The present invention relates to certain chelating agents, in particular aminopoly(carboxylic acid or carboxylic acid derivative) compounds, and to the salts and chelates thereof.

The medical use of chelating agents is well established, for example as stabilizers for pharma¬ ceutical preparations, as antidotes for poisonous heavy metal species and as diagnostic agents for the administration of metal species (e.g. ions or atoms) for diagnostic techniques such as X-ray, magnetic resonance imaging (MRI) or ultrasound imaging or scintigraphy.

Aminopoly(carboxylic acid or carboxylic acid derivative) (hereinafter APCA) chelating agents and their metal chelates are well known and are described for example in US-A-2407645(Bersworth) , US-A-2387735 (Bersworth), EP-A-71564 (Schering) , EP-A-130934 (Schering) , EP-A-165728 (Nycomed AS) , DE-A-2918842 (Rexolin Chemicals AB) , DE-A-3401052 (Schering) , EP-A-258616 (Salutar) , EP-A-277088 (Schering), DE-A-3633243 (Schering), EP-A-287465 (Guerbet) and EP-A-292689 (Squibb) . Cyclic APCAs are also well known in the art, for example from EP-A-287465 (Guerbet) and US-A-4639365 (Sherry) .

EP-A-71564, for example, describes paramagnetic metal chelates, for which the chelating agent is nitrilotriacetic acid (NTA) , N,N,N' ,N'-ethylenediamine- tetraacetic acid (EDTA) , N-hydroxyethyl-N,N' ,N'- ethylenediamine-triacetic acid (HEDTA) , N,N,N' ,N",N"- diethylenetriamine-pentaacetic acid (DTPA) and N-hydroxyethylimino-diacetic acid, as being suitable as contrast agents for MRI, contrast being achieved by the effect of the magnetic field of the paramagnetic species (e.g. Gd(III)) with the chelating agents serving to reduce the toxicity and to assist administ-

ration of that paramagnetic species.

Amongst the particular metal chelates disclosed by EP-A-71564 was Gd DTPA, the use of which as an MRI contrast agent has recently received much attention. The Gd(III) chelate of 1,4,7,10-tetra- azacyclododecanetetraacetic acid (DOTA) , referred to in DE-A-3401052 (Schering) and in US-A-4639365 (University of Texas) , lias also recently received attention in this regard.

To improve stability, water solubility and selectivity, relative to the APCA chelating agents described in EP-A-71564, Schering, in EP-A-130934, have proposed the partial substitution for the N-attached carboxyalkyl groups of alkyl, alkoxyalkyl, alkoxycarbony alkyl or alkylaminocarbonylalkyl groups, where any amide nitrogens may themselves carry polyhydroxyalkyl groups.

However, all hitherto known APCA chelating agents and their metal chelates encounter problems of toxicity, stability or selectivity and there is thus a general and continuing need for APCA chelating agents which form metal chelates of reduced toxicity or improved stability.

To achieve reduced toxicity, Nycomed, in EP-A-299795 have proposed APCAs which carry hydrophilic groups on the amine nitrogens or on the alkylene chains linking the amine nitrogens.

Viewed from one aspect, the present invention provides compounds of formula I

X-CHR ¹ -NZ-(CHR ¹ )n-A-(CHR ¹ )m-NZ-CHR ¹ -X (I)

- or a group N-Y;

A iiss aa ggrroouupp NN--'Y or A-(CHR ) - represents a carbon- nitrogen bond or, when the groups Z together are

a group -(CHR ) -A'-(CHR )_-, A may also represent an oxygen or sulphur atom; each Y, which may be the same or different, is a a group -(CHR ¹ ) N (CHR ¹ X) _ or a group CHR ¹ X; each X, which may be the same or different, is a

R 1 group or a group of formula COD, POD-, CO (OH) ?,

S0 ₂ D, CH ₂ SR ² , CS ₂ R ² or CSD; each D which may be the same or different is a group of formula OR 2, NR2 ₂ or

where each R which may be the same or different is a hydrogen atom, a hydroxyl group or an optionally hydroxylated alkyl group, s is 0, 1 or 2, and is a group CHR , NR or an oxygen atom; each R , which may be the same or different, is a hydrogen atom, a hydroxyalkyl group or an optionally hydroxylated alkoxy or alkoxyalkyl group; n,m,p,q and r are each 2,3 or 4, preferably 2;

2 each R which may be the same or different is a hydrogen atom, an optionally mono or polyhydroxylated alkyl, alkoxyalkyl or polyalkoxyalkyl group; with the provisos that where s is 0 then in the resulting 5 membered ring is a CHR 11 group _} at least one nitrogen carries a -CHR,X moiety wherein

X and R are not the same, that at least one group

X is other than a group R or COD, and that unless the groups Z together are a -(CHR ) -A'-(CHR ) group or *A is an N-(CHR1) - N(CHRϊX- ^g ) ₂ group at ^r

least one R is other than hydrogen) and salts and metal chelates thereof.

In the compounds of the invention, alkyl or alkylene moieties in the R 1, R2 and R11 groups may, unless otherwise stated, be straight-chained or branched and preferably contain from 1 to 8, especially preferably from 1 to 6 and most preferably 1 to

4, carbon atoms. Where ^' substituents may optionally be substituted by hydroxyl or alkoxy groups, this may be mono-substitution or polysubstitution, and in the case of poly-substitution the hydroxyl or alkoxy substituents may be carried by alkoxy substituents groups.

