Enantiomeric separation of phenoxy acid methyl esters by gas chromatography using derivatized beta-cyclodextrins as stationary phases

Abstract

Fourty-six phenoxy acid methyl esters were synthesized and their enantiomeric separations were studied by means of capillary gas chromatography using heptakis(2,3-di-O-methyl-6-0-tert-butyldimethylsilyl) cyclomaltoheptaose (BSiME) and heptakis (2,3-di-O-acetyl-6-0-tert- butyldimethylsilyl)cyclomaltcheptaose (BSiAC) 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 enantioseparation towards the selected group of phenoxy acid methyl esters. All tested analytes, except for 2,6Me, 2,6Cl and 2,4,6CI could successfully be enantioseparated with either BSiMe or BSiAC, or otherwise both of them. Generally, BSiME phase exhibited higher degree of enantioseparation towards most analytes than BSiAC phase. On both columns, the type, position and number of aromatic substituent strongly influence enantioseparation. Additionally, the type of substituent on cyclodextrin molecule (BSiME vs. BSiAC) affects the enantioseparation as well. Thus, both columns can be used to compliment one another to enhance the enantioseparation ability of various substituted phenