H ₁₅ oFLuN ₂ 3033S2Si ⁺ ): 2558.9; m _fotwlci : m/z = 853.0 [M+3H] ³⁺ , 1278.7 [M+2H] ²⁺ , 1704.1 [2M+3H] ³⁺ .

[ ^na, Lu]48

RP-HPLC (10 - 60% in 15 min): t _R = 12.1 min.

ESI-MS: m _exacf (CioaH^FLuNssOsiSzSi ^* ): 2486.9; m _found ·. m/z = 829.0 [M+3H] ³⁺ , 1242.7 [M+2Hp, 1656.3 [2M+3H] ³⁺ .

[ ^na *Lu]49

RP-HPLC (10 - 60% in 15 min): t _R = 12.0 min.

ESI-MS: nwi (CiosHugFLul^OsgSaSr): 2543.9; m found ^, m/z = 847.9 [M+3H] ³⁺ , 1271.2 [M+2Hp, 1694.7 [2M+3H] ³⁺ , 1907.3 [3M+4Hp.

[ ^nat Lu]50

RP-HPLC (10 - 60% in 15 min): t _R = 12.3 min.

ESI-MS: nwi (CioiHuaFLuNzgOsoSgSr): 2429.9; rrw: m/z = 810.0 [M+3Hp, 1214.0 [M+2Hp, 1618.3 [2M+3Hp.

[ ^nat Lu]51

RP-HPLC (10 - 60% in 15 min): U = 11.9 min.

ESI-MS: m _exacf (Cio ₄ Hi _4g FLuN ₂₄ 0 _3i S ₂ Si ⁺ ): 2515.9; m found- m/z = 838.4 [M+3Hp, 1257.5 [M+2H] ²⁺ , 1676.2 [2M+3Hp.

[ ^nat Lu]52

RP-HPLC (10 - 60% in 15 min): t _R = 11.9 min.

ESI-MS: m _exacf (CioeH^FLu^sC^SF): 2573.0; mw m/z = 857.3 [M+3Hp, 1285.0 [M+2Hp, 1714.6 [2M+3Hp.

[ ^nat Lu]53

RP-HPLC (10 - 60% in 15 min): t _R = 12.3 min.

ESI-MS: m _exacf (CmHissFLuNgeChsSgSr): 2630.0; mw m/z = 876.4 [M+3Hp, 1314.2 [M+2Hp, 1751.9 [2M+3Hp. ^nat Pb"-Complexes

[ ^nat Pb]36

RP-HPLC (10 - 60% in 15 min): t _R = 11.4 min.

ESI-MS: m _exacf (C ₉₈ H ₁₄ oFN ₂₅ 0 ₂₇ PbS ₂ Si): 2417.9; m found, m/z = 807.2 [M+3Hp, 1210.8 [M+2Hp, 1613.5 [2M+3Hp.

[ ^nat Pb]38

RP-HPLC (10 - 60% in 15 min): t _R = 11.8 min.

ESI-MS: m _exacf (CggHmF^OgePbSgSr): 2404.0; m _f0U nd: m/z = 801.7 [M+3Hp, 1202.0 [M+2Hp, 1603.4 [2M+3H] ³⁺ .

[ ^nat Pb]54

RP-HPLC (10 - 60% in 15 min): t _R = 11.6 min.

ESI-MS: m _exacf (CioiHwF^sOgyPbSgSr): 2461.0; m found, m/z = 616.2 [M+4H] ^4' , 821.2 [M+3Hp, 1231.5 [M+2Hp, 1641.7 [2M+3Hp.

[ ^nat Pb]61 RP-HPLC (10 - 60% in 15 min): t* = 10.6 min.

ESI-MS: rrw, (CiosHis _T FNzrOzaPbSsSr): 2459.1 ; mw m/z = 615.7 [M+4H] ⁴⁺ , 820.7 [M+3H] ³⁺ , 1230.5 [M+2H] ²⁺ .

