Introduction

The present invention relates to the use of iminosydnone compounds in processes for the preparation of conjugates of two compounds of interest. The invention further relates to the use of said iminosydnone compounds in a process for releasing a third compound of interest. The invention finally relates to said new iminosydnone compounds.

Background of the invention

The present invention relates to the domain of click chemistry (bioorthogonal reaction) and of bioconjugation of compounds of interest. Five main approaches are currently available for metal-free coupling two different compounds of interest ( · and ■ ). These approaches are presented on the scheme below. Among these approaches only Tetrazine/Cyclooctene reaction (approach 2) has a modification that allows simultaneous coupling of two entities and release of the third compound (Angew. Chem. Int. Ed. 2013, 52, 141 12-141 16). ction Approach 2: Tetrazine/Cyclooctene reaction

reaction

The inventors of the present application recently discovered that reaction of a sydnone and an alkyne could be efficiently used to perform efficient bioorthogonal reactions ( olodych et al. Angew. Chem. Int. Ed. 2013, 52, 12056-12060).

Bioconjugation reactions and cleavage reactions, for instance bioconjugation and cleavage reactions involving proteins, are often performed in highly dilute conditions, for instance because of the low available amount of the starting biomaterial, or because the solubility of said starting biomaterial is low in the coupling and or cleavage conditions. Furthermore, a high level of bioorthogonality of these reactions is mandatory for applications in the fields of chemical biology and drug release which deal with in vivo experiments.

Consequently, it is important in the domain of bioorthogonal reactions to use efficient coupling and cleavable reagents allowing high yields and fast coupling and cleavage kinetics even in the presence of the plethora of chemical functionalities present in biological media.

Such reactions are potentially of high interest in several areas; one of them is antibody-drug- conjugate (ADC) cleavage wherein an antibody, such as an anti-tumor antibody, and a drug, such as an anticancer drug, can be selectively released with a specific probe preferably administered in a second step.

The Applicant of the present invention evidenced that the use of iminosydnone derivatives affords a unique process allowing both the conjugation and the release of compounds of interest with high efficiency, kinetics and bioorthogonality. These iminosydnone compounds can be advantageously used for the conjugation and the release of compounds of interest.

Summary of the invention

A first object of the invention is a process for the preparation of a functionalized compound of interest C 1 of formula (II) :

comprising the step of contacting a compound of interest CI bearing a reactive group with an iminosydnone of formula (I):

wherein F is a functional group selected among specific groups which allow bonding to the reactive group of the compound of interest CI. Another object of the invention is a functionalized compound of interest CI of formula (II):

Another object of the invention is a conjugate of formula (IV): wherein CI and C2 are compounds of interest.

Another object of the invention is a process for the preparation of a conjugate of formula (IV):

comprising the step of contacting a compound of formula (II) with a compound of interest C2 bearing a reactive group which is able to react with R.

Another object of the invention is a process for the preparation of a conjugate of formula (V):

wherein C3 is a third compound of interest, comprising a step of contacting a compound of formula (VI):

with the compound of formula (II) or with the conjugate of formula (IV). Another object of the invention is a conjugate of formula (V):

I _Vi W /p, A further object of the invention is an iminosydnone of formula (Γ)

Brief description of the fi2ures

Figure 1 HPLC monitoring of the reaction between iminosydnone Im 5 and the cyclic alkyne TMTH.

Figure 2 HPLC monitoring (b) and linear regression curve (c) for the reaction of Im2 with

TMTH (a).

Figure 3 Linear regression curves for the reactions of iminosydnones Im6 and Im7 with

TMTH.

Detailed description of the invention A first object of the present invention is a process for the preparation of a functionalized compound of interest C 1 of formula (II)

wherein n is an integer and preferably ranges from 1 to 100, comprising the step of contacting a compound of interest CI selected from an antibody, a protein, a drug, a fluorophore, a group of atoms comprising at least one radioactive atom, a DNA fragment, a nanoparticle and a polymer, with an iminosydnone of formula (I):

wherein

CI bears a reactive group which is able to react with F,

X is selected from the group consisting of a hydrogen atom, a halogen atom, an aryl diazo group, an alkyl group, an aryl group, an alkenyl group, an alkynyl group, an alkoxy group, a thioether group and an amino group,

F is a functional group selected from the group consisting of: - a carboxylic acid COOH group,

- a thiol SH group,

- a maleimide group,

- an activated ester,

- a halogen atom,

- an alkene or alkyne group, optionally interrupted by at least one heteroatom selected among O, N and S,

- an amino (-NRR') group, wherein and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- a diazonium (-N ₂ ⁺ ) group, optionally in presence of a counterion,

- a boronic acid -B(OR")2 group, wherein R" is a hydrogen atom or an alkyl group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group,

- a -C≡C-C≡N group,

- an aldehyde CHO group,

- a ketone COR' " group, wherein R'" is an alkyl group, and

- an alkyl group substituted by at least one of said groups,

F' is a carbonyl group (C=0), a sulfonyl group (SO2) or a phosphoryl group (P=0),

R is selected from

an optionally substituted aryl group, an optionally substituted alkyl, alkenyl or alkynyl group, an optionally substituted alkoxy or aralkyloxy group, an optionally substituted thioether group, an optionally substituted amino group, wherein the alkyl, alkenyl and/or alkynyl groups may be interrupted by at least one heteroatom selected from nitrogen, oxygen and sulphur atoms and wherein said substituents are one or more groups selected from:

- a carboxylic acid COOH group,

- a thiol SH group,

- a maleimide group,

- an activated ester, - a halogen atom,

- an alkene or alkyne group, optionally interrupted by at least one heteroatom selected among O, N and S,

- an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- a diazonium (-N2 ⁺ ) group, optionally in presence of a counterion,

- a boronic acid -B(OR' ') ₂ group, wherein R" is a hydrogen atom or an alkyl group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group,

- a -C≡C-C≡N group,

- an aldehyde CHO group,

- a ketone COR' ' ' group, wherein R" ' is an alkyl group, or

a linker bearing at least one of the above substituents, and

Ar is an optionally substituted aromatic group.

In an embodiment, n is from 1 to 50, preferably from 1 to 30. In a specific embodiment, n is 1.

