Asymmetric synthesis of amino acids by Cr(II) complexes of natural amino acids

Stoichiometric reduction of the C,N double bond of oxime precursors of a-amino acids was performed in aqueous media by Cr(II) complexes of natural amino acids. The reduction of oximes of alpha-ketophenylacetic, alpha-keto-beta-phenylpropionic and alpha-ketopropionic acids proceeded up to > 90% conversion and 2-30% enantiomeric excess. 1:2 complexes of Cr(II) with L-alanine, L-valine, L-aspartic acid, L-histidine and L-phenylalanine were used as reducing agents. The reduction of alpha-(oximino)phenyl acetic acid showed increasing e.e. (and decreasing conversion) with increasing temperature.