Where a group D in a compound according to the invention is a nitrogen-attached heterocyclic ring, it particularly preferably is of formula:

Particularly preferred compounds of formula I include those of formula la

X-CHR α- „N„Z-(CHR ι _λ ) ₂ - „N,Y,-( ₍ C _Λ H_R„L) ₂ ~ „N„Z-C _. _τ H _τ _R,ι-X (la)

(wherein each group Z is a group -CHR X or the groups Z together are a group -(CHR ) ₂ -A'-(CHR ) ₂ ~; each Y, which may be the same or different, is a group -(CHR ¹ ) ₂ -N(CHR ¹ X) ₂ or -CHR X; and A ¹ ,X and R are as hereinbefore defined) and metal chelates and salts thereof.

In the compounds of the present invention, it is particularly preferred that one or more of the -CHR - groups in the bridges between the amine nitrogens, i.e. in the groups (CHR ) _n , (CHR ) _jn , (CHR ¹ ) , (CHR ¹ ) and (CHR ¹ ) , should carry a hydrophilic R group. Prior art APCAs, such as DTPA or DOTA for example, possess certain hydrophobic areas which cause the metal chelates produced from such chelating agents to present relatively lipophilic and hydrophobic zones.

In the compounds of formula I, each hydrophilic R group, which may be straight-chained or branched, preferably has a carbon atom content of from 1 to 8, especially preferably 1 to 6, carbon atoms. The R groups may be alkoxy, polyalkoxy, polyhydroxy- alkoxy, hydroxlated polyalkoxy, polyhydroxylated polyalkoxy, hydroxylated alkoxyalkyl, hydroxylated polyalkoxyalkyl, polyhydroxylated alkoxyalkyl or polyhydroxylated polyhydroxyalkyl groups, but more preferably they will be monohydroxyalkyl or polyhydroxyalkyl groups. The hydrophilic R groups serve to increase the hydrophilicity and reduce the lipophilicity of the metal chelates formed with the chelating agents of the invention and it is preferred that the compounds of formula I should contain at least 1, conveniently from 1 to 12, and preferably 1 to 4 hydrophilic R groups and that in total the hydrophilic R groups should contain about 6 or more hydroxy or ether oxygen atoms.

As hydrophilic R groups, the compounds of the invention may thus include for example hydroxy- methyl, 2-hydroxyethyl, 1,2-dihydroxyethyl, 3-hydroxy- propyl, 2,3-dihydroxypropyl, 2,3,4-trihydroxybutyl, 1-(hydroxymethyl)-2-hydroxy-ethyl, methoxymeth l, ethoxymethyl, 2-hydroxyethoxymethyl, methoxyethoxy- methyl, (2-hydroxy-ethoxy)ethyl, etc, groups.

The carboxyl derivatives which may be represented by the groups X in the compounds of the invention may include, for example, amide groups, ester groups and carboxyl groups, for example groups of formulae

-CONR 2R3 (wherein R2 is a hydrogen atom or an optionally hydroxylated alkyl, for example C, ,- alkyl, group and R 3 is a hydrogen atom, a hydroxyl group or an optionally hydroxylated alkyl group) ,

C0NiCH-CHR ^i:L W(CHR )SC/H--. (where W represents an oxygen atom or a group CH or CHOH, s is 0 or 1 and R 11 is hydrogen or where s is 1 and W is oxygen

R may also represent a C, . hydroxy-alkyl group) ,

-COOR (wherein R is an optionally hydroxylated alkyl group) . Compounds wherein all but one X group is a carboxyl or a salt or amide thereof are particularly preferred. Moreover compounds wherein terminal amine nitrogens, i.e those carrying two CHR X groups, carry a CHR X group in which

X is an amide are also preferred. Compounds of formula I wherein one or more X groups are carboxyl groups may form salts or chelate complexes, which are also compounds according to the present invention, in which one or more (but not necessarily all) such carboxyl groups are converted to -COOM groups

(wherein M is a monovalent cation or a fraction of a polyvalent cation, for example an ammonium or substituted ammonium ion or a metal ion, for example -_tn alkali metal or alkaline earth metal ion) . Particularly preferably, M is a cation deriving from an organic base, for example meglumine or lysine.

It is also particularly preferred that the number of the ion-forming groups X in the compounds of formula I be chosen to equal the valency of the metal species to be chelated by the compound formula I. Thus, for example, where Gd(III) is to be chelated, the chelating agent of formula I preferably contains three ion-forming X groups, for example -COOH or -COOM. In this way, the metal chelate will be formed as a neutral species, a form preferred since the osmotic pressures in concen¬ trated solutions of such compounds are low and since their toxicities relative to their ionic analogues are significantly reduced.

To improve complex stability and thereby reduce the toxicity of the complexes, use of other co plexing moieties than acetic acid residues may be advantageous. The choice of complexing groups will be dependent upon the metal and complex in accordance to the theory of hard and soft acids and bases (HSAB theory) .