In the above definitions of F and R, the counterion can be any ion appropriate for compensating the charge of the diazonium group, and may be easily chosen by anyone of ordinary skill in the art. For instance, the couterion may be selected from the group consisting of halogenates, BF4, NO3-, HSO4-, PF<f CH3COO , N(S0 ₂ CF ₃ )2-, CF3SO3-, CH3SO3-, CF3COO , (CH ₃ 0)(H)P0 ₂ - and N(CN ^" .

In the context of this description, a halogen atom is a chlorine, iodine, bromine or fluorine atom. Preferably, a halogen atom is a bromine or a chlorine atom, in particular a bromine atom. An alkyl group is a linear saturated hydrocarbon group comprising from 1 to 20 carbon atoms, a branched saturated hydrocarbon group comprising from 3 to 20 carbon atoms or a cyclic saturated hydrocarbon group comprising from 4 to 20 carbon atoms. Preferably, the alkyl group according to the invention comprises from 1 to 10, in particular from 1 to 6, carbon atoms. Examples of alkyl groups comprise methyl, ethyl, propyl, isopropyl, butyl, tertbutyl, isobutyl, n-pentyl, n-hexyl and cyclohexyl groups. An alkenyl group (or an alkene) is a linear hydrocarbon group comprising from 2 to 20 carbon atoms, a branched hydrocarbon group comprising from 4 to 20 carbon atoms, or a cyclic hydrocarbon group comprising from 4 to 20 carbon atoms and comprising at least one C=C double bond. Preferably, the alkenyl group according to the invention comprises from 2 to 10, in particular from 2 to 6, carbon atoms. Examples of alkenyl groups comprise ethylenyl, propylenyl and cyclohexenyl groups.

An alkynyl group (or an alkyne) is a linear hydrocarbon group comprising from 2 to 20 carbon atoms, a branched hydrocarbon group comprising from 4 to 20 carbon atoms or a cyclic hydrocarbon group comprising from 4 to 20 carbon atoms and comprising at least one C≡C triple bond. Preferably, the alkynyl group according to the invention comprises from 2 to 10, in particular from 2 to 9, carbon atoms. Examples of alkynyl groups comprise ethynyl, propynyl, octynyl, cyclooctynyl and cyclononynyl groups.

In specific embodiments of the present invention, the alkyl, alkenyl and/or alkynyl groups may be interrupted by at least one heteroatom, preferably independently selected from nitrogen, oxygen and sulphur atoms.

An alkoxy group is an alkyl group, bonded to the rest of the molecule through an oxygen atom. An aralkyloxy group is an aralkyl group, such as a benzyl group, bonded to the rest of the molecule through an oxygen atom.

A thioether group is an alkyl group, bonded to the rest of the molecule through a sulfur atom. An aryl diazo group is a N2 group bonded to an aromatic group. A carboxyl group is a COOH group. A nitro group is a NO2 group.

An amino group is a NR1R2 group, wherein Ri and R2 are independently selected from the group consisting of hydrogen atoms, aromatic groups (such as a phenyl or tolyl group) and alkyl groups. In an embodiment, at least one of Ri and R2 is an alkyl group. Such an amino group is an alkylamino group. In an embodiment, Ri and R2 are both alkyl groups. Such an amino group is a dialkylamino group.

An "activated ester" is an ester with a good leaving group, such as a N-hydroxysuccinimide ester, a N-hydrophthalimide ester, a perfluorinated ester or an acylurea. An example of perfluorinated ester is the following:

According to the present invention, the optionally substituted aromatic group Ar is selected from the group consisting of:

a phenyl group;

a heteroaromatic group, such as pyridine, thiophene, imidazole, thiazole, pyrazole, pyrole or furane; and

a polyaromatic group, such as anthracene or phenanthrene.

The phenyl, heteroaromatic and/or polyaromatic group may be substituted with at least one substituent (in addition to the F group when the aromatic is substituted with a F group), preferably selected from the group consisting of a halogen atom, an alkyl group, an alkoxy group, a carboxyl COOH group, a COOR3 group, wherein R3 is an alkyl group, and a nitro NO2 group.

In an embodiment, the optionally substituted aromatic group is an optionally substituted phenyl group, preferably a non-substituted phenyl group.

The linker optionally comprised in may be any hydrocarbon chain comprising C and H atoms and optionally O and/or N and/or S atoms, such as a -(CH ₂ )q(CH20)r -COO-(CH2)q'(CH ₂ 0)r' group, a -(CH ₂ )q(CH20)r-NH-C(=0)-(CH2)q'(CH ₂ 0)r' group, a -(CH ₂ )q(CH ₂ 0)r-CONH- (CH2)q'(CH ₂ 0)r' group, wherein q and r are integers independently ranging from 0 to 10, or a triazolyl group, for instance.

In an embodiment, X is a halogen atom.

When Ar is an optionally substituted phenyl group, the functional group F is in meta or para position of the phenyl group, preferably in para position.

When Ar is an optionally substituted heteroaromatic or polyaromatic group, the functional group F can be in any position of the aromatic group.

In a preferred embodiment, the functional group F is selected from the group consisting of:

- a carboxylic acid COOH group,

- a thiol SH group,

- a maleimide group, - an activated ester,

- an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups as defined above,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group,

- a -C≡C-C≡N group, and

- an alkyl group substituted by at least one of the groups above.

In a highly preferred embodiment, the functional group F is selected from the group consisting of a carboxylic acid COOH group, an activated ester, such as a N-hydroxysuccinimide, a N- hydrophthalimide ester, a perfluorinated ester or an acylurea, and an alkyl group substituted by at least one of these groups.

In a preferred embodiment, F' is a C=0 group and R is an amino group. Preferably, the R amino group is bonded through the nitrogen atom to the C=0 F' group, thus forming a urea moiety. In another preferred embodiment, F' is a C=0 group and R is an alkoxy group such as an tert- butoxy group. Preferably, the R alkoxy group is bonded through the oxygen atom to the C=0 F' group, thus forming a carbamate moiety.

In a preferred embodiment, F' is a C=0 group, R is an amino or alkoxy group forming a urea or carbamate moiety respectively as disclosed above, and X is a halogen atom, preferably selected from bromine and chlorine atoms.