4. Radiolabeling 4,1 ⁶⁸ Ga-Labeling

⁶⁸ Ga-labeling was done using an automated system (GallElut ⁺ by Scintomics, Germany) as described previously [28], Briefly, the ⁶⁸ Ge/ ⁶⁸ Ga-generator with SnC>2 matrix (IThemba LABS) was eluted with 1.0 M aqueous HCI, from which a fraction (1.25 mL) of approximately 80% of the activity (500-700 MBq), was transferred into a reaction vial (ALLTECH, 5 mL). The reactor was loaded before elution with 2-5 nmol of respective chelator conjugate in an aqueous 2.7 M HEPES solution (900 pL). After elution the vial was heated for 5 minutes at 95 °C. Purification was done by passing the reaction mixture over a solid phase extraction cartridge (C 8 light, SepPak), which was purged with water (10 mL) and the product eluted with 50% aqueous ethanol (2 mL), phosphate buffered saline (PBS, 1 mL) and again water (1 mL). After removing ethanol in vacuo, purity of the radiolabelled compounds was determined by radio-TLC (ITLC- SG chromatography paper, mobile phase: 0.1 M trisodium citrate and 1 :1 mixture ( v/v ) of 1 M ammonium acetate and methanol).

4.2 ¹⁸ F-Labeling

For ¹⁸ F-labeling a previously published procedure was applied [29],

4.3 ¹²⁵ I-Labeling of TOC

The reference ligand for in vitro studies [ ¹²⁵ l]TOC was prepared according to a previously published procedure [30], Briefly, 50-150 pg of the uniodinated precursor TOC were dissolved in 20 pL DMSO and 280 pL TRIS iodination buffer (25 mM TRIS-HCI, 0.4 mM NaCI, pH = 7.5). After addition of 5.00 pL (15 - 20 MBq) [ ¹²⁵ l]Nal (74 TBq/mmol, 3.1 GBq/mL, 40 mM NaOH, Hartmann Analytic, Braunschweig, Germany) the solution was transferred to a reaction vial, coated with 150 pg lodoGen®. The reaction was incubated for 15 min at RT and stopped by separation of the solution from the oxidant. The crude product of [ ¹²⁵ l]l-TOC was purified by RP-HPLC [(20% to 50% B in 15 min): fo = 9.4 min] and the final, dissolved product was treated with 10 Vol-% of a 100 mM solution of Na-ascorbate in H2O to prevent radiolysis.

5. In vitro Experiments 5.1 Determination of IC50

The SST ₂ -transfected CHO cells were cultivated in Dulbecco ^' s Modified Eagle Medium/Nutrient Mixture F-12 (DMEM/F-12) with Glutamax-I (1 :1) (Gibco), supplemented with 10% fetal calf serum (FCS) and maintained at 37 °C in a humidified 5% CO2 atmosphere. For determination of the half maximal inhibitory concentration (IC50), cells were harvested 24 ± 2 hours before the experiment, seeded in 24-well plates (1.0 * 10 ⁵ cells) and incubated in 1 mL/well of culture medium. After removal of the culture medium, the cells were treated once with 300 pL of HBSS-B (Hank’s balanced salt solution, Biochrom, Berlin, Germany, with addition of 1% bovine serum albumin (BSA)) and left with 200 pL HBSS-B. Next, 25 pL per well of solutions, containing either HBSS-B (control) or the respective ligand in increasing concentration (10 ^'1 ° - 10 ^~4 M in HBSS-B, were added with subsequent addition of 25 pL of [ ¹²⁵ l]TOC ([ ¹²⁵ l]Tyr ³ -Octreotide) (1.0 nM) in HBSS-B. Each concentration is investigated in triplicate. After 60 min incubation at room temperature, the experiment was terminated by removal of the assay medium and consecutive rinsing with 300 pL of cold PBS. The media of both steps were combined in one fraction and represent the amount of unbound radioligand. Afterwards, the cells were lysed with 300 pL of 1 M NaOH and united with the 300 pL 1 M NaOH of the following wash step. Quantification of bound and unbound radioligand was accomplished in a y-counter.