Included amongst the particularly preferred chelating agents of formula I are the compounds of formulae lb, Ic, Id, Ie and If:

(XϊA-C) ₂ N-(CHR ³ ).,-N(CHirX) (lb)

(XR ¹ HC) ₂ N-(CHR ¹ ) ₂ -N-(CHR ¹ ) _.-N(CHR^) ₂

(Id) CHR 1-CHR1-N(CHR1X) -

CHR ¹ X CHR-'-X

CHR ¹ -N-CHR ¹ -CHR ¹ -N-CHR ¹

(wherein A' is oxygen or sulphur and at least one of the the X groups is other than a COD or R group, preferably wherein at least two, more preferably 3 or 4 of the X groups are ion-forming groups (for example -COOH or -COOM groups) , preferably wherein at least one and especially preferably at least two R groups are hydrophilic groups, and particularly preferably wherein at least one R group in each -(CHR ) ₂ moiety is a hydrophilic R group).

Preferred compounds of formula I include certain compounds of formulae lb to If wherein each moiety

-CHR ¹ X is of formula -CH_X" wherein X" is other than a group R 1. ^Δ

The following are particular examples of preferred compounds according to the invention

( HO_ - H ) ₂

( I i )

and chelates, especially Gd 3+ chelates, and salts,

-- e.g. Na salts, thereof.

Viewed from a further aspect, the invention provides a process for the preparation of the compounds of formula I, said process comprising one or more of the following steps:

(i) reacting a corresponding amine to introduce a -CHR X moieity at an amine nitrogen;

(ii) converting a carboxyl X moiety in a compound of formula I into a carboxyl derivative thereof or a carboxyl derivative X moiety in a compound of formula I into a carboxyl group; and

(iii) converting a compound of formula I into a salt or chelate thereof or converting a salt or chelate of a compound of formula I into a compound of formula I.

The introduction of a CHR X moiety at an amino function may for example be performed as follows:

a) To introduce a phosphonic acid moiety, the general method of synthesis of alpha-aminophosphonic acids described by K. Moedritzer et al. in J.Org.Chem. 31 (1966) 1603 may be used.

CH ₂ 0

R^ H R CH ₂ P0~H ₂

(ID (III)

(where R * ₂ NCHR1X is a compound of formula I)

b) To introduce a hydroxamic acid moiety, the general method for transformation of an activated acid derivative into hydroxamic acid described by P.N. Turowski et al. in Inorg. Chem. 2 _ (1988) 474 may be used.

(IV) (V)

(wherein R N(CH-COOH)CHR X is a compound of formula I).

c) To introduce a sulfonic acid moiety, synthesis may be performed by alkylation of an amino function for example with iodomethanesulfonic acid

R ₂ NH ICH ₂ S0 ₃ H R NCH ₂ S0 ₃ H

(ID (VI)

d) To introduce a thiol group, synthesis may be made by functional group transformation for example from corresponding alcohols by reaction with phosphorus pentasulfide (BP 917921) or from corresponding halides with KHS (see Chem.Ber j36_ (1953) 825).

R ₂ NCH ₂ CH ₂ 0H P-.S- R _j NCH _j CH^H

(VII) (VIII)

R ₂ NCH ₂ CH ₂ Br KHS R ₂ CH ₂ CH ₂ SH

(IX) (VIII)

e) To produce thiocarboxylic acids, dithiocarboxylic acids and derivatives thereof, carboxylic esters can be converted to both thioesters and dithioesters for example with phosphorus pentasulfide (see J.W Scheren: Synthesis (1973) 149) or Lawesson's reagents (see Cava et al.: Tetrahedron 41(22) (1985 5061).

R ⁺ -C0 OR ² P-S- R ⁺ -C0SR ²

(X) (XI)

R ⁺ COOR ² Lawesson's R ⁺ -C0SR ²

-» reagents

(X) (XI)

or R ⁺ -CSSR ²

(XII)

(where R X is a compound of formula I)

Lawesson's reagents may also be used in a general method for conversion of carboxamides into thiocaboxamides (see Catfa et al. : Tetrahedron 41 (22) (1985) 5061):

(XIII) (XIV)

Cyano groups may also be converted into thioesters or dithioesters (see Janssen: "The Chemistry of Carboxylic Acids and Esters", Ed. S. Patai, Interscience, N.Y., 1969, Chapter 15)

H ₂ S R ⁺ CN R ² X ² H R ⁺ -C(=NH ₂ )X ² R ² R ⁺ CS(X ² R ² )

__> ^

H Pyridine

(XV) (XVI) (XVII)

2 (where X represents an oxygen or sulphur atom) .

f) A carboxylic acid, CHR COOH, functional group may be introduced by reaction between an amine of formula II and for example a compound of formula XVIII

L CHR X'

(XVIII)

where L is a leaving group, for example a halogen

]_r atom such as chlorine, bromine or iodine, and R is a group R as described above or a group convertible thereto and X ¹ is a COOH moiety or a group convertible thereto.

Transformation of a carboxylic acid into a derivative thereof may readily be performed as described in the literature (e.g. by esterification, amide formation etc.).

In the preparation of the compounds of the invention, it may be desirable or necessary to protect functional groups such as carboxylic acids and alcohols in the starting compound, e.g. the amine of formula II. This might be done as described in the literature (see for example T. Greene, "Protective Groups in Organic Synthesis", John Wiley & Sons, 1981) .

For the protection of hydroxyl groups, particular mention may be made however of the utility of benzyl protecting groups which are stable over a wide pH range but are readily removed by hydrogenolysis as described by T.W. Greene. Polyhydroxyalkyl groups may for example alternatively be protected in the form of cyclic polyether groups, for example as 2,2-dimethyl-l,3-dioxa-cyclopent-4-yl groups, as such cyclic polyether groups can be opened by acid hydrolysis to leave the unprotected polyhydroxy¬ alkyl group.