Examples of iminosydnones of formula (I) that may be used in the above process are selected from the group consisting of:

(2-(4-hydroxyphenyl)- 1 ,2,3-oxadiazol-2-ium-5-yl)(p-tolylcarbamoyl)amide ;

- (2-(4-carboxyphenyl)-l,2,3-oxadiazol-2-ium-5-yl)(p-tolylcarb amoyl)amide ; and

((4-(ethoxycarbonyl)phenyl)carbamoyl)(2-(4-hydroxyphenyl)- 1 ,2,3-oxadiazol-2-ium- 5-yl)amide.

In an embodiment, n is from 1 to 50, preferably from 1 to 30. In a specific embodiment, n is 1. The contacting step of the processes according to the invention may be performed by any technique known in the art, for instance by dissolution and/or dispersion of both compounds in a solvent. The contacting may be performed under stirring, for instance mechanical or magnetic stirring. The contacting may be performed at room temperature, ie at a temperature comprised between 18 and 25°C, or at low temperature, ie at a temperature inferior to 18°C, or even at high temperature, ie at a temperature higher than 25 °C, for instance comprised between 25 and

150°C.

The process of preparation of a functionalized compound according to the invention may comprise a preliminary step of covalent bonding of a reactive group to CI, in the case where C 1 does not bear a reactive group able to react with the functional group F of the iminosydnone compound. However, in a preferred embodiment, C I intrinsically bears such a reactive group. In an embodiment, the reactive group is selected from the group consisting of :

- a carboxylic acid COOH group,

- a thiol SH group,

- an activated ester

- a halogen atom,

- an alkene or alkyne group, optionally interrupted by at least one heteroatom selected among O, N and S,

- an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups as defined above,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- a diazonium (-N ₂ ⁺ ) group, optionally in presence of a counterion,

- a boronic acid -B(OR") ₂ group, wherein R" is a hydrogen atom or an alkyl group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group,

- a -C≡C-C≡N group,

- an aldehyde CHO group, - a ketone COR' ' ' group, wherein R" ' is an alkyl group.

In a preferred embodiment, the reactive group is selected from the group consisting

- a carboxylic acid COOH group,

- a thiol SH group,

- an activated ester,

- an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups as defined above,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group, and

- a -C≡C-C≡N group.

In a highly preferred embodiment, the reactive group is an amino group or a thiol group.

The racemic forms, tautomers, enantiomers, diastereoisomers, epimers, solvates and salts of the compounds used in the processes according to the invention are also part of the scope of the invention.

As examples of salts may be cited acid addition salts, such as hydrochloric, hydrobromic, hydroiodic, phosphoric, and the like. Representative examples of suitable organic acids include formic, acetic, trichloroacetic, trifluoroacetic, propionic, benzoic, cinnamic, citric, fumaric, maleic, methanesulfonic and the like. Further examples of pharmaceutically acceptable inorganic or organic acid addition salts include the pharmaceutically acceptable salts listed in J. Pharm. Sci. 1977, 66, 2, and in Handbook of Pharmaceutical Salts: Properties, Selection, and Use edited by P. Heinrich Stahl and Camille G. Wermuth 2002.

Another object of the invention is a functionalized compound of interest CI of formula (II): wherein CI, Ar, X, F', n and R are as defined above and CI and Ar are covalently linked by a functional group. This functional group results from the reaction between the reactive group of C 1 and the functional group F, such as an ester or amide function. Another object of the invention is a conjugate of formula (IV): wherein X, Ar, F' and CI are as described above, m is an integer which ranges from 1 to 100, C2 is a compound of interest selected from an antibody, a protein, a drug, a fluorophore, a group of atoms comprising at least one radioactive atom, a DNA fragment, a nanoparticle and a polymer C 1 and Ar are covalently linked by a functional group (resulting from the reaction between the reactive group of CI and the functional group F) and C2 and F' are covalently linked by a functional group. This functional group results from the reaction between the reactive group of C2 and R and may be for instance as an ester or amide function. In an embodiment, m is from 1 to 50, preferably from 1 to 30. In a specific embodiment, m is 1.

Another object of the invention is a process for the preparation of a conjugate of formula (IV) as described above, comprising the step of contacting a compound of formula (II) with a compound of interest C2 bearing a reactive group which is able to react with R. It is understood that, in this embodiment of the invention, R is itself a reactive group.

Specific examples of R for use in this embodiment are:

- a carboxylic acid COOH group,

- a thiol SH group,

- an activated ester

- an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups as defined above, and

- a -C≡C-C≡N group. The process of preparation of the above conjugate may comprise a preliminary step of covalent bonding of a reactive group to C2, in the case where C2 does not bear a reactive group able to react with the reactive group R of the iminosydnone compound. However, in a preferred embodiment, C2 intrinsically bears such a reactive group.

In an embodiment, this reactive group of C2 is selected from the group consisting of :

- a carboxylic acid COOH group,

- a thiol SH group,

- a maleimide group,

- an activated ester

- a halogen atom,

- an alkene or alkyne group, optionally interrupted by at least one heteroatom selected among O, N and S,

- an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups as defined above,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- a diazonium (-N ₂ ⁺ ) group, optionally in presence of a counterion,

- a boronic acid -B(OR")2 group, wherein R" is a hydrogen atom or an alkyl group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group,

- a -C≡C-C≡N group,

- an aldehyde CHO group,

- a ketone COR' ' ' group, wherein R" ' is an alkyl group.

In a preferred embodiment, the reactive group is selected from the group consisting of:

- a carboxylic acid COOH group,

- a thiol SH group,

- a maleimide group,

- an activated ester, - an amino (-NRR') group, wherein R and R' are independently hydrogen atoms, alkyl, alkene, alkyne or aryl groups as defined above,

- a hydroxylamine (-ONH2) group,

- a hydrazine (-NH-NH2) group,

- an azido (-N3) group,

- an isocyanate (-N=C=0) or isothiocyanate (-N=C=S) group,

- a chlorosulfonyl (-SO2CI) group, and

- a -C≡C-C≡N group. In a highly preferred embodiment, the reactive group is an amino group or a thiol group.

