Five-coordinate aminophosphine platinum(II) complexes containing cysteine derivatives as ligands

The platinum(II) complex, [Pt(NP3)Cl]Cl (1) [NP3=N(CH2CH2PPh2)3] reacts with thiol-containing biomolecules such as N-acetyl-l-cysteine (N-Ac-l-CysH) and the tripeptide reduced glutathione (γ-l-Glu-l-Cys-Gly, GSH) to afford the intensely-coloured five-coordinate complexes, [Pt(NP3)(N-Ac-l-Cys-S)] (2) and [Pt(NP3)(GS-S)] (3), respectively. Complex 2 was shown by X-ray crystallography to be trigonal bipyramidal and contained an axial PtS bond trans to N, the first example of such a complex. Coordination to Pt(II) protected the thiol from oxidation: reactions of complexes 2 and 3 with H2O2 gave the four-coordinate complexes [Pt(NP(O)P2)(SR-S)] (4, SR=N-Ac-l-Cys; 5, SR=GS) which possess a dangling arm phosphine oxide group. The thiolate adducts 2 and 3 exhibited low toxicity to cells.