The anticancer drug cisplatin results in cell death due primarily to its interaction with DNA, specifically at guanine residues. The interaction of cisplatin and its analogs with proteins is a side reaction that could be responsible for toxicity and/or acquired resistance of the drug. Also, platinum complexes may be useful as agents that cleave proteins and peptides regioselectively on the C-terminal side of methionine. We are therefore characterizing the reaction of N-acetyl methionine, with bulky platinum complexes such as [Pt(Me₄ en)(D₂O)₂]²⁺ (Me₄en = N,N,N',N'-tetramethylethylenediamine) and [Pt(Et₂en)(D₂O)₂]²⁺ (Et₂en = N,N-diethylethylenediamine); the latter is non-C₂-symmetrical and has bulk at only one nitrogen. Although several types of coordination environments are possible, our NMR data are consistent with the formation of chelates in which one N-acetylmethionine coordinates to the platinum via sulfur and oxygen atoms. Furthermore, the dominant product appears to have the sulfur atom trans to the nitrogen containing the ethyl groups.