Another object of the invention is a process for the preparation of a conjugate of formula (V):

wherein p is an integer ranging from 1 to 100, CI, Ar and X are as defined above, CI is a first compound of interest, and C3 is a third compound of interest selected from an antibody, a protein, a drug, a fluorophore, a group of atoms comprising at least one radioactive atom, a DNA fragment, a nanoparticle and a polymer, comprising a step of contacting a compound of formula (VI):

with a compound of formula (II) or with a conjugate of formula (IV) according to the invention. In an embodiment, p is from 1 to 50, preferably from 1 to 30. In a specific embodiment, p is 1. In a preferred embodiment where the compound of formula (VI) is reacted with a conjugate of formula (IV), this process simultaneously allows the release of a derivative of C2 of formula

(VII):

The process for the preparation of a conjugate of formula (V) may comprise a preliminary step of covalent bonding of a strained alkyne moiety to the compound of interest C3.

By "strained alkyne", it is meant a cyclic alkyne, in particular cyclooctynes such as bicyclo- [6.1.0]-nonyne (BCN) or cycloheptynes such as tetramethylthiacycloheptyne (TMTH). In the case of BCN, for instance, the compound of interest C3 may be bonded to BCN by reacting a C3-0-CO-C1 compound with the hydroxy group of BCN, so as to form a carbamate bond. In the case of TMTH, the latter may be alkylated on its sulphur atom by reaction with a C3-CH2- Br compound.

Another object of the invention is a conjugate of formula (V):

wherein CI , Ar, X and C3 are as defined above. Another object of the invention is a process for releasing a derivative of C2 of formula (VII):

(VII) N-F-C2 ,

comprising a step of contacting a conjugate of formula (IV): as described above with a compound comprising a strained alkyne moiety, preferably a cyclic alkyne moiety, in particular a cyclooctyne moiety, for instance BCN (bicyclononyne). More preferably, the conjugate of formula (IV) is reacted with a compound of formula (VI) as described above.

Another object of the invention is an iminosydnone of formula (Γ):

wherein

X is a halogen atom,

F, F', R and Ar are as described above.

The iminosydnone compounds of formulas (I) and (Γ) can be used advantageously in order to couple both compounds of interest CI and C3 or CI and C2 and/or release the compound of interest C2, as explained above. In an embodiment, CI is a nanoparticle or an antibody, C2 is a drug and C3 is a fiuorophore or a group of atoms comprising at least one radioactive atom. In this embodiment, the iminosydnone of the invention affords the release of the drug, which may then enter its target cells, and the labeling of the nanoparticle or the antibody. In a particular embodiment, CI is an antibody and this embodiment leads to the release of a drug from a therapeutic antibody and at the same time the labeling of the antibody, therefore allowing theranostic applications. In an especially preferred embodiment of this invention, the drug is a chemotherapeutic drug and the labeling of the antibody allows imaging the tumor.

The iminosydnones of formulas (I) and (Γ) react very efficiently with strained alkynes, such as cyclic alkynes, in particular cyclooctynes. The coupling reaction implies the formation of a cycloadduct formed by a [3+2] cyclization turning to a stable pyrazole said cycloadduct by retro-Diels Alder reaction, triggering the release of a R-F'-NCO molecule, which in aqueous medium, for instance in water, may spontaneously evolve to R-F'-NH ₂ through hydrolysis and/or decarboxylation reactions. The reaction with a compound according to the invention with a cycloalkyne is represented as example on the scheme below.

The present compounds allow the efficiency of the reaction to be maintained in biological media, such as culture media, cell lysates or plasma.

These iminosydnones may be synthesized by any appropriate method known by one of ordinary skill in the art.

For instance, the scheme below presents different synthesis routes for iminosydnones of formulas (I) and (Γ). The Ar groups substituting the nitrogen atom of the iminosydnones may be substituted with a F group. In this scheme, the term NBS designates N-bromosuccinimide. Ar— NH ₂

BrCH ₂ CN

or

CH ₂ 0, KCN

-CN

Ar— NH tBuONO

The following examples are provided as illustrative, and not limitative, of the present invention.

Examples

Example 1: Synthesis of svdnones

In the following examples, the provided yields are molar yields unless specified differently.

ImO-1 (intermediate): 5-amino-3-(4-hydroxyphenyl)-l,2,3-oxadiazol-3-ium chloride

2

To a solution of 2-((4-hydroxyphenyl)amino)acetonitrile (2.56 g, 12 mmol) in tetrahydrofuran THF (60 mL) was added amyl nitrite (1.85 eq, 22.2 mmol). The mixture was stirred for 16h at room temperature (r.t.) and then HC1 (5 mL, 4M solution in dioxane) was added. The resulting mixture was stirred for 24 h at r.t. The precipitate was collected by filtration and washed with Et ₂ 0 and dried to yield pure product as a yellow solid (850 mg, 4.8 mmol, 40%). ¾ NMR (400 MHz, DMSO-de, δ ppm): 9.71 (s, 2 H), 8.48 (s, 1 H), 7.88 (d, / = 9.1 Hz, 2 H), 7.09 (d, J = 9.1 Hz, 2 H).

¹³ C NMR (100 MHz, DMSO-de, δ ppm): 169.1 , 162.1 , 124.1 , 124.0, 116.6, 101.0.

ImO-2 (intermediate): 5-amino-3-(4-carboxyphenyl)-l,2,3-oxadiazol-3-ium chloride

To a solution of 4-(( cyanomethyl)amino)benzoic acid (1.13 g, 6.42 mmol) in THF (60 mL) was added amyl nitrite (1.85 eq, 11.9 mmol). The mixture was stirred for 16h at r.t. and then HCl (5 mL, 4M solution in dioxane) was added. The resulting mixture was stirred for 24 h at r.t. The precipitate was collected by filtration and washed with Et20 and dried to yield pure product as a white solid (161 mg, 0.67 mmol, 10%).

¾ NMR (400 MHz, DMSO-de, δ ppm): 9.97 (br. s., 2 H), 8.73 (s, 1 H), 8.27 (d, / = 8.6 Hz,

2 H), 8.18 (d, / = 8.6 Hz, 2 H).

¹³ C NMR (100 MHz, DMSO-de, δ ppm): 169.4, 165.7, 135.5, 135.1 , 131.0, 123.1, 102.7.

Im 6 (comparative): (2-(4-hydroxyphenyl)-l,2,3-oxadiazol-2-ium-5-yl)(p- tolylcarbamoyl)amide

To a solution of p-tolyl isocyanate (47 mg, 0.351 mmol) and iminosydnone IniO-1 S (75 mg, 0.3 1 mmol) in THF (5 mL) was added a solution of NaHC03 (1 eq., 30 mg, 0.35 mmol) in H2O (1 mL). The resulting solution was stirred at room temperature for 14 hours. The organic layer was separated, dried over MgS0 ₄ and evaporated. The residue was purified by semi- preparative HPLC (MeCN/H20 gradient) to afford Im6 as a white solid (18.3 mg, 0.059 mmol, 17%).

¾ NMR (400 MHz, DMSO-de, δ ppm): 9.29 (br. s., 1 H), 8.38 (s, 1 H), 7.89 (d, / = 9.0 Hz, 2 H), 7.54 (d, J = 8.2 Hz, 2 H), 7.07 - 6.93 (m, J = 6.5, 8.5 Hz, 4 H), 2.22 (s, 3 H). ¹³ C NMR (100 MHz, DMSO-de, δ ppm): 172.2, 161.1 , 158.8, 138.5, 129.9, 128.8, 125.3, 123.7, 117.9, 116.4, 102.1, 20.4.

Im 8 (comparative): ((4-(ethoxycarbonyl)phenyl)carbamoyl)(2-(4-hydroxyphenyl)-l, 2,3- oxadiazol-2-ium-5-yl)ami

To a solution of ethyl 4-isocyanatobenzoate (67 mg, 0.351 mmol) and iminosydnone ImO-1 (75 mg, 0.351 mmol) in THF (5 mL) was added a solution of NaHC03 (1 eq., 30 mg, 0.35 mmol) in H2O (1 mL). The resulting solution was stirred at room temperature for 14 hours. The organic layer was separated, dried over MgS04 and evaporated. The residue was purified by semi-preparative HPLC (MeCN/EhO gradient) to afford Im 8 as a yellow solid (16.1 mg, 0.044 mmol, 13%).

¾ NMR (400 MHz, DMSO-de, δ ppm): 10.60 (br. s., 1 H), 9.82 (s, 1 H), 8.49 (s, 1 H), 7.91 (d, J = 9.0 Hz, 2 H), 7.84 (d, J = 8.8 Hz, 2 H), 7.77 (d, / = 8.8 Hz, 2 H), 7.02 (d, / = 9.0 Hz, 2 H), 4.27 (q, J = 7.0 Hz, 2 H), 1.30 (t, J = 7.0 Hz, 3 H).

¹³ C NMR (100 MHz, DMSO-de, δ ppm): 172.4, 165.5, 161.1 , 158.6, 145.6, 130.0, 125.2, 123.7, 122.1 , 117.0, 1 16.3, 102.6, 60.0, 14.2.

MS (ESI) m/z: 369.2 [M+H] ⁺ . Im 7: (2-(4-carboxyphenyl)-l,2,3-oxadiazol-2-ium-5-yl)(p-tolylcarb amoyl)amide

To a solution of p-tolyl isocyanate (15 mg, 0.1 13 mmol) and iminosydnone ImO-2 (27 mg, 0.113 mmol) in THF (5 mL) was added a solution of NaHCCb (1 eq., 10 mg, 0.12 mmol) in H2O (1 mL). The resulting solution was stirred at room temperature for 14 hours. The organic layer was separated, dried over MgS0 ₄ and evaporated. The residue was purified by semi- preparative HPLC (MeCN/EkO gradient) to afford Im 7 as a yellow solid (8.6 mg, 0.025 mmol, 22%).

¾ NMR (400 MHz, DMSO-de, δ ppm): 9.41 (br. s., 1 H), 8.69 (s, 1 H), 8.21 (s, 4 H), 7.53 (d, J = 8.1 Hz, 2 H), 7.04 (d, J = 8.1 Hz, 2 H), 2.22 (s, 3 H).

1 ³ C NMR (100 MHz, DMSO-de, δ ppm): 171.8, 165.9, 157.9, 138.1 , 136.5, 134.5, 131.0, 130.2, 128.8, 122.6, 1 18.1, 103.5, 20.3.

MS (ESI) m/z: 339.1 [M+H] ⁺ .

Iml3: (3-(4-carboxyphenyl)-l,2,3-oxadiazol-3-ium-5-yl)((2-(3-(2,5- dioxo-2,5-dihydro-lH- pyrrol-l-yl)propanamido)ethyl)carbamoyl)amide

The following synthesis process was conducted to prepare the above compound, referred to :

Step (a): synthesis of G - ((2-((tert-butoxycarbonyl)amino)ethyl)carbamoyl)(3-(4- iodophenyl)-l,2,3-oxadiazol-3-ium-5-yl)amide

To a suspension of 5-amino-3-(4-iodophenyl)-l,2,3-oxadiazol-3-ium chloride and NaHCCb in dry DMF (1 mL) was added the tert-butyl (2-isocyanatoethyl)carbamate. The mixture stirred at room temperature overnight. The mixture was quenched with NH4C1 (15 mL) then extracted with AcOEt. The combined organic layers were dried (MgS04) and concentrated under reduced pressure. The crude material was though flash chromatography.

¾ NMR (CDCb, 400MHz, ppm): δ = 8.14 (s, 1H), 7.98 (d, J =8.4 Hz, 2H), 7.52 (d, J = 8.4 Hz, 2H), 5.77 (bs, 1H), 5.07 (bs, 1H), 3.40-3.36 (m, 2H), 3.30-3.26 (m, 2H), 1.42 (s, 9H); ¹³ C NMR (CDCb, 101MHz, ppm): δ = 172.6, 161.9, 156.1 , 139.6 (2C), 133.5, 122.7 (2C), 101.7, 99.2, 79.2, 41.0, 40.0, 28.3 (3C) ;

IR (v, cm ^"1 ): 3283, 2976, 1691 , 1599, 1632, 1515, 1430, 1365, 1274, 1220, 1007, 959;

MS (ESI) m/z : [M+H] ⁺ = 474.2.

Step (b): synthesis of H - ((2-((tert-butoxycarbonyl)amino)ethyl)carbamoyl)(3-(4- (ethoxycarbonyl)phenyl)-l, -oxadiazol-3-ium-5-yl)amide

((2-((tert-butoxycarbonyl)amino)ethyl)carbamoyl)(3-(4-iodoph enyl)-l,2,3-oxadiazol-3-ium-5- yl)amide (45 mg, 0.095 mmol, 1 equiv.) was dissolved in a mixture of absolute EtOH (1 mL) and triethylamine (1 mL). [PdCh(PPh3)2] (6.3 mg, 0.009 mmol, 10 mol%) was added and the reaction mixture was kept under a CO atmosphere for 15 h and heated at 45 °C. The resulting suspension was cooled to room temperature and filtred through Celite eluting with ethyl acetate, and the inorganic salts were removed. The filtrate was concentrated and purification of the residue by silica gel column chromatography gave the desired product.

¾ NMR (CDCb, 400MHz, ppm): δ = 8.31 (d, J = 8.6 Hz, 2H), 8.20 (s, 1H), 7.88 (d, J = 8.6 Hz, 2H), 5.76 (bs, 1H), 5.03 (bs, 1H), 4.45 (q, J = 7.1 Hz, 2H), 3.40-3.36 (m, 2H), 3.30-3.25 (m, 2H), 1.45-1.41 (m, 12H);

¹³ C NMR (CDCb, 101MHz, ppm): δ = 172.5, 164.4, 161.7, 156.1 , 136.7, 134.5, 131.5 (2C), 121.4 (2C), 102.1 , 79.1, 61.9, 41.0, 40.4, 28.3 (2C), 14.2 ;

IR (v, cm ^"1 ): 3288, 1978, 1713, 1635, 1604, 1512, 1441 , 1366, 1274, 1173, 1108, 958, 770 ; MS (ESI) m/z : [M+H] ⁺ = 420.1 ;

Mp: 139-141 °C.

Step (c): synthesis of I - ((2-((tert-butoxycarbonyl)amino)ethyl)carbamoyl)(3-(4- carboxyphenyl)-l,2,3-oxadiazol-3-ium-5-yl)amide

To a solution of ((2-((tert-butoxycarbonyl)amino)ethyl)carbamoyl)(3-(4- (ethoxycarbonyl)phenyl)-l ,2,3-oxadiazol-3-ium-5-yl)amide (65 mg, 0.155 mmol) in EtOH (1 mL) /THF (1 mL) was added NaOH (5 eq). The resulting suspension was stirred at room temperature. After 2h, the mixture was diluted with water then extracted with AcOEt (3 times). The aqueous phase was acidified with HCl (2 N) until pH ca. 2. Then it was extracted with AcOEt (3 times). The combined organic layers were dried (MgS04) and concentrated under reduced pressure to give the desired product.

¾ NMR (DMSO, 400MHz, ppm): δ = 9.35 (s, 1H), 8.10 (d, J = 8.4 Hz, 2H), 7.99 (d, J = 8.4 Hz, 2H), 6.94 (t, J = 5.2 Hz, 1H), ;

¹³ C NMR (DMSO, 101MHz, ppm): δ = 172.2, 167.7, 161.3, 156.0, 141.3, 135.2, 131.0 (2C), 121.9 (2C), 102.6, 78.0, 40.5, 39.2, 9.6 (3C);

MS (ESI) m/z : [M+H] ⁺ = 392.3. Step (d): synthesis if J - ((2-ammonioethyl)carbamoyl)(3-(4-carboxyphenyl)-l,2,3- oxadiazol-3-ium-5-yl)amide 2,2,2-trifluoroacetate

To a solution of ((2-((tert-butoxycarbonyl)amino)ethyl)carbamoyl)(3-(4-carbox yphenyl)- l,2,3-oxadiazol-3-ium-5-yl)amide (1 equiv.) in DCM (2 mL) was added TFA (0.5 mL). The resulting solution was stirred at room temperature. After 4h, the solvent was evaporated under reduced pressure (with re-solubilisation in MeOH and re-evaporation 2 times in order to achieve full elimination of TFA).

¾ NMR (MeOD, 400MHz, ppm): δ = 9.21 (s, 1H), 8.37 (d, J = 8.4 Hz, 2H), 8.20 (d, J = 8.4 Hz, 2H), 3.20-3.10 (m, 4H);

MS (ESI) mJz : [M+H] ⁺ = 292.1.

Step (e): synthesis of K = Iml3

To a homogeneous solution of ((2-ammonioethyl)carbamoyl)(3-(4-carboxyphenyl)-l ,2,3- oxadiazol-3-ium-5-yl)amide 2,2,2-trifluoroacetate (1 equiv.) in dry DMF (1 mL) was added TEA (3 equiv.). The mixture was cooled at 0 °C and then 2,5-dioxopyrrolidin- 1 -yl 3-(2,5-dioxo- 2,5-dihydro-lH-pyrrol-l-yl)propanoate (1 equiv.) was added to the mixture. After 18h, the mixture was concentrated under vacuum. The residue was dissolved in EtOAc (100 mL) and extracted with 0.1 N HCl (2x). The organic layer was washed with brine (2x) and dried (Na2S04) and concentrated to give the desired product.

¾ NMR (MeOD, 400MHz, ppm): δ = 9.27 (s, 1H), 8.39 (d, J = 8.6 Hz, 2H), 8.23 (d, J = 5.6 Hz, 2H), 6.81 (s, 2H), 3.78 (t, J = 6.7 Hz, 2H), 3.37-3.32 (m, 4H), 2.46 (t, J = 6.7 Hz, 2H); MS (ESI) m z : [M+H] ⁺ = 443.1. Iml4: ((4- (cyanoethynyl)phenyl)carbamoyl)(3- (4- (ethoxycarbonyl)phenyl)- 1 ,2,3- oxadiazol-3-ium-5-yl)amide

This compound was prepared according to a process comprising the following successive steps.

Step 1: Synthesis of2-((4-iodophenyl)amino)acetonitrile

To a 250 mL round bottom flask was charged with 4-iodoaniline (5 g, 22.83 mmol, 1 equiv.), Nal (3.42 g, 22.83 mmol, 1 equiv.), K2CO3 (3.7 g, 27.39 mmol, 1.2 equiv.) and MeCN (60 mL) was added dropwise chloroacetonitrile (2.86 mL, 45.65 mmol, 2 equiv.) the mixture was stirred at reflux under nitrogen atmosphere.

After 48h, the mixture was allowed to cool at room temperature and filtered through a fritted glass filter with AcOEt (200 mL). The solution was then washed with NaClsat (100 mL). The combined organic layers were dried (MgS04) and concentrated under reduced pressure. The resulting material was purified though flash chromatography (100% cyclohexane to 80% cyclohex : 20% AcOEt) to afford 5.46 g (21.16 mmol, 92% yield) of analytically pure compound.

