FREE-SOLUTION CAPILLARY ELECTROPHORETIC RESOLUTION OF CHIRAL AMINO-ACIDS VIA DERIVATIZATION WITH HOMOCHIRAL ISOTHIOCYANATES .1.

Within the framework of a more general study aimed at the enantiomeric resolution of non-UV-absorbing chiral amino acids via derivatization with chiral isothiocyanates, we have examined the applicability of two such derivatizing agents, (S)-1-(1-naphthyl)ethyl isothiocyanate (SNEIT) and (S)-1-phenylethyl isothiocyanate (SAMBI), to the resolution of the enantiomers of alanine, phenylalanine, and valine in free-solution capillary electrophoresis (FSCE). Isothiocyanates have distinct advantages as chiral derivatizing agents in enantiospecific chromatographic analysis, and the two reagents were readily synthesized from commercially available reagents. SNEIT, previously not fully described in the literature, was characterized by rigorous physicochemical and spectroscopic means. The two diastereoisomeric thiourea derivatives of each amino acid were separated by FSCE. Heptakis-2,3,6-tri-O-methyl-beta-cyclodextrin was effective in assuring the solubility of the derivatives in the working buffer and was more efficient than beta-cyclodextrin in both dissolving the thioureas and improving the electrophoretic resolution. Enantiomeric pairs migrated in the order L before D. Under the conditions used SAMBI-derivatized amino acids had longer elution times than the corresponding SNEIT derivatives. The diastereomeric derivatives of valine and of phenylalanine had larger separation factors alpha than the corresponding SAMBI derivatives, while the derivatives of alanine had nearly identical alpha values with the two derivatizing agents. The two reagents may be advantageous in the enantiospecific analysis of amino acids, and it appears that further exploration of these and other similar reagents is warranted.