Gas charomatographic enatiomeric separation of alcohols using derivatized alpha-cyclodextrin stationary phase

Abstract

Enantiomeric separations of 90 alcohols were studied by means of capillary gas chromatography using hexakis (2,3-di-O-methyl-6-O-tert-butyldimethylisilyl)cyclo-maltohexaose (or ASiMe) as chiral stationary phase. The influence of type, position and number of substituent, position of chiral center, and main-structure of alcohols, on retention and enantioselectivity was systematically investigated. Thermodynamic data and molecular docking calculation were also acquired to clarify the strength of analyte-stationary phase interaction and the mechanism of chiral recognition towards the selected groups of alcohols. The gas chromatographic results indicated that all tested analytes, except for 12,15,17, 4OMe, 4OMeBen and 2but, could be successfully enantioseparated with ASiMe. Among 90 alcohols studied, the best enantioseparation was observed on 1-(2,5-difluorophenyl)-ethanol. The effect of position of substituent towards enantioseparation was clearly seen from mono-substituted 1-phenylethanols. The enantioseparation increased as the position of substituent was in the order of para- < meta- << ortho-. Nevertheless, ortho-substituted diphenylme-thanols displayed low enantioseparation compared to 1-phenylethanols with similar substitution, demonstrating the effect of main-structure. The enantioseparation of other series of alcohols did not show a distinct trend. Results from molecular docking suggested that the orientation of complexes alcohol and ASiMe were dependable on the type, position and structure of substituent.