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

Dependence of the retention factor of the first-eluting enantiomer (k1) of 2-naphthol-substituted glycine ester (methyl, ethyl, propyl, 2-propyl) derivatives 2–5 (A) and of 1-naphthol-substituted glycine ester derivatives 6–10 (B) on the Meyer substituent parameter (Va). Columns, Cellulose-1, Cellulose-2, Cellulose-3, Cellulose-4 and Amylose-2. [Display omitted] ► Separation of glycine ester analogs on polysaccharide-based CSPs. ► Structure–retention relationships of separation based on size-descriptor (Meyer) parameters. ► Thermodynamics of separation of glycine ester analogs. ► Entropically controlled chiral separation. 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°C. Thermodynamic parameters were calculated from plots of lnk or lnα vs. 1/T. Δ(ΔH°) ranged from −10.1 to 6.2kJmol−1, Δ(ΔS°) from −31.5 to 22.5Jmol−1K−1 and −Δ(ΔG°) from 0.4 to 1.4kJmol−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.