Determination of enantiomers of histidine, arginine and other amino acids by HPLC of their diastereomeric N-ethoxycarbonyldipeptides.

Oxazolones and symmetrical anhydrides react efficiently with amino acids if the aqueous solvent includes a high proportion of dimethylformamide, the temperature is not lowered and sodium carbonate is used for neutralizing the amino acids. Subsequent separation of the diastereomeric products by high-performance liquid chromatography on a C-18 column provides a simple method for determining enantiomers. The symmetrical anhydrides of N-ethoxycarbonylvaline and phenyl-alanine are reagents suitable for determining enantiomers. Enantiomers of arginine and histidine in a mixture of amino acids can be determined if the products of the reaction are first fractionated by a simple extraction.