Competitive reactions of L-methionine and 5'-GMP towards platinum (II) complexes

The complex-formation reactions of the platinum(II) complexes, Pt(dien)H2O]2+, PtCl(dien)]+ and PtBr(dien)]+ (dien is diethylenetriamine) with some biologically relevant ligands such as inosine (INO), inosine-5'-monophosphate (5'-IMP), guanosine-5'-monophosphate (5'-GMP), glutathione (GSH) and L-methionine (S-meth), were studied by UV-Vis (UV-Visible) spectrophotometry and 1H NMR spectroscopy. Reactions of the PtCl(dien)]+ with L-methionine were studied in the presence and absence of 5'-GMP. The rate constants clearly showed a kinetic preference toward L-methionine. However, competitive reactions of PtCl(dien)]+ with L-methionine and 5'-GMP demonstrated initially rapid formation of Pt(dien)(S-meth)]2+ followed by displacement of L-methionine by 5'-GMP. In the later stages the concentration of Pt(dien)(N7-GMP )]2+ is predominant. The results are analyzed in reference to the anti-tumour activity of Pt(II) complexes.