Synthesis of different pyrazine-bridged platinum(II) complexes and 1H NMR study of their catalytic abilities in the hydrolysis of the N-acetylated l-methionylglycine

Abstract

Four binuclear {[Pt(L)Cl]2(μ-pz)}Cl2-type complexes have been synthesized and characterized by elemental microanalyses and NMR (1H and 13C) spectroscopy (L is ethylenediamine, en; (±)-1,2-propylenediamine, 1,2-pn; isobutylenediamine, ibn; trans-(±)-1,2-diaminocyclohexane, dach and pz is bridging pyrazine ligand). The chlorido complexes were converted into the corresponding aqua species, {[Pt(L)(H2O)]2(μ-pz)}4+, and 1H NMR spectroscopy was applied to study their reactions with the N-acetylated l-methionylglycine, Ac-L-Met-Gly. The {[Pt(L)(H2O)]2(μ-pz)}4+ complex and dipeptide were reacted in 1:1 and 1:2M ratios, respectively, and all reactions were performed in the pH range 2.0–2.5 and at 37°C. In the reactions with equimolar amounts of the reactants all Pt(II) aqua complexes bind to the methionine side chain of Ac-L-Met-Gly dipeptide and promote the cleavage of the amide bond involving the carboxylic group of methionine. It was found that the amount of hydrolyzed dipeptide strongly depends from the steric bulk of bidentate coordinated diamine ligand L in {[Pt(L)(H2O)]2(μ-pz)}4+ complex (en>1,2-pn>ibn>dach). However, in the reaction with an excess of dipeptide the influence of the nature of diamine ligand L on this hydrolytic process could not be observed due to the fact that slow decomposition of {[Pt(L)(H2O)]2(μ-pz)}4+ complex was occured.