Development of the high-performance liquid chromatographic method for the enantioseparation of unusual glycine ester analogs on polysaccharide-based chiral stationary phases

The stereoisomers of ten unusual amino acid analogs, 1- and 2-naphthol-substituted glycine and its ester derivatives, were separated on chiral stationary phases containing the chiral selectors cellulose tris-(3,5-dimethylphenylcarbamate) (Cellulose-1), cellulose tris-(3-chloro-4-methylphenylcarbamate) (Cellulose-2), cellulose tris-(4-methylbenzoate) (Cellulose-3), cellulose tris-(4-chloro-3-methylphenylcarbamate) (Cellulose-4) and amylose tris-(5-chloro-2-methylphenylcarbamate) (Amylose-2). Experiments were performed in normal-phase mode with n-heptane/alcohol/diethylamine mobile phases in a wide temperature range: 5-50 degrees C. Thermodynamic parameters were calculated from plots of In k or In alpha vs. 1/T. Delta(Delta H degrees) ranged from -10.1 to 6.2 kJ mol(-1), Delta(Delta S degrees) from -31.5 to 22.5 J mol(-1) K-1 and -Delta(Delta G degrees) from 0.4 to 1.4 kJ mol(-1), and both enthalpy and entropy-controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. The sequence of elution of the stereoisomers was determined in some cases. (C) 2013 Elsevier B.V. All rights reserved.