Cisplatin analogues with sulfur donor ligands. (Ethylenediamine)platinum(II) complexes with ligands possessing a sulfinyl or sulfanyl group linked to an anionic oxygen donor atom. Reactivity and cytotoxicity

Complexes of formula [Pt(en)L]NO₃, where en = ethylenediamine and L is a ligand in which a methylsulfinyl or methylsulfanyl group is linked to a carboxylate or phenolate moiety, have been synthesized and characterized by spectroscopic techniques. The ligand L is chelated to Pt via the sulfur and anionic oxygen atoms. The reactivities of these complexes towards nucleophiles [Nu = Cl^- or guanosine 5′-monophosphate(2-), GMP] have been investigated by ¹H NMR spectroscopy; GMP is more reactive than Cl^-. The Pt-O bonds react more readily than the Pt-S bonds and, depending on the nature of L and Nu, the reactions either stop at the monosubstituted complex [Pt(en)L(Nu)] (with L monodentate and co-ordinated to Pt via the sulfur atom), or yield [Pt(en)(Nu)₂]. The complex with L = 2-(methylsulfanyl)phenolate is unreactive. The stable monosubstituted products have been characterized. There is little correlation between the rates and the modes of reactivity of complexes [Pt(en)L]NO₃ towards GMP and their cytotoxicities against the human ovarian carcinoma A2780 cell line.