GB2317176A - Aza-thiophosphinic acids such as ethylenediiminodimethylenebis(methylthiophosphinic acid) and metal complexes thereof, and their use as imaging agents - Google Patents

Abstract

Acyclic ligands of formula (1) wherein Alk 1 is a C 1-4 alkylene, cycloaliphatic or oxoalkyl chain optionally substituted by one or more aryl or optionally substituted C 1-6 alkyl groups; and R 1 and R 2 which may be the same or different is each a hydrogen atom or an optionally substituted straight or branched C 1-6 alkyl group; q is zero or an integer 1 or 2; R 3 and R 4 which may be the same or different is each an alkyl, alkoxyalkyl or aryl group each of which may be optionally substituted by alkyl, aloxyalkyl, aryl, halide, cyano, NO 2 , SO 3 H, CO 2 H, CO 2 R 1 , NH 2 , or NR 1 R 2 groups; X and Y which may be the same or different are either O or S as long as one is S and metal complexes and/or salts thereof, are described together with processes for their preparation and compositions containing them. The compounds and metal complexes are useful for imaging, such as in the diagnosis of disease states using gamma or position-emitting radioisotopes, (tomography).

Description

AZA-THIOPHOSPHINIC ACIDS AND METAL COMPLEXES THEREOF Field of the Invention This invention relates to aza-thiophosphinic acids, to metal complexes thereof, to processes for their preparation and to the use of the metal complexes as imaging agents in radioisotopebased tomography.

Background to the Invention An important part of clinical imaging techniques involves the use of complexed gamma or positron-emitting radioisotopes. In positron emission tomography (PET), for example, crosssectional images of the body may be obtained that allow the distribution of radiopharmaceuticals labelled with positron-emitting radioisotopes (e.g. 62Cu, 68Ga) to be mapped quantitatively. PET imaging allows regional tissue blood flow to be evaluated, the mapping of regional blood volume and with suitable complexes or conjugates may allow the definition of areas of receptor-specific tracer binding. Of particular interest are studies of the brain and heart (M.A. Green in 'Advances in Metals in Medicine', 1993, vol. 1, pp. 75-114, Jai Press, New York). Imaging agents for the brain and heart based on 99mTc are also particularly important in single proton emission computer tomographic (SPECT) techniques.

Examples in use include Tc(V)-HMPAO (hexamethyl-propyleneamine oxime) and Tc(V) ECD (ethylcysteinate dimer) both of which are relatively lipophilic, charge neutral complexes that can penetrate the blood-brain barrier in humans. Both have some drawbacks: the Tc-HMPAO complex is unstable in vitro and needs to be injected 30 minutes before use and both complexes exhibit competitive soft-tissue uptake in the facial area (T.R. Carroll, in 'Advances in Metals in Medicine, vol. 1, pp. 1-24, Jai Press, 1993, eds. B.A. Murder and M.J.

Abrams).

We now report a new class of compounds, amenable to control of complex lipophilicity, based on aza-methylenenthiophosphinic acids. This class of N2S2 ligands form well-defined 1:1 complexes with metal species such as zinc(II), copper(II), Tc03+ and ReO3+, that may allow their use in radiolabelled complexes for SPECT or PET imaging for example with 99mTc, 62Cu or 64cut Summary of the Invention Thus, according to one aspect of the present invention, we provide a compound of general formula (1)

wherein Alkl is a C14 alkylene, cycloaliphatic or oxoalkyl chain, optionally substituted by one or more aryl or optionally substituted C1.6 alkyl groups; and R1 and R2 which may be the same or different is each a hydrogen atom or an optionally substituted straight or branched C1 6 alkyl group; q is zero or an integer 1 or 2; R3 and R4 which may be the same or different is each an alkyl, alkoxyalkyl or aryl group each of which may be optionally substituted by alkyl, alkoxyalkyl, aryl, halide, CN, N02, SO3H, CO2R1. NH2 or substituted amino groups; X and Y which may be the same or different are either 0 or S as long as one is S; and metal complexes and/or salts thereof.

In the compounds of formula (1), R1 and R2 may be, for example, H or Me. The linking chain, Alkl, may be, for example, ethylene or propylene, optionally substituted at any carbon with a C1 3 alkyl or alkoxyalkyl group. Compounds in which q is 1 are preferred, in particular when Alkl is an optionally substituted ethylene or propylene chain.

In the compounds of formula (1), it will be appreciated that the nature of the substituents R3 and R4 may be varied widely without substantially affecting the donor properties of the compound as a ligand for the complexation of metal ions. Thus R3 and R4 may be any suitable organic radical and may, in principle, serve as a linkage point to a targeting vector such as a peptide, hormone, protein, carbohydrate or oligonucleotide. Thus, for example, R3 and R4 may be methyl ethyl or phenyl and compounds where R3 is the same as R4 are particularly preferred.

In the compounds of formula (1), X and Y may both be sulfur, or one may be sulfur and one oxygen. Compounds in which X is S and Y is 0 are particularly preferred.

Metal complexes of the compounds of formula (1) include complexes wherein the metal is dipositive, including Cu, Mn, or where the metal forms well-defined oxo complexes including technetium and rhenium. In general, the metal is preferably a radioisotope. 62Cu and 64Cu are preferred and 99mTc is particularly preferred. Salts of the compounds of formula (1) include salts with bases e.g. protium, sodium and potassium salts, or acid addition salts such as hydrochlorides, pharmaceutically acceptable salts are particularly preferred.

The following examples illustrate the preparation of compounds for use according to the invention. The precursor amino-acids were prepared as described by G.B. Bates, E. Cole et al (J. Chem. Soc., Dalton Trans., 1996, 2693).

Example 1 - Preparation of Ethylenediiminodimethylenebis(phenylthiophosphinic acid) (a) N,N' p-Toluenesulphonyl N,N' bis(Methylene [Phenylphosphinic] Acid) 1,2 Diaminoethane The amino-acid, ethylenediiminodimethylenebisphenylphosphinic)acid (5.7g. 14.1 mmol) was stirred in water (30ml) and sodium hydroxide was added until the solids dissolved at pH 10. p-Toluenesulfonyl chloride (5.9lg, 3lmmol) was added as a solid and the reaction mixture heated to 40"C for 36h, maintaining a basic pH by further addition of sodium hydroxide. The small excess of tosyl chloride was removed by filtration upon completion of the reaction. A fine solid was precipitated by addition of hydrochloric acid (pH2) and the remaining liquor was decanted after centrifugation.

The solid was recrystallised from boiling water and a few drops of concentrated hydrochloric acid, then filtered and dried to give a white solid (6.5g, 65%) m.p. 295-6 (decomp.) 31p NMR (101.26MHz, D20, pD14) bp 27.7; 1H NMR (250.13 MHz, D,O, pD14) H 1.65 (6H, s, -CH?), 2.35 (4H, s, NCH2CH2N), 2.88 (4H, d, J=2.3Hz, J=7. 1Hz, PCH2N). 6.55 (4H, d, J=8Hz, TsH), 6.77 (4H, d, J=8Hz, TsH), 6.86 (6H, m, Ph), 7.13 (4H, m, Ph); 13C NMR (62.9MHz, D20, pD14) 8c 20.56, (s, -CH3). 45.33 (s, NCH,CH2N), 47.87 (d, J=109Hz, NCH2P), 126.78 (s, Ts), 128.10 (d, 3J=12Hz, Ph), 129.52 (s, Ts) 130.64 (d, 2J=8.7Hz, Ar), 131.11 (s, Ar), 134.65 (d, 1Jp=123Hz), 144(s, S(0)2-C); m/z (ESMS-, MeOH) 674.9 (100%, M-2H+); i.r. 3423 (br), 2360, 1620 (br) 1345, 1160, 1129, 1043, 823, 739, 698, 625, 549, 525; (b) N,N' bis p-Toluenesulfonyl N,N' bis(Methylene Phenylthiophosphinic chloride) 1,2-diaminoethane The ditosylamide prepared above (2.13g, 3mmol) was dissolved in dry dichloromethane (50ml) and excess oxalyl chloride (2.5ml) was added. The solution was stirred at room temperature under an inert atmosphere for 20 mins to give the acid chloride (6p 46.8 and 47.0). The solvent was removed in vacua and 2 further portions of dichloromethane (25ml) were added and then removed by evaporation under reduced pressure to remove any traces of oxalyl chloride. The crystalline solid was dried thoroughly in vacuo.

Excess thiophosphorylchlolide (40ml) was added to the solid with a drop of DMF and the reaction mixture was stirred at 110 C overnight. The solvent was removed in vacua and 3 portions of dichloromethane (Sml) were added and then removed by evaporation under reduced pressure to remove any volatile material to give a yellow crystalline solid (2.2g, 94%), m.p.70oC; 31p NMR (101.26 MHz, CDCl3) 8p 79.8, 80.2; 1H NMR (250.13 MHz, CDCl3) 8H 2.42 (6H, s, Ts-Ch3) 3.63 (4H, m, NCH?CH2N), 4.21 (2H, dd, Jp=18.3Hz, PCR?N), 4.46 (2H, dd, JAg=15Hz PCH2N), 7.26 (4H, d+d, o-PhH) 7.60 (10H, m, aromatic), 8.0 (4H, d+d, aromatic); (c) N,N' bis p-Toluenesulfonyl N,N' bis(Methylene[Phenylthiophosphinic]Acid)- 1,2- di aminoeth ane.

The acid chloride prepared above (3g) was heated under reflux in a solution of potassium hydroxide (50ml) for 12h. The mixture was acidified to pH2 with 4M hydrochloric acid and the aqueous phase was decanted leaving an extremely viscous residue. This was washed with water (2 x 20ml) and dried to give a yellow, crystalline solid in quantitative yield; 31P NMR (101.26 MHz, CDCl3) bp, 58.26.

(d) Ethylenediimi nodi methylenebis(phenylthiophosphinic acid).

The ditosylamide prepared above (1.065g, 1.5mmol) was added portionwise to a solution of phenol (1.4g, 15mmol) in 45% HBr in glacial acetic acid (30ml). The mixture was stirred at 40 C for 4 days and the resulting precipitate was separated from the liquor. The solid was washed with potions of ether (4 x 35ml) to remove the remaining phenol and dried to give a pale yellow solid (650mg, 77%; 31p NMR (101.26 MHz, D20, pD14) 6p 62.7; 1H NMR (250.13 MHz, D20, pD) 8H 2.09 (4H, s, NCH2CH2N), 2.96 (4H, dd, 2J=l2Hz, 2JHAHB=5.9Hz, PCHN), 7.49 (6H, m, m-, p ArH), 7.74-7.82 (4H, m, o-ArH); 13C NMR (62.9 MHz, D20, pD14) SC 50.98 (d, 3Jp=9.7Hz, NCH2CH2N), 57.52 (d, Jp=77Hz, NCH2P), 131.17 (d, 2J=llHz, o-Ar), 133.04 (d, 3J=9Hz, m-Ar), 133.87 (s, mAr), 141.09 (d, 1Jp=96. P-Ar), m/z (ESIMS-) 421(100%, M-2H+ + Na+); elemental analysis found C, 33.92; H, 4.24%; N, 4.81; C16H22N2o2P2S2 2HBr requires C, 34.18; H, 4.30; N, 4.98%.

Example 2 - Preparation of trimethylenediiminodimethylenebis(phenylthiophosl)hinic acid, (a) N,N' bis p-toluenesulfonyl-N,N' bis(Methylene[Phenylphosphinic])Acid 1,3 propanediamine The amino-acid trimethylenediiminodimethylenebis(phenylphosphinic acid) (2.3g, 5.5mmol) was stirred in water (looms) and sodium hydroxide was added until the reaction mixture was a solution at pH 10. p-Toluenesulfonyl chloride (1.86g, 12mmol) was added as a solid and the reaction mixture heated to 40C for 4 days, maintaining a pH of 10 by further addition of sodium hydroxide. The excess tosyl chloride was removed by filtration.

A fine solid was precipitated by addition of hydrochloric acid to pH 2.5, which was removed by filtration and dried to give a white solid (2.3g, 58%) m.p. 190-2"C; 31p NMR (101.26 MHz, D20, pD14) 8p 25.3; 1H NMR (250.13 MHz, D2O, pD14) SH 1.03 (2H, m, NCH2CHzCH2N) 2.35 (6H, s, -CQ), 2.50 (4H, t, NCH2CH2CHoN), 3.20 (4H, d, Jp=8.7Hz, PCHoN), 7.27 (8H, dd, J=8.3Hz, TsH), 7.47-7.66 (1or, m, Ph); 13C NMR (62.9 MHz, D20, pD14) EC 23.41 (s, NCH2 H2CH2N), 25.15 (s, -CH3), 47.60 (s, NH2CHH2N), 49.09 (d, Jp=107Hz, NCH2P), 129.47 (s, Ts), 131.19 (d, 3J=12Hz, Ph), 132.78 (s, Ts) 134.06 (d, 2J=9.6Hz, Ar), 137.69.(d, 1Jp=128.6Hz, Ar), 147.65.(s, S(0)2-C); i.r. 3447, 3059, 2955, 2923, 2251, 1597, 1494, 1439, 1157, 1089, 962, 816, 738,694,652, 549, 518cm-1: elemental analysis found C, 52.65; H, 5.23%; N, 3.80; C31H36N2O8P2S2.H2O requires C, 52.53; H, 5.40; N, 3.95%.

The subsequent transformations used to convert this N-tosyl amino-acid into the desired product were effected as shown in example 1, giving in turn the phosphinic acid chloride (8p 47.4 (CH2Cl2)), the thiophosphinic acid chloride (8p 75.0 (CDCl3)), the thiophosphinic acid (6p 54.4 (pD12)) and finally detosylation yielded the amino-thiophosphinic acid (6p 74.0 (D20)); ESMS (MeOH): 436.4 (M+Na)+.

Example 3 - Preparation of ethylenediiminodimethylenebis(methylthiophosphinic acid) (a) N,N' bis (p-toluenesulfonyl) N,N' bis (Methylene[Methylphosphinic]) Acid 1,2 diaminoethane The amino acid ethylenediiminodimethylenebis(methylphosphinic acid) (2.44n, 10 mmol) was dissolved in water ( 30ml) and sodium hydroxide was added to pH 10. p Toluenesulfonyl chloride (3.43g, 22 mmol) was added as a solid and the reaction mixture heated to 40"C for 4 days, maintaining pH 10 by further addition of sodium hydroxide. The excess tosyl chloride was removed by filtration. The solution was acidified with hydrochloric acid to pH 0.5 and the solvent removed in vacuo to give a colourless solid which was washed with sparing amount of cold water to remove the salts and p toluenesulfonic acid. It was dried to give a white solid (3.3g, 60%); 31p NMR (101.26 MHz, CDCl3) 8p 47.74; 1H NMR (250.13 MHz, CDCl3) 8H 1.51 (6H, d, Jp=9.6Hz, P CH3) 2.46 (6H, s, Ts-CH3), 3.43 (4H, d, Jp=9.6Hz, PCH?N), 3.48 (4H, s, NCH2CH?N), 7.36 (4H, d, JAB=8.2Hz, TsH), 7.72 (4H, d, JAg=8.1Hz, TsH); The subsequent transformations used to convert this N-tosyl amino-acid into the desired product were effected as shown in example 1, giving in turn the phosphinic acid chloride (bl) 60.2 (CH2Cl2)), the thiophosphinic acid chloride (6p 87, CDCl3), the thiophosphinic acid (8p 75.1, pD12) and finally detosylation yielded the amino-thiophosphinic acid (#p 84, pD10).

The following example illustrates the formation of a metal complex of the amino-thiophosphinic acid ligands: Example 4 - Preparation of the rhenium(V)-mono-oxo complex of ethylenediiminodimethylenebis(phenylthiophosphinic acid).

To a solution of ReOCl3 (PPh3)2 (83mg, O.lmmol) in distilled benzene (25cm3) was added a solution of ethylenediiminodimethylenebis(phenylthiophosphinic acid) (40mg, O.lmmol) and the solution was heated under reflux for 30h. The solution became a deep claret-red and after removal of the solvent under reduced pressure, the residue was washed with benzene (3 x 10cm3) and diethyl ether (3 x 10cm3) and then dried in vacllo to give a dark red solid (5()mgs). ESMS (MeOH, negative ion): 597.1, 599.1 (LReO-3H)- with good agreement between experimental and theoretical isotope patterns.

Related mono-oxo technetium(V) complexes of this ligand may be prepared in aqueous solution from 99'nTc04- in the presence of an excess of the ligand and with added sodium dithionite, stannous chloride or a similar suitable reducing agent.

Claims (4)

Claims

1. A compound of formula (1)

wherein AIkl is a C14 alkylene cycloaliphatic or oxoalkyl chain optionally substituted by one or more aryl or optionally substituted C1-6 alkyl groups; and R1 and R2 which may be the same or different is each a hydrogen atom or an optionally substituted straight or branched C1 6 alkyl group; q is zero or an integer 1 or 2; R3 and R4 which may be the same or different is each an alkyl, alkoxyalkyl or aryl group each of which may be optionally substituted by alkyl, alkoxyalkyl, aryl, halide, cyano, N02, S03H, CO2H, C02R1, NH2, or NR1R2 groups; X and Y which may be the same or different are either 0 or S as long as one is S; and metal complexes and/or salts thereof.

2. A metal complex of a compound of formula (1) of a salt thereof for use as an imaging agent in radioisotope-based tomography.

3. A metal complex of a compound of formula (1) or a salt thereof for use as an imaging agent as claimed in claim 2 wherein X=O, Y=S and R1 and R2 are alkyl, substituted alkyl, alkoxyalkyl or optionally substituted aryl group.

3. A metal complex of a compound of formula (1) or a salt thereof for use as an imaging agent as claimed in claims 1 and 2 wherein the metal is any isotope of copper or technetium.

4. A metal complex of a compound of formula (1) or a salt thereof for use as an imaging agent as claimed in any of the preceding claims wherein q is 1, R1=R2=H or Me and Alkl is (CH2)n where n=2, 3 or

4.

5. A metal complex of a compound of formula (1) or a salt thereof for use as an imaging agent as claimed in claim 4 wherein Z is oxygen, Y is sulfur and R4 is an alkyl, substituted alkyl, alkoxyalkyl or optionally substituted aryl group.

6. A composition comprising a compound of formula (1), as defined in claim 1, or a metal complex and/or salt thereof together with one or more pharmaceutically acceptable carriers.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS Claims 1. A compound of formula (1)

wherein n = 2 or 3; q is zero or an integer 1 or 2; R1 and R2 which may be the same or different is each an alkyl, alkoxyalkyl, or aryl group each of which may be optionally substituted by alkyl, alkoxyalkyl aryl, halide, cyano, NO2, SO3H, CO2H, C02R, NH2 or substituted amino groups; X and Y which may be the same or different are either 0 or S, as long as one is S; and metal complexes and/or salts thereof.

9. A metal complex of a compound of formula (1) of a salt thereof for use as an imaging agent wherein q = 1, and n = 2 or 3.