5.2 Internalization

The AR42J cells were cultivated in RPMI Medium (Gibco), supplemented with 10% fetal calf serum (FCS) and 2 mM L-GIU and maintained at 37 °C in a humidified 5% CO2 atmosphere. For internalization studies, AR42J cells were harvested 24 ± 2 hours before the experiment and seeded in 24-well PLL-plates (2 * 10 ⁵ cells in 1 mL/well). Subsequent to the removal of the culture medium, the cells were washed once with 300 pL RPMI (5% BSA, 2 mM L-GIU) and left to equilibrate for at least 15 min at 37 °C in 200 pL RPMI (5% BSA, 2 mM L-GIU). Each well was treated with either 25 pL of either RPMI (5% BSA, 2 mM L-GIU) or a 10 pM TOC solution (1 pM assay concentration) for blockade. Next, 25 pL of a solution, containing the ¹⁸ F-labeled SST ligand in a 20 nM concentration and also containing the reference ligand [ ¹²⁵ l]TOC in a 1 nM concentration, was added and the cells incubated at 37 °C for 15, 30 and 60 min. For each investigated time point a separate well plate is prepared. The experiment was terminated by placing the 24-well plate on ice and consecutive removal of the medium. Each well was rinsed with 300 pL RPMI (2 mM L-GIU) and the fractions from these first two steps combined, representing the amount of free radioligand. Removal of surface bound activity was accomplished by incubation of the cells with 300 pL of ice-cold acid wash solution for 15 min and rinsed again with another 300 pL of ice-cold acid wash. The internalized activity was determined by incubation of the cells in 300 pL 1 M NaOH and the combination with the fraction of a subsequent wash step with 300 pL 1.0 M NaOH. Each experiment (control and blockade) was performed in triplicate. Free, surface bound and internalized activity was quantified in a y- counter. Data were corrected for non-specific internalization and normalized to the specific- internalization observed for the radioiodinated reference compound.

5,3 Octanol-water Distribution Coefficient

Approximately 1 MBq of the labeled tracer was dissolved in 1 ml_ of a 1 : 1 mixture (by volumes) of phosphate buffered saline (PBS, pH 7,4) and n-octanol in an Eppendorf tube. After vigorous mixing of the suspension for 3 minutes at room temperature, the vial was centrifuged at 15000 g for 5 minutes (Biofuge 15, Heraus Sepatech, Osterode, Germany) and 100 pL aliquots of both layers were measured in a gamma counter. The experiment was repeated at least six times.

5.4 HSA Binding

RIAC Method

A gel filtration column Superdex 75 Increase 10/300 GL (GE Healthcare, Uppsala, Sweden) was beforehand calibrated following the producer’s recommendations with a commercially available gel filtration calibration kit (GE Healthcare, Buckinghamshire, UK) comprising conalbumin (MW: 75 kDa), ovalbumin (44 kDa), carbonic anhydrase (29 kDa), ribonuclease A (13.7 kDa) and aprotinin (6.5 kDa) as reference proteins of known molecular weight. AMSEC experiments were conducted using a constant flow rate of 0.8 mL/min at rt. A solution of HSA in PBS at physiological concentration (700 mM) was used as the mobile phase. SST2 ligands were labelled as described with molar activities of 10-20 GBq/pmol. Probes of 1.0 MBq of the radioligand were injected directly from the labelling solution. HSA binding was expressed as an apparent molecular weight MW calculated from the retention time of the radioligand using the determined calibration curve. Figure 1 shows the calibration plot of a Superdex 75 Increase gel filtration column using a low molecular weight gel filtration calibration kit in line with the data in the table below. MW: molecular weight. t _R : experimentally determined retention time. V: elution volume. K _aV : partition

For evaluation, experimentally determined retention times t R are first converted into elution volumes V _e by multiplying with the flow rate and thereafter converted into partition coefficients K _av following the equation where Vo is the column void volume (8.027 mL) and V _c is the geometric column volume (24 mL). Using the equation given by the trend line plot of the column calibration the apparent molecular weight MW is calculated as

6. In vivo Experiments

6.1 Mouse Model and Tumor Model

All animal experiments were conducted in accordance with general animal welfare regulations in Germany and the institutional guidelines for the care and use of animals. To establish tumor xenografts, AR42J cells (5 ^c 10 ⁶ cells / 100 pL) were suspended in Dulbecco modified Eagle medium / Nutrition Mixture F-12 with Glutamax-I (1 :1 ) and inoculated subcutaneously onto the right shoulder of 8 weeks old, female CD1 nu/nu mice (Charles River, Sulzfeld, Germany). Mice were used for experiments when tumors had grown to a diameter of 5-9 mm (7-15 days after inoculation).

