Enantiomeric separation off-amino acids on chemically bonded ligand exchange stationary phases

beta-Amino acid enantiomers are important pharmaceutical intermediates and generally obtained by resolution of synthetic racemates. A simple resolution method based on chiral ligand exchange chromatography with L-alpha-amino acid chemically bonded to spherical silica as the stationary phase and aqueous solution containing cupric ions as the mobile phase is described. With beta-phenylalanine and its analogous as model compounds, the effects of the silica support, chiral ligand, mobile phase composition and pH on enantiomeric separation of beta-amino acids were examined. Optimum separation conditions such as chiral stationary phase, L-hydroxyproline bonded silica (BaseLine Sil, 5 mu m); mobile phase, aqueous solution of 5 mmol/L CuSO4, pH 4.6; flow rate of 1 mL/min; detection wavelength 254 nm; column temperature and ambient were obtained. A baseline separation of the enantiomers was obtained for all 5 beta-amino acids tested (beta-phenylalanine, 3-hydroxy-beta-phenylalanine, 3-fluoro-beta-phenylalanine, 3-hydroxy- 4-methyl-beta-phenylalanine, 3,4-dimethoxy-beta-phenylalanine) with elution times less than 35 min and separation factors in the range of 1.49-1.77. Compared with similar chiral stationary phases prepared by coating silica with L-hydroxyproline derivatives, the chemically bonded phases described in the present work are advantageous in that they allow the use of organic solvents without worrying about the leach out of the chiral ligand and thus prolong the columns service life.