Determination of the enantiomers of α-amino acids and α-amino acid amides by high-performance liquid chromatography with a chiral mobile phase

Abstract

A high-performance liquid chromatographic method for the enantiomeric analysis of a mixture of an α-amino acid and the corresponding acid amide is described. Reversed-phase chromatography with copper(II) acetate and N,N-di- n-propyl- l-alanine in the mobile phase are used for the separation. For Val and Val-NH 2, several parameters affecting retention and enantioselectivity were investigated. The results indicate that by manipulation of pH, ionic strength, temperature, concentration of Cu II, N,N-di- n-propyl- l-alanine and ion-pairing reagent, good control of enantiomeric separation can be achieved. For α-amino acid amides a mechanism is proposed which may account for the retention and enantioselectivity. Examples of enantiomeric analysis of mixtures of α-amino acids and α-amino acid amides with aliphatic, aromatic and polar side-chains are given. The method can be used for the control of the enantiometric purity of α-amino acids and the corresponding acid amides obtained by enantioselective synthesis.