Thus for example, introduction of a -CHR X moiety may be effected by reacting an amine of formula XIX

R ³ -N-(CHR ¹ ') _n -A"-(CHR ¹ ') _m -N-R ³ (II)

Z' Z'

(wherein R 3 is a hydrogen atom or a -CHR1'X3 group;

3 X is as defined for X or is a group convertible

1• thereto; R is as defined above; each group Z' is a group -CHR 1'X3 or an R3 moi.ety or together the groups Z' are a -(CHR ¹ ') -A'"-(CHR ¹ ') - bridging q ~- group where A"' is an oxygen or sulphur atom or

3 a group*-N-Y' where Y ¹ is an R moiety or a group

-(CHR ¹ ') -N(R ³ ),; and A" is a group -N-Y' or -A"-

(CHR ) - is a carbon-nitrogen bond or, where the groups Z ¹ together form a bridging group, A" may

also represent an oxygen or sulphur atom; with

3 the proviso that at least one R moiety is a hydrogen atom.

Thus for the process of step (i) the following preferred starting compounds of formula II may be used:

(lid)

1"

R .1"

NH ,1"

R 1"

,1"

,1" *

./✓

R ^■ -/ -R' (III)

R ¹ "

(wherein each R 1" is an optionally protected hydroxyalkyl or hydroxyalkoxyalkyl group, for example a -CH ₂ ~

0-CH_-Phenyl group or a 2,2-dimethyl-l,3-dioxa- cyclopent-4-yl group, A 2 is a sulphur or oxygen atom or a group -N-CHR 1'X3 and R6 is a group -CHR1'X3 or a moiety convertible thereto) . In the starting compounds of formulae Ha to Ho, optionally protected hydroxyalkyl groups attached to the alkylene chains between amine nitrogens are preferably benzyl protected groups and the nitrogen-attached protected hydroxyalkyl ggrroouuppss iinn --CCHHRR 1 1''XX33 mmooiieettiieeis are preferably in the form of cyclic polyethers.

The preparation of starting compounds of formulae Ha to Ho, may for example be by the following procedures:

Compounds of formula Ha may be prepared by the following scheme:

(4)

The starting compound (1) is described by A. Bongini et al. in J. Chem. Soc., Perkin Trans. 1, (1985) 935. It can be converted by benzyl protection of the remaining alcohol group and by ammonolysis to compound (2) and then condensation of compounds (1) and (2) and subsequent acid hydrolysis can yield compound (4) which is of formula Ha.

Compounds of formula lib may be prepared from compounds of formula Ha by reductive amination, for example as described by R.F. Borch in J. Org. Chem. 3_4 (1969) 627, using a protected aldehyde prepared for example as described by C. Hubschwerlen in Synthesis (1986) 962. The reaction may for example follow the scheme:

Compounds of formulae Hm and Hn may be prepared analogously to compounds of formulae Ha and lib by omitting the condensation step (b) in the above scheme.

Compounds of formula lie may be prepared analogously to compounds of formula Ha by condensation of compounds (1) and (2) and subsequent acid hydrolysis, for example according to the scheme:

Compounds of formulae Hm and Hn may be prepared analogously to compounds of formulae Ha and lib by omitting the condensation step (b) in the above scheme.

Compounds of formula He may be prepared analogously to compounds of formula Ha by condensation of compounds (1) and (2) and subsequent acid hydrolysis, for example according to the scheme:

' ^v

Compounds of formula Hd may be prepared analogously to compounds of formula lib by reductive amination of compounds of formula He, for example following the scheme:

Compounds of formula He may be prepared by the following scheme:

(11)

«

(12)

Compounds of formula Ilf may be prepared analogously to compounds of formula He using a triamide starting material:

The alpha-formylation described above may be performed using the method described in J. Med. Chem. 8 (1965) 220.

Alternatively, compounds of formulae He and Ilf may be prepared by replacing the formylation step (e) by reaction with chloromethylbenzylalcohol (available from Fluka) to yield the starting compounds (15) and (16) for the reduction step (f) :

The direct insertion of benzyl-protected hydroxymethyl groups may be performed as described in Org. Syn. 5_2 (1972) 16.

Compounds of formula Hg may be prepared by the following scheme:

R ¹ = -CH OCH Phenyl

(19)

R' R ^v

(k)

(18) halogenation / \

Hal HH Eal

(21 )

(1) ^• (21) ' ' →*- (20)

V^-Q

Compounds of formula (17) may be produced by mono-protection of aminopropandiol at the primary hydroxyl group and may be mono or di-alkylated using a glycidol ether. The mono and di-alkylation products may be separated by distillation. The mono-alkylation product, compound (18) , is used in the preparation of compounds of formula Ilg and the dialkylation product, compound (22) below, may be used in the preparation of compounds of formula Ilh. The mono-alkylated compound (18) may be converted to compound (20) , which is of formula Ilg, by oxidation and subsequent reductive amination or by halogenation and subsequent amination.

Compounds of formula Ilh may be prepared analogously to the compounds of formula Ilg, for example according to the scheme:

Compounds of formula Ho can be prepared analogously to compounds of formula Ilg by omitting the initial mono-/di-alkylation step (h) .

