Interaction of Platinum Agents with Amino Acids, Peptides and Proteins

4 INTERACTION OF PLATINUM AGENTS WITH AMINO ACIDS, PEPTIDES AND PROTEINS 

The reactions of cw-[Pt(NH3)2Cl(OH2)] with L-methionine under an acidic condition and at pH ss 7 have been investigated by ID Pt and N NMR as well as 2D [ H, Nj HSQC NMR [74]. When the platinum complex is in excess in an acidic solution, the initial product, cw-[Pt(NH3)2Cl(Met-S)]+ undergoes slow ring closure to cw-[Pt(NH3)2(Met-N,S)f+. Slow ammine loss occurs to produce the isomer of c -[Pt(NH3)Cl(Met-N,S)]+ with chloride trans to sulfur. When methionine is in excess, a reaction sequence is proposed in which tra 5 -[Pt(NH3)Cl(Met-S)2]+ isomerizes to the cis isomer, with subsequent ring closure reactions leading to the formation of cw-[Pt(Met-N,S)2] +. In contrast to methionine which is unreactive toward cw-[Pt(NH3)2Cl(OH)] at pH 7, 

L-cysteine reacts readily with c -[Pt(NH3)2Cl(OH)], giving various reaction products including bridged species. 

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