METAL-COMPLEXES OF BIOLOGICALLY IMPORTANT LIGANDS, .67. SYNTHESIS OF ALPHA-AMINO-ACIDS FROM PALLADIUM(II)-COORDINATED AND RHODIUM(III)-COORDINATED IMINES AND OXIMES OF ALPHA-OXOCARBOXYLATES

The bis-chelate complexes Pd[O2CC(R1)=NOR2]2 (1) and Pd[O2CC(R1)=NR2]2 (2, R2 optically active substituent) are synthesized by template condensation of an alpha-oxocarboxylic acid with a hydroxylamine or amine component, respectively. Similarly, the Rh(III) complexes Cp*Rh(Cl)[O2CC(R)=N(CHMePh)] (3a: R = H, 3b: R = Me) were obtained from alpha-oxocarboxylic acids and optically active 1-phenylethylamine. Catalytic hydrogenation of 1 and 2 gives directly the free alpha-amino acids with, in case of 2, ee's between 0 and 36%. Nucleophilic attack by the carbanions of RC(O)CH2CO2Et and H2NCH(CO2Et)2 at the imino carbon atom of 3a leads to the alpha-amino carboxylato complexes 4 and 5. - Compounds 4a and 5 have been characterized by X-ray diffraction. Reaction of 3a with NaBH4 or NaBD4 followed by decomposition of the complex with HCl yields N-substituted glycine and N-substituted alpha-deuterioglycine, respectively. The diastereoselectivity (70:30) of the alpha-deuteration could be determined by NMR spectroscopy.