Direct and indirect high-performance liquid chromatographic enantioseparation of β-amino acids

Direct and indirect reversed-phase (RP) high-performance liquid chromatographic methods were developed for the separation of enantiomers of 18 unnatural β-amino acids, including several β-3-homo amino acids. The direct separations of the underivatized analytes were performed on chiral stationary phases (CSPs) containing macrocyclic glycopeptide antibiotic teicoplanin (Chirobiotic T column) and teicoplanin aglycone (Chirobiotic TAG column). The indirect method involved pre-column derivatization with a new chiral derivatizing agent (CDA), (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester ((S)-NIFE), and subsequent separation of diastereomers on Discovery C18 and Hyperpep 300 C18 columns. The different methods were compared in systematic chromatographic examinations. The effects of organic modifier, mobile phase composition, pH and flow rate on the separation were investigated.