Separation of benz[ f]isoindole derivatives of amino acid and amino acid amide enantiomers on a β-cyclodextrinbonded phase

Abstract

A liquid chromatographic method for the determination of amino acid enantiomers and related amino acid amide enantiomers is presented. Fluorescent derivatives were formed by reaction with naphthalene-2,3-dicarboxaldehyde-cyanide reagent. The resulting benz[ z]isoindole amino acid enantiomers and amino acid amide enantiomers were separated on a β-cyclodextrin-bonded phase. The separations were performed with ammonium nitrate buffer containing methanol as mobile phase. The influence of methanol, pH and buffer concentration in the mobile phase on retention, enantioselectivity and resolution were examined and are discussed. Remarkable differences in retention behaviour were found for the amino acids and amino acid amides studied on changing mobile phase parameters such as buffer concentrations and pH. With this method, the separation of an amino acid, together with the corresponding amino acid amide, into their enantiomers can be achieved in a single isocratic run. The method is suitable for monitoring the enantiomeric purity of an amino acid obtained by enantioselective hydrolysis of the corresponding acid amide using an aminopeptidase.