Direct chiral separation of unnatural amino acids by high-performance liquid chromatography on a ristocetin a-bonded stationary phase

Direct high-performance liquid chromatographic chiral separation of numerous underivatized unnatural amino acids on a ristocetin A-bonded chiral stationary phase used in the reversed-phase and in the polar organic chromatographic modes is reported. The effects of different parameters such as mobile phase composition, temperature, and the structure of the analytes on the selectivity in both chromatographic modes are discussed. By variation of the parameters, the separation of the stereoisomers was optimized and, as a result, baseline resolution was achieved in most cases.