The cyclic compounds of formula Hi may be prepared by peptide condensation followed by reduction of the amide carbonyl groups, substantially as described by J. Tabushi et al. in Tetr. Lett. (1976) 4339 and (1977) 1049. The reaction may be performed according to the following scheme:

R ¹ R'

The starting compound (24) , wherein A is an amine group, may be prepared by alkylation of an iminodiacetic acid derivative and the ether and thioether. starting compounds may be prepared analogously by formylation of the corresponding starting materials, for example as described by

W. Rasshofer et al. in Chem. Ber. 112 (1979)

2095. Compounds of formula Hi are particularly preferred starting materials as they may be used to form non-ionic or mono-ionic chelates with trivalent

2 metal ions according to the selection of A .

- 25 -

The cyclic compounds of formula Hj may be prepared by the well known routes for the preparation of cyclic polya ines. Thus, in a method analogous to that described by J.E. Richmann et al. in J. Am. Chem. Soc. 96 ⁽ 1974) 2268, compounds of formula Ha may be tosylated and the resultant product may then be cyclized with a di (protected hydroxyalkyl ₎

e

_. (28)

Ms = methanes lphonyl Ts = tosyl Rr

R = -CH

Compound ⁽ 27 ⁾ may be prepared from compound ⁽ 18 ⁾ by a method analogous to that described by . Hediger et al. in J. Chem. Soc, Chem Commun ⁽ 1978) 14 and by J. Pless et .al. in Chem. Abs 71 ⁽ 1969 ^* ) 49569x. Various detosylation methods for step ⁽ p ⁾ are known, as described for example by . Rasshofer et al. in Liebigs Ann Chem. ₍ 1977 ₎ 1344. The group R ⁶ may be a protecting group resistant

to. the detosylation conditions allowing the possibility of substituting the nitrogen to which it is attached with a carboxymethyl derivative, etc.

Alternatively, a tetrapeptide or a protected tetrapeptide may be reduced, and the corresponding tetraamine may be cyclized in a way similar to that described by M.K.Mόi et al. in J.Am.Chem. Soc. 110 (1988) 6266.

t ^'

Compounds of formula Ilk may be prepared by a reaction scheme substantially as follows:

BOC

B _OC = t-butyloxycarbonyl R ^1' = -CH OCH^Phenyl

R' 0 (r)

-£»• (31-) diisobutylalvuninium

N MH OCH, hydride

BOC (35)

R* = -CH OCH-Phenyl

R' R '

(s)

(3f )

NH,

,N

NaCNBH, JH-Λ NH NH

3 BOC ^N B0C

CH OH (3 _ )

(reductive amination)

( 37 )

The starting compound (33) is described by Y. Ohfune et al. in Tetr. Lett. (1984) 1071. Protection of the alcohol function as a benzyl ether gives compound (34) which alternatively can be obtained by reducing the commercially available serine ester, compound (35) , as described in Chem. Pharm. Bull. 23 (1975) 3081. Reductive amination of compound (34) yields compound (36) from which the BOC (t- butyloxycarbonyl) groups may be removed by acid hydrolysis to yield compound (37) which is of formula Ilk. Compounds of formula Ilg may be prepared by alkylation of compounds of formula Ilk, for example with 2-(2,2-dimethyl-l,3-dioxa-cyclopent- 4-yl)-ethylamine. This reaction would generally be performed as a reductive amination.

28 -

The asymmetric compounds of formula III may be prepared by peptide condensation of protected a ino acids followed reduction of the amide carbonyl groups, for example using the following scheme:

Reductive amination of 0-benzyl serine with glyceraldehyde acetal gives compound (39) and coupling of compound ^° (39) with the ethyl ester of _O -benzyl protected ser ine gives the dipeptide compound ₍ 40 ₎ ⁽ see J. Martinez et al. Int . J. Peptide Protein Res . 12 ⁽ 1978 ) 277 ) . Amidation of compoun _d (40 ₎ with a protected amino alcohol gives compound ₍ 41 ₎ which may be reduced to compound (42) using lithium aluminium hydride , as described by J. E. Nordlander et al . in J. Org. Chem. 49_ (1984) 133. Compound ⁽ 42 ⁾ is a compound of formula III. if the amidation

step (w) is omitted, reduction of compound (40) will give further asymmetric compounds of formula II.

The cyclic compounds of formula I may also be prepraed by methods analogous to those described by Guerbet in EP-A-287465. Thus a compound of formula Hi may be formed by reacting a polyamine of formula (43)

T-N-(CHR ¹ ") ₂ - ^NT -(CHR ¹ ") ₂ -NT (43)

with an amine of formula (44)

L-(CHR ¹ ") ₂ -NY ³ -(CHR ¹ ") ₂ -L (44)

(where T represents a displaceable group such as a tosyl, mesyl or benzenesulphonyl group, L represent a leaving group such as a halogen atom, e.g. chlorine,

3 bromine or iodine, and Y represents a group T or CHR 1"X3) to yield a compound of formula Hi where A 2 is N-CHR1"X3. Subsequent reaction with an ether or thioether of formula (45)

L(CHR ¹ ") ₂ X ² -(CHR ¹ ") ₂ L (45)

2 (where X represents an oxygen or sulphur atom) can yield the corresponding cyclic ether or thioether.

Insertion of CHR X moieties in compounds of formulae Ha to Ho may be performed as described above to give compounds of formula I. However to insert different CHR X moieties in the same molecule it may be desirable or necessary to selectively protect different amine nitrogen, e.g. by conventional methods.

