Enantiomeric separation of phenoxy acid methyl esters by gas chromatography using 2,3,-di-O-methyl-6-0-tert-butyldimethylsilyl derivatives of alpha- and gamma-cyclodextrins as stationary phases

Abstract

Enantiomeric separation of forty-six phenoxy acid methyl esters were studied by means of capillary gas chromatography using hexakis (2,3-di-O-methyl-6-O-tert-butyldimethylsilyl) cyclomaltohexaose (or ASiMe) and octakis (2,3-di-O-methyl-6-O-tert-butylimethylsilyl) cyclomaltooctaose (or GSiMe) mixed in polysiloxane as chiral stationary phases. The effects of type, position and number of aromatic substitution on the retention and enantioselectivity were systematically investigated. Thermodynamic data were also calculated to clarify the strength of analyte-stationary phase interaction and enatioseparation towards the selected group of phenoxy acid methyl esters. While GSiMe could enantioseparate only 17 analytes, smaller-sized ASiMe could resolve enantiomers of 32 analytes with higher degree of separation than GSiMe. It was found that the type and position of substituent on the aromatic ring played an important role on enantioseparation. For most cases, substitution at meta-position of the aromatic ring seems to enhance the enantiorecognition. Among all tested analytes, methyl 2-(3’, 5’-dichlorophenoxy) propanoate (3,5C1) shows the highest degree of enantioseparation on ASiMe column.