The isomers of α-amino-acids with copper(II). Part 4. Catalysis of the racemization of optically active alanine by copper(II) and pyruvate in alkaline solution

Abstract

Aqueous solutions containing copper(II) ions, pyruvate, and L(+)-alanine in the molar ratio 1 : 2 : 4 give rapid racemization of alanine. The reaction is first order in the concentration of base, k_obs.=(5.43 × 10^–2)[OH^–] s^–1 at 60 °C. For the molar ratios 1 : 1 : 4 ⩽[Cu^II] : [pyruvate] : [alanine]⩽ 1 : 4 : 4 the reaction is to a very good approximation first order in the concentration of added pyruvate, k_obs.=(2.89 × 10^–4)[pyruvate] s^–1. We attribute the racemization to the involvement of Schiff-base formation. In similar systems containing Co^II, Ni^II, or Zn^II racemization is also promoted; with Cu^II the racemization of threonine and glutamic acid is also promoted.