Chelants of formula I may be used as the basis for bifunctional chelants or for polychelant compounds, that is compounds containing several independant chelant groups, by substituting for one X or R group a bond or linkage to a macromolecule or polymer, e.g. a tissue specific biomolecule

or a backbone polymer such as polylysine or polyethyleneimi which may carry several chelant groups and may itself be attached to a macromolecule to produce a bifunctional-polychelant. Such macromolecular derivatives of the compounds of formula I and the salts and metal chelates thereof form a further aspect of the present invention.

The linkage of a compound of formula I to a macromolecule or backbone polymer may be effected by any of the conventional methods such as the mixed anhydride procedure of Krejcarek et al. (see Biochemical and Biophysical Research Communications 77: 581 (1977)), the cyclic anhydride method of Hnatowich et al. (see Science 220: 613 (1983) and elsewhere) , the backbone conjugation techniques of Meares et al. (see Anal. Biochem. 142: 68 (1984) and elsewhere) and Schering (see EP-A-331616 for example) and by the use of linker molecules as described for example by Nycomed in WO-A-89/06979.

Compounds of formula I thus produced may be converted by conventional techniques to salts or chelate complexes thereof.

The chelating agents of the present invention are particularly suitable for use in detoxification or in the formation of metal chelates, chelates which may be used for example in or as contrast agents for in vivo or in vitro magnetic resonance (MR) , X-ray or ultrasound diagnostics (e.g. MR imaging and MR spectroscopy) , or scintigraphy or in or as therapeutic agents for radiotherapy, and such metal chelates form a further aspect of the present invention.

Salts or chelate complexes of the compounds of the invention containing a heavy metal atom or ion are particularly useful in diagnostic imaging or therapy. Especially preferred are salts or complexes with metals of atomic numbers 20-32, 42-44, 49 and 57-83.

For use as an MR-diagnostics contrast agent, the chelated metal species is particularly suitably a paramagnetic species, the metal conveniently being a transition metal or a lanthanide, preferably having an atomic number of 21-29, 42, 44 or 57- 71. Metal chelates in which the metal species is Eu, Gd, Dy, Ho, Cr, Mn or Fe are especially preferred and Gd 3+, Mn2+ and Dy3+ are particularly preferred. For such use, the paramagnetic metal species is conveniently non-radioactive as radioactivity is a characteristic which is neither required nor desirable for MR-diagnostics contrast agents.

For use as X-ray or ultrasound contrast agents, the chelated metal species is preferably a heavy metal species, for example a non-radioactive metal with an atomic number greater than 37, preferably greater than 50, e.g. Dy 3+

For use in scintigraphy and radiotherapy, the chelated metal species must of course be radioactive and any conventional complexable radioactive metal isotope, such as 99mTc or 111In for example, may be used. For radiography, the chelating agent may be in the form of a metal chelate with for examplie 67„Cu.

For use in detoxification of heavy metals, the chelating agent must be in salt form with a physiologically acceptable counterion, e.g. sodium, calcium, ammonium, zinc or meglumine, e.g. as the sodium salt of the chelate of the compound of formula I with zinc or calcium.

Where the metal chelate carries an overall charge, such as is the case with the prior art Gd DTPA, it will conveniently be used in the form of a salt with a physiologically acceptable counterion, for example an ammonium, substituted ammonium, alkali metal or alkaline earth metal cation or an anion deriving from an inorganic or organic acid. In this regard, meglumine salts are particularly preferred.

Viewed from a further aspect, the present invention provides a diagnostic or therapeutic agent comprising a metal chelate, whereof the chelating entity is the residue of a compound according to the present invention, together with at least one pharmaceutical or veterinary carrier or excipient, or adapted for formulation therewith or for inclusion in a pharmaceutical formulation for human or veterinary use.

Viewed from another aspect, the present invention provides a detoxification agent comprising a chelating agent according to the invention in the form of a weak complex or salt with a physiologically acceptable counterion, together with at least one pharmaceutical or veterinary carrier or excipient, or adapted for formulation therewith or for inclusion in a pharmaceutical formulation for human or veterinary use.

The diagnostic and therapeutic agents of the present invention may be formulated with conven¬ tional pharmaceutical or veterinary formulation aids, for example stablizers, antioxidants, osmolality adjusting agents, buffers, pH adjusting agents, etc. and may be in a form suitable for parenteral or enteral administration, for example injection or infusion or administration directly into a body cavity having an external escape duct, for example the gastrointestinal tract, the bladder or the uterus. Thus the agent of the present invention may be in a conventional pharmaceutical administration form such as a tablet, capsule, powder, solution, suspension, dispersion, syrup, suppository, etc; however, solutions, suspensions and dispersions in physiologically acceptable carrier media, for example"water for injections, will generally be preferred.

Where the agent is formulated for parenteral administration, the carrier medium incorporating

the chelate or the chelating agent salt is preferably isotonic or somewhat hypertonic.

Where the diagnostic or therapeutic agent comprises a chelate or salt of a toxic metal species, for example a heavy metal ion, or atom, it may be desirable to include within the formulation a slight excess of the chelating agent, e.g. as discussed by Schering in DE-A-3640708.

For MR-diagnostic examination, the diagnostic agent of the present invention, if in solution, suspension or dispersion form, will generally contain the metal chelate at concentration in the range 1 micromole to 1.5 mole per litre, preferably 0.1 to 700mM. The diagnostic agent may however be supplied in a more concentrated form for dilution prior to administration. The diagnostic agent of the invention may conveniently be administered in amounts of from 10 -4 to 3 mmol of the metal species per kilogram of body weight, e.g. about 1 mmol Dy./kg bodyweight.

