Stereoselectivity in reactions of metal complexes VIII . Asymmetric synthesis of some amino acids by stereoselective transamination of aliphatic keto acids in mixed ligand copper(II)‐ Schiff ‐base complexes

Optically active alanine, valine and leucine were obtained by a transamination reaction between pyridoxamine and the corresponding α‐keto acid in the presence of a Cu 2+ ‐complex with the tridentate ligand 2,6‐bis[(3 S )‐3‐phenykl‐2‐azabutyl]pyridine. In each case the amino acid with ( R )‐configuration was formed preferentially, and the maximum enantiomeric excesses were 54% (alanine), 48% (leucine) and 29% (valine). The stereoselectivity of the reaction is discussed in terms of the possible structure and the stability of the intermediate Cu 2+ ‐ketimine‐ligand complex.