15N and 195Pt NMR-Study of the Effect of Chain-Length, n, on the Reactions of Amino-Acids, +NH3(CH2)NCO2 (N = 1, 2, 3), With Platinum(II) Ammine Complexes

Abstract

15N and 195Pt n.m.r. have been used to study the reactions in solution of cis -Pt(15NH3)2(H2O)22+ (1), cis -Pt(15NH3)2(OH)2 (2), cis -Pt(15NH3)2Cl2 (3), Pt(15NH3)3(H2O)2+ (4) and Pt(15NH3)3(OH)+ (5) with the amino acids +NH3(CH2)nCO2- (LH) [n = 1 ( glycine, glyH ); n = 2 (β- alanine , βalaH ), n = 3 (γ- aminobutyric acid, abaH )]. While glycine with (1) gives initially cis -Pt(NH3)2( glyH -O)(H2O)2+, with facile ring closure to Pt(NH3)2( gly - N,O)+, β- alanine and γ- aminobutyric acid with (1) give solutions containing a mixture of cis -Pt(NH3)2(LH-O)(H2O)2+, cis -Pt(NH3)2(LH.O)22+, and {Pt(NH3)2}2(μO,O-LH)(μ-OH)3+, which are quite stable kinetically under mildly acid conditions. Ring closure to Pt(NH3)2(L-N,O)+ becomes increasingly difficult as n increases. At 37°C and initial pH 7, (3) with glycine gives Pt(NH3)2( gly -N,O)+, but β- alanine and γ- aminobutyric acid give predominantly cis -Pt(NH3)2Cl(LH-O)+. Compound (4) with glycine gives initially Pt(NH3)3( glyH -O)2+, which then isomerizes to Pt(NH3)3( glyH -N)2+. In corresponding reactions with β- alanine and γ- aminobutyric acid, Pt(NH3)3(LH-O)2+ is stable indefinitely under mildly acid conditions. Differences in reactivity of the amino acids with (2) and (5) in alkaline solutions may be correlated with decreasing nucleophilicity of the amine group of NH2(CH2)nCO2- as n increases.