A rapid, qualitative thin-layer chromatographic method for the separation of the enantiomers of unusual aromatic amino acids

A rapid thin-layer chromatographic (TLC) method has been developed for the separation and purity control of the enantiomers of several unusual aromati c amino acids (phenylalanine, tyrosine, histidine, and tryptophan analogs, and analogs containing tetralin or 1,2,3,4-tetrahydroisoquinoline skeletons ) synthesized in racemic or homochiral form. The compounds were analyzed on Macherey-Nagel Chiralplate TLC plates with acetonitrile-methanol-water, 4 + I + 1 or 4 + 1 + 2 (v/v) or acetonitrile-methanol-water-diisopropylethyla mine, 4 + 1 + 2 + 0.1 (v/v) as mobile phase. The compounds were visualized with ninhydrin. Good separation and reliable results were usually obtained. The configurations of the asymmetric centers of the investigated amino aci ds were determined either by use of enantiomerically pure amino acids as st andards or by use of enzymes, e.g. alpha-chymotrypsin, L-amino acid oxidase or carboxypeptidase A. By this method the configurations of unnatural amin o acids built into peptides can also be determined after hydrolysis of the peptides.