For X-ray examination, the dose of the contrast agent should generally be higher and for scintigraphic examination the dose should generally be lower than for MR examination. For radiotherapy and detoxification, conventional dosages may be used.

Viewed from a further aspect, the present invention provides a method of generating enhanced images of the human or non-human animal body, which method comprises administering to said body a diagnostic agent according to the present invention and generating an X-ray, MR-diagnostics, ultrasound or scintigraphic image of at least a part thereof.

Viewed from a further aspect, the present invention provides a method of radiotherapy practised on the human or non-human animal body, which method comprises administering to said body a chelate of a radioactive metal species with a chelating agent according to the invention.

Viewed from a further aspect, the present invention provides a method of heavy metal detoxifica¬ tion practised on the human or non-human animal body, which method comprises administering to said body a chelating agent according to the invention in the form of a weak complex or salt with a physiologically acceptable counterion.

Viewed from a yet further aspect, the present invention also provides the use of the compounds, especially the metal chelates, according to the invention for the manufacture of diagnostic or therapeutic agents for use in methods of image generation, detoxification or radiotherapy practised on the human or non-human animal body.

Viewed from a still further aspect, the present invention provides a process for the preparation of the metal chelates of the invention which process comprises admixing in a solvent a compound of formula I or a salt (e.g. the sodium salt) or chelate thereof together with an at least sparingly soluble compound of said metal, for example a chloride, oxide or carbonate.

Viewed from a yet still further aspect, the present invention provides a process for the prepara¬ tion of the diagnostic or therapeutic agent of the present invention, which comprises admixing a metal chelate according to the invention, or a physiologically acceptable salt thereof, together with at least one pharmaceutical or veterinary carrier or excipient.

Viewed from a yet still further aspect, the present invention provides a process for the prepara¬ tion of the detoxification agent of the invention, which comprises admixing a chelating agent according to the invention in the form of a salt with a physio¬ logically acceptable counterion together with at least one pharmaceutical or veterinary carrier or excipient.

The disclosures of all of the documents mentioned herein are incorporated by reference.

The present invention will now be illustrated further by the following non-limiting Example. All ratios and percentages given herein are by weight and all temperatures are in degrees Celsius unless otherwise indicated.

Example 1

2,6-Bishydroxymethyldiethylenetriaminepenta ( ethylenephosphonic acid)

1,5-Diamino-l,5-dibenzloxymethyl-3-azapentane (0.5g, 1.46 mmol) was dissolved in cone. HC1 (1 ml) , and an aqueous solution of phosphorous acid (0.72g/8.8 mmol) was added. The solution was heated to reflux temperature, and a 35% aqueous formaldehyde solution (1.4 ml/17.6 mmol) was added dropwise. The solution was kept at 100 °C for 30 minutes. The solvent was removed by evaporation and the residue was dissolved in ethanol/water and precipitated with isopropanol to give a yellow oil, identified as 2,6-bis(benzyloxymethyl)diethylenetriaminepenta(methylene¬ phosphonic acid) (FAB-MS, [M+l]=814). This product was dissolved in methanol/water, and 10% palladium on carbon (2.89 g) and ammonium formiate (0.68 g/10.8 mmol) was added. The mixture was stirred at 50 °C for three hours, and kept at ambient temperature overnight. The catalyst was filtered off, and the solution evaporated to dryness. The residue was dissolved in water and loaded on a strong cation exchanger and eluted with aqueous ammonia (6M) .

The title compound was isolated as a white powder. Yield 244, M.P. greater than 350 °C. "hl-NMR (90 MHz, D ₂ 0) : 2.2-3.0 pp (m) , 3.4-3.8 ppm (m) .

Example 2

4,8-Bishydroxymethyl-3,6 _r 9-triscarboxymethyl-3,6,9- triazaunedecane-l,ll-bis-(N-methylhydroxamic acid)

a) 4,8-Bisbenzyloxymethyl-3,6,9-triscarboxymethyl- 3,6,9-triazaunedecane-l,11-bis-(N-methylhydroxamic acid)

l,5-Bisbenzyloxy-l,5-bis (2,6-dioxomorpholino)-3- azapentan-3-aceticacid (0.20 g, 0.34 mmol) was dissolved in DMA (2 ml) and N-methylhydroxylamine (0.28 g, 3.4 mmol) in DMA (1.5ml) was added. The mixture was stirred at ambient temperature under nitrogen for 24 hours. The solvent was evaporated, and the product was isolated as a yellw oil. Yield 0.22 g, 95%. FAB/MS: 692 (M+l)

b) 4,8-Bishydroxymethyl-3,6,9-triscarboxymethyl- 3,6,9-triazaunedecane-l,ll-bis-(N-methylhydroxamic acid)

4,8-Bisbenzyloxymethyl-3,6,9-triscarboxymethyl- 3,6,9-triazaunedecane-1,11-bis-(N-methylhydroxamic acid) (0.23 g, 0.34 mmol) was dissolved in methanol (20 ml) and ammonium formiate (0.16 g, 2.5 mmol) was added. 10% palladium on carbon (0.44 g) was added under argon. The suspension was kept at 50°C for 3 hours, filtered and evaporated and the 4,8-bishydroxy-methyl-3,6,9-triscarboxymethyl-3,6,9- triazaunedecane-1,11-bis-(N-methylhydroxamic acid) was isolated. Yield: 0.15 g (90%). FAB/MS: 512 (M+l) .