¾ NMR (CDCb, 400MHz, ppm): δ = 7.52 (d, / = 8.8 Hz, 2H), 6.48 (d, J = 8.8 Hz, 2H), 4.07 (s, 2H);

¹³ C NMR (CDCb, 101MHz, ppm): δ = 144.6, 138.2 (2H), 116.5, 115.7 (2H), 81.5, 32.4; MS (ESI) m/z : [M+H] ⁺ = 259.0 ; Step 2: Synthesis of 5-amino-3-(4-iodophenyl)-l,2,3-oxadiazol-3-ium chloride e

To a solution of 2-((4-iodophenyl)amino)acetonitrile (3.5 g, 13.56 mmol, 1 equiv.) in THF (20 mL) stirred at room temperature was added dropwise isopentyl nitrite (5.5 mL, 40.68 mmol, 3 equiv.). The mixture was stirred until full conversion to the corresponding nitroso aniline was achieved (TLC monitoring). Afterword, the solvent was evaporated to dryness under high vacuum to eliminate the excess of nitrite. Then the residue was dissolved in dry THF (10 mL) and a solution of dry HC1 in dioxane 4 M (34 mL, 10 equiv.) was added. The mixture was stirred at room temperature. After 16h, the precipitate formed was filtered and washed with EteO (150 mL) to afford analytically pure product.

¾ NMR (DMSO, 400MHz, ppm): δ = 10.10 (s, 2H), 8.69 (s, 1H), 8.14 (d, / = 8.4 Hz, 2H), 7.84 (d, J = 8.4 Hz, 2H);

¹³ C NMR (DMSO, 101MHz, ppm): δ = 169.4, 139.1 (2C), 132.4, 124.4 (2C), 102.3, 101.5; MS (ESI) m/z : [M-Clf = 288.2.

Step3: Synthesis of(tert-butoxycarbonyl)(3-(4-iodophenyl)-l,2,3-oxadiazol-3-i um-5-yl)amide

To a solution of 5-amino-3-(4-iodophenyl)-l,2,3-oxadiazol-3-ium chloride (4.08 mmol, 1 equiv.), NaHC0 ₃ (6.12 mmol, 1.5 equiv.) and DMAP (0.41 mmol, 10 mol%) and THF (30 mL) was added dropwise di-tert-butyl dicarbonate (6.12 mmol, 1.5 equiv.). The resulting mixture was stirred at room temperature for 48h. The heterogeneous mixture was quenched with NH4CI (35 mL) and extracted with AcOEt (3* 30 mL). The combined organic layers were dried over MgS04 and concentrated under reduced pressure. The crude material was purified though automated flash chromatography (from 100% cyclohexane to 80% cyclohexane / 20% AcOEt) to afford 1.36 g (3.51 mmol, 86% yield) of analytically pure compound.

¾ NMR (CDCb, 400MHz, ppm): δ = 8.10 (s, 1H), 7.98, (d, / = 8.7 Hz, 2H), 7.52 (d, J = 8.7, 2H) 1.51 (s, 9H);

¹³ C NMR (CDCb, 101MHz, ppm): δ = 174.3, 160.2, 139.7 (2C), 133.3, 122.7 (2C), 102.3, 99.48, 79.4, 28.1 (3C);

IR (v, cm ^"1 ): 3170, 3092, 2973, 1783, 1752, 1660, 1596, 1580, 1488, 1364, 1291, 1048, 1005, 964, 826, 728;

MS (ESI) m/z : [M+H] ⁺ = 388.1 ;

Mp: 134-136 °C.

Step 4: Synthesis of (tert-b toxycarbonyl)(3-(4-(ethoxycarbonyl)phenyl)-l,2,3-oxadiazol-3 - ium-5-yl)amide

(tert-butoxycarbonyl)(3-(4-iodophenyl)-l,2,3-oxadiazol-3- ium-5-yl)amide (300 mg, 0.774 mmol, 1 equiv.) was dissolved in a mixture of absolute EtOH (2.5 mL) and triethylamine (2.5 mL). [PdCh.(PPh3)2] (81 mg, 0.1 16 mmol, 15 mol%) was added and the reaction mixture was kept under a CO atmosphere for 2.5 h and heated at 60 °C.

The resulting suspension was cooled to room temperature and filtred through Celite eluting with ethyl acetate, and the inorganic salts were removed. The filtrate was concentrated and purification of the residue by silica gel column chromatography gave the desired product. The resulting residue was purified by chromatography (from 100% cyclohexane to 70% cyclohexane / 30% AcOEt) to afford 183 mg (0.550 mmol, 71% yield) of analytically pure compound.

¾ NMR (CDCb, 400MHz, ppm): δ = 8.29 (d, J = 9.0 Hz, 2H), 8.16 (s, 1H), 7.87 (d, J = 9.0 Hz, 2H), 4.43 (q, / = 7.0 Hz, 2H), 1.51 (s, 9H), 1.42 (t, J = 7.0 Hz, 3H); ¹³ C NMR (CDCb, 101MHz, ppm): δ = 174.6, 164.3, 160.6, 136.6, 134.7, 131.6 (2C), 121.4 (2C), 102.5, 79.2, 62.0, 28.1 (3C), 14.2;

IR (v, cm ^"1 ): 3159, 2979, 1784, 1716, 1662, 1586, 1366, 1271, 1152, 1106, 1048, 1007, 963, 855, 769, 728, 689;

MS (ESI) m z : [M+H] ⁺ = 334.3 ;

Mp: 151-153 °C.