6.2 mRET/CT Imaging

Imaging experiments were conducted using a MILabs VECTor ⁴ small-animal SPECT/PET/OI/CT. The resulting data were analyzed by the associated PMOD (version 4.0) software. Mice were anaesthetized with isoflurane and the ¹⁸ F-labeled compounds were injected via the tail vein (0.05 - 0.25 nmol; 1 - 20 MBq). Mice were euthanized 1 h p.i. and blood samples for later biodistribution studies were taken by cardiac puncture before image acquisition. Static images were acquired with 45 min acquisition time using the HE-UHR-M collimator and a step-wise spiral bed movement. All images were reconstructed using the MILabs-Rec software (version 10.02) and a pixel-based Similiarity-Regulated Ordered Subsets Expectation Maximization (SROSEM) algorithm, with a window-based scatter correction (20% below and 20% above the photopeak, respectively). Voxel size CT: 80 pm, 1.6 mm Gaussian blurring, with calibration factor in kBq/mL and decay correction. For blockade 20 pg of TOC was administered directly before tracer injection.

6.3 Biodistribution

Approximately 0.5-2.0 MBq (0.05 - 0.25 nmol) of the ¹⁸ F-labeled SST2-ligands were injected into the tail vein of AR42J tumor-bearing female CD1 nu/nu mice and sacrificed after 1 h post injection (n = 3-5). Selected organs were removed, weighted and measured in a y-counter.

II. Results

The Tables 1 , 2, and 3 summarize in vitro data of the herein described SST ligands.

The reference ligands in table 1 exemplify the difficulties regarding the implementation of the radiohybrid structure (combination of chelator and SiFA-moiety). The incorporated chelator counter balances the high lipophilicity of the SiFA-moiety (Ligands [Ga]1 to [Ga]9). But the usage of SiFA-benzoic acid and DOTA or DOTAGA connected directly via the amino acid D- Dap as a trivalent linker impacted the target affinity (IC ₅ o) negatively. Therefore, specific optimization steps had to be conducted, to develop ligands of sufficient target affinity, lipophilicity and a low affinity towards human serum albumine as defined in the claims and illustrated by the following examples.

The Tables 4, 5, and 6 summarize the results of the in vivo mouse experiments. For all biodistribution studies, female CD1 nu/nu mice with AR42J tumor xenografts, were used and sacrificed 1 h post injection.

The figures 2, 3 and 4 show the MIPs of the PET/CT scans of AR42J tumor bearing female mice (CD1 nu/nu). To perform the static PET/CT scan, mice were euthanized 1 h p.i. and images were acquired with 45 min acquisition time.

Figure 2 shows the PET/CT MIP of [18F][natGa]19 in female AR42 tumor-bearing CD1 nu/nu mice from 10-30%ID/mL. Arrows indicate organs/volumes of interest: solid = tumor, points = kidney

Figure 3 shows the PET/CT MIP of [18F][natGa]46 in female AR42 tumor-bearing CD1 nu/nu mice from 5-30%ID/mL Arrows indicate organs/volumes of interest: solid = tumor, points = overlap of kidneys and organs that express the receptor on a physiological level

(e.g. stomach and pancreas). Figure 4 shows the PET/CT MIP of [18F][natGa]50 in female AR42 tumor-bearing CD1 nu/nu mice from 5-40%ID/mL Arrows indicate organs/volumes of interest: solid = tumor, points = overlap of kidneys and organs that express the receptor on a physiological level

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