Example β

l,5-Bisamino-l,5-bishydroxymethyl-3-azapentanepenta (methylphosphonic acid)

a) 1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentane- penta (methylphosphonic acid)

1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentane (0.20 g, 0.58 mmol) (prepared in acordance with WO-A-89/00557) was dissolved in 6M hydrochloric acid (1 ml) and phosphorous acid (0.48 g, 5.8 mmol) dissolved in water (1 ml) was added. The temperature was increased to 80°C and formaldehyde (37%) in water (0.35 g, 11.6 mmol) was added. The solvent was evaporated and the l,5-bisamino-l,5-bisbenzyloxymethyl- 3-azapentanepenta-(methylphosphonic acid) was isolated. Yield 0.47 g, 99%, FAB-MS: 814 (M+l).

b) 1,5-Bisamino-l,5-bishydroxymethyl-3-azapentanfe- penta (methylphosphonic acid)

1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentane- penta(methylphosphonic acid) (0.47 g, 0.58 mmol) is dissolved in methanol (20 ml) , and ammonium formiate (0.54 g, 8.6 mmol) is added. 10% palladium on carbon (1.5 g) is added under argon. The suspension is kept at 50°C for 6 hours, filtered and evaporated and the l,5-bisamino-l,5-bishydroxymethyl-3-azapentanpenta

(methylphosphonic acid) is isolated. FAB-MS: 634

(M+l) .

Example 4

l,5-Bisamino-l,5-bishydroxymethyl-3-azapentanepenta (methyl- sulphonic acid) , pentasodium salt

a) 1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentane- penta-(methylsulphonic acid) , pentasodium salt.

1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentan (0.3 g, 0.87 mmol) (prepared in accordance with WO-A-89/00557) was dissolved in 2ml 50% methanol

in water and sodiumhydroxymethylensulphonate (0.6 g, 4.457 mmol) was added. The mixture was stirred at 50 °C for 3 hours, the solvent was evaporated and the title product isolated. Yield: 0.8 g, 99%.

b) 1,5-Bisamino-l,5-bishydroxymethyl-3-azapentan_- penta(methylsulphonic acid), pentasodium salt.

1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentane- penta(methylsulphonic acid) (0.1 g, 0.11 mmol) was dissolved in methanol (20 ml) , and ammonium formiate (50 mg, 0.8 mmol) was added. 10% palladium on carbon (140 mg) was added under nitrogen. The suspension was kept at 50 °C for 3 hours, filtered and evaporated and the title product was isolated. Yield: 72 mg, 90 %. Melting pointy 350°C.

Example 5

Gadolinium (III) chelate of 4,8-bis(hydroxymethyl)- 3,6,9-triscarboxymethyl-3,6,9-triazaundecane-1,11- bis-(N-methylhydroxamic acid)

4,8-Bishydroxymethyl-3,6,9-triscarboxymethyl-3,6,9- triazaundecane-1,11-bis-(N-methylhydroxamic acid) (0.61 g, 0.12 mmol) was dissolved in water (5 ml), gadolinium (III) chloride (42 mg, 0.12 mml) was added and the pH was adjusted to 5 with 1M sodium hydroxide. The mixture was stirred at ambient temperature for 1 hour and the solvent evaporated. The residue was stirred in methanol, filtered, evaporated and the title product was isolated. Yield: 0.64 g (80 %) . Melting point 180-190°C.

Example 6

Dysprosium (III) chelate of 4,8-Bishydroxymethyl- 3,6,9-triscarboxymethyl-3,6,9-triazaundecane-1,11- bis-(N-methylhydroxamic acid).

4,8-Bishydroxymethyl-3,6,9-triscarboxymethyl-3,6,9- triazaundecane-1,11-bis(N-methylhydroxamic acid) (0.61 g, 0.12 mmol) was dissolved in water (5 ml), and dysprosium (III) oxide (22 mg, 0.06 mmol) was added. The suspension was stirred at 80 °C for 5 hours, filtered, the solvent was evaporated and the title product was isolated. Yield: 0.72 g, 90%. FAB/MS: 673 (M+l).

Example 7

Sodium salt of the tri-gadolinium (III) chelate of 1,5-bisamino-l,5-bisbenzyloxymethyl-3-azapentane- penta(methylphosphonic acid)

1,5-Bisamino-l,5-bisbenzyloxymethyl-3-azapentane- penta(methylphosphonic acid) (0.09 g, 0.14 mmol) is dissolved in water (10 ml) , the pH is adjusted to 6 with 0.1 M sodium hydroxide and gadolinium (III) oxide (0.078 g, 0.21 mmol) is added. The suspension is stirred at 80°C overnight, filtered and evaporated,.

Example 8

Preparation of a solution containing the gadolinium (III) chelate of 4,8-bis(hydroxymethyl)-3,6,9-tris- carboxymethyl-3,6,9-triazaunedecane-l,ll-bis-(N- methylhydroxamic acid)

The gadolinium(HI) chelate of 4,8-bis(hydroxymethyl)- 3,6,9-triscarboxymethyl-3,6,9-triazaunedecane-1,11- bis-(N-methylhydroxamic acid) (6.65 g, 10 mmol) (Example 5) was dissolved in 20 ml of distilled water. The solution was filtered, placed in a 20 ml vial and autoclaved. The solution contained 0.5 mmol gadolinium per ml.