Step 5: Synthesis of ((4-(cyanoethynyl)phenyl)carbamoyl)(3-(4-(ethoxycarbonyl)phe nyl)- l,2,3-oxadiazol-3-ium-5-yl)amide

To a solution of (tert-butoxycarbonyl)(3-(4-(ethoxycarbonyl)phenyl)-l ,2,3-oxadiazol-3-ium-5- yl)amide (91 mg, 0.273 mmol) in DCM (5 mL) was added TFA (0.5 mL). The mixture was stirred at room temperature for 3 hours. After it was reached full de-protection (monitoring by LCMS), the solvent was evaporated under reduced pressure (with re-solubilisation in MeOH and re-evaporation 2 times in order to achieve full elimination of TFA). In a separate flask, to a heterogeneous solution of triphosgene (0.33 equiv.) and 3-(4-aminophenyl)prop-2-ynenitrile (1 equiv.) in DCM (2 mL) was added, drop-wise at 0 °C, an aqueous solution of NaHCCb (3 equiv. inl .5 mL of water). The mixture was stirred at r.t. for 30 min, then the deprotected amine derivative was added in DCM. The mixture was stirred at room temperature. After 18h, the yellow heterogeneous mixture was diluted in Et20 (50 mL) and filtered. The yellow ppt was washed with Et20, collected and dried under vacuum, to afford the desired product in 44 % yield. ¾ NMR (DMSO, 400MHz, ppm): δ = 9.98 (s, 1H), 8.72 (s, 1H), 8.23-8.22 (m, 4H), 7.77 (d, J = 8.5 Hz, 2H), 7.67 (d, J = 8.5 Hz, 2H), 4.37 (q, J = 7.0 Hz, 2 H), 1.34 (t, J = 7.0, 3H);

IR (v, cm ^"1 ): 3345, 3144, 2256, 1697, 1651 , 1571 , 1616, 1513, 1491 , 1431, 1311, 1279, 1241 , 1179, 1009, 931, 836, 535 ;

MS (ESI) m/z : [M+H] ⁺ = 402.1.

Step 6: Synthesis of lml - (3-(4-carboxyphenyl)-l,2,3-oxadiazol-3-ium-5-yl)((4- (cyanoethynyl)phenyl)carbamoyl)amide.

To a solution of ((4-(cyanoethynyl)phenyl)carbamoyl)(3-(4-(ethoxycarbonyl)phe nyl)-l ,2,3- oxadiazol-3-ium-5-yl)amide (55 mg, 0.15 mmol) in EtOH (1 mL) /THF (1 mL) was added NaOH (5 eq). The resulting suspension was stirred at room temperature. After 2h, the mixture was diluted with water then extracted with AcOEt (3 times). The aqueous phase was acidified with HCl (2 N) until pH ca. 2. Then it was extracted with AcOEt (3 times). The combined organic layers were dried (MgS04) and concentrated under reduced pressure to give the desired product in 7% yield. ¾ NMR (DMSO, 400MHz, ppm): δ = 9.98 (s, 1H), 8.72 (s, 1H), 8.13-8.02 (m, 4H), 7.77 (d, J = 8.5 Hz, 2H), 7.67 (d, J = 8.5 Hz, 2H).

MS (ESI) m/z : [M+H] ⁺ = 374.2. Example 2: Kinetic study of the reaction of iminosydnones with cyclic alkynes

Experimental:

Reactions of iminosydnones Im 2 and Im 5 as described in Table 1 below with tetramethylthiacycloheptyne (TMTH) was carried out in PBS buffer (0.1M, pH 7.4) at 100 μΜ concentration of iminosydnone and 150 μΜ concentration of cyclooctyne TMTH using the following procedure:

To 900 μΤ of PBS buffer were added 10 μί of the solution of benzamide (internal standard, 100 mM in DMSO), 1 μΐ, of the solution of iminosydnone (100 mM in DMSO) and 1.5 μΐ, of the solution of TMTH (100 mM in DMSO). The reaction mixture was injected in HPLC and the conversion was followed by measuring the normalized iminosydnone peak area.

Results:

Figures 1 and 2 present the HPLC monitoring of the reaction between the cyclic alkyne TMTH and iminosydnones Im5 and Im 2, respectively. The reaction has been conducted at 100 μΜ in PBS buffer (pH 7.4). The results indicated an almost complete reaction after 30 min proving that the reaction is fast enough to be useful for bioconjugation and release applications. The presence of a F group on the phenyl group would clearly not detrimentally affect these results. One can expect similar or even improved kinetics for the iminosydnones according to the invention.

Example 3: Kinetic study of different iminosydnones

The kinetics of the coupling reaction of different iminosydnones with two cyclic alkynes was studied, according to the following scheme.

Experimental:

Reactions of iminosydnones with BCN (Biclyclononyne) or TMTH were carried out in PBS/DMSO (9: 1) mixtures at 100 μΜ concentration of sydnones and 150 μΜ concentration of BCN or TMTH using the following procedure:

To 900 μΐ, of phosphate buffered saline (PBS, 100 mM) was added 87.5 μΐ, of DMSO, 10 jiL of the solution of benzamide (internal standard, 100 mM in DMSO), 1 μϊ _^ of the solution of iminosydnone (100 mM in DMSO) and 1.5 μΐ, of the solution of BCN or TMTH (100 mM in DMSO). The reaction mixture was injected in HPLC every 30 min and the conversion was followed by measuring the normalized sydnone peak area.

Results:

Table 1 below presents the kinetic constant values K for these reactions, depending on the Ar group, the R group and the X group. Only iminosydnones 7, 13 and 14 are according to the invention.

Mai*: maleimide Table 1. K unit is M ^_1 .sec ^_1 , n.d. = not determined. Reactions were conducted with 100 μΜ of iminosydnones and 150 μΜ of BCN or TMTH in PBS 0.1 M (pH 7.4) containing 10% DMSO It can be seen that Im7, which is according to this invention, provides a higher kinetic constant value, both with BCN and with TMTH, than similar iminosydnones which bear either no F group (see Im5) or a different F group (see Im6). These results further show that the iminosydnones comprising a carbamate function at F' position (compare Iml l with Im3) and the iminosydnones comprising a halogen atom in position 4 (compare Im9 with ImlO and Iml 1 with Iml 2) afford the fastest reactions. In particular, 4-bromo-6-carbamate iminosydnones were found to react with the cyclooctyne BCN with a constant of 0.15 M^.sec ^"1 which allows the reaction to proceed at concentration as low as 1 μΜ.

Second order reaction rate was determined by plotting ln([A]/[B])/([A] - [B]) versus time and analyzing by linear regression (Equation). Second order rate constant corresponds to the determined slope.

= kt + const

Equation. [A] - concentration of iminosydnones (M); [B] - concentration of BCN (M); t - reaction time (sec); k - reaction rate (M ¹ · sec ^"1 )

Linear regression curves for sydnones Im2, Im6 and Im7 are illustrated in figures 2 and 3.