Enantioseparation of Amino Acid Derivatives with a Cellulose-Based Chiral Stationary Phase

Five structurally related amino acid derivatives were enantioseparated by HPLC with a commercially available chiral stationary phase, Chiralcel OD-H. The chromatographic experiments were performed in the normal phase mode. n-Hexane/polar alcohol was used as mobile phase. Excellent baseline enantioseparations could be obtained for all these solutes. The effects of the concentration of polar alcohol and the column temperature on the retentions and enantioseparations were studied in detail. From the van't Hoff plots the corresponding apparent thermodynamic parameters were derived. Mechanism aspects of chiral recognition were discussed based on the relationship between the thermodynamic parameters and the structures of the solutes. It was found that the substituent of the phenyl group on the residual group of the amino acid derivatives was close relevant to thermodynamic origin of enantioseparation. Much better enthalpy–entropy compensation effect was obtained by plotting the differential, rather than the original, thermodynamic parameters.