S-alkyl and S-alkylaryl cysteine complexes with platinum(II) and their interactions with nucleosides

Abstract

The reactions of K 2PtCl 4 with the aminoacids, S-methyl-L-cysteine, S-ethyl-L-cysteine, S-benzyl-L-cysteine, S-para-nitro-benzyl-L-cysteine, S-diphenyl-methyl-L-cysteine, S-tribenzyl-L-cysteine and S-4′,4′-dimethoxy-diphenylmethyl-L-cysteine were studied in neutral or acidic aqueous solutions. Complexes of the formulae PtLCl 2, [PtL 2]Cl 2 and Pt(L-H +) 2, where L = aminoacid, were isolated in the solid state and their structures investigated with elemental analysis, conductivity measurements, IR, 1H NMR and 13CNMR spectra. The results show that the coordination sites of Pt(II) with the amino-acids are the N and S atoms, producing two diastereoisomers around the chiral sulphur atom, which were identified in the 1H NMR and 13CNMR spectra. The complexes PtLCl 2 further react with the nucleosides guanosine and inosine. The complexes [PtL(nucl) 2]Cl 2 were isolated from these reactions and studied with the same methods. They showed a PtN 7 bonding with the nucleosides and retained the N, S bondings with the aminoacids. As a result of the higher trans influence of S than N, the nucleoside molecule coordinated to the metal through N 7 and trans to S has a weaker bond strength than the other, as it is revealed from the 1H NMR and 13C NMR spectra of these complexes.