REACTIONS OF THE CIS-DIAMMINEDIAQUAPLATINUM(II) CATION WITH GLYCINAMIDE, N-GLYCYLGLYCINE, AND N-(N-GLYCYLGLYCYL)GLYCINE - CRYSTAL-STRUCTURE OF A COMPLEX WITH 2 DIAMMINEPLATINUM(II) CATIONS BOUND TO GLYCYLGLYCINATE

Multinuclear (15N, l95Pt, 1H, 13C) NMR spectroscopy has been used to study the reactions of c/í-Pt(NH3)2(H20)22+ with glycinamide (glyamH),/V-glycylglycine (diglyH2), and JV-(,/V-glycylglycyl)glycine (triglyH3). With glycinamide near pH 5 a N,O-chelate complex is formed, Pt(NH3)2(glyamH-A;0)2+. Addition of alkali in an attempt to form a N,N’-chelate with deprotonated ligand caused rapid hydrolysis to Pt(NH3)2(gly-yv,0)+ and NH3 (glyH = glycine). With glycylglycine (diglyH2), the initial complex formed was m-Pt(NH3)2(diglyH2-0)(H20)2+, in which the ligand is bound only through the carboxyl oxygen. When the solution was allowed to stand near pH 5, a new complex formed, [|Pt(NH3)2)2(digly)]2+, in which one platinum atom is bound to the ligand through terminal oxygen and peptide nitrogen and the second platinum atom is chelated by the peptide oxygen and terminal nitrogen. The crystal structure of the sulfate salt has been determined and confirms this stoichiometry. Crystals of [|Pt(NH3)2|2(digly)](S04)’1.35H20 are triclinic, space group P\, with a = 6.157 (2) Å, b = 9.248 (4) Å, c = 14.550 (7) Å, a = 105.78 (2)°, β = 91.79 (2)°, γ = 105.51 (2)°, and Z = 2. With excess glycylglycine near pH 4, NMR peaks due to the complex in which terminal carboxylate and peptide nitrogen chelate to diammineplatinum were observed. In strongly acidic solution (pH ‹l), this complex converts to the other N,O-chelate complex in which terminal nitrogen and peptide oxygen chelate. The peptide bond in the latter complex slowly hydrolyzes in acid, to give Pt(NH3)2(gly-Ar,0)+. With triglyH3, there was formation initially of í’/j-Pt(NH3)2(triglyH3-0)(H20):+ and subsequently of [|Pt(NH3)2)3(trigly)]3+, with three Pt atoms bound through N,O-chelate rings. © 1990, American Chemical Society. All rights reserved.