Peptide formation in the presence of metal ion protecting groups: II. Determination of the optical purity of amino acids and peptides bound to pentaamine cobalt (III)

A quantitative study of the degree of racemization induced by the [(NH3)5Co-(III)-] protecting group when bound to the C-terminal of the amino acids Leu, Phe, and His, as has been carried out. Racemization was determined by forming the diastereomeric cobalt dipeptides [(Leu)(AA)Co(III)(NH3)5] where AA = L-Leu, L-Phe, and L-His; after cobalt removal (using NaBH4), the peptide diastereomers were analyzed quantitatively using an amino acid analyzer. No racemization was observed within experimental error (0.3%) as a result of the substitution of the [(NH3)5Co(III)-] group on the amino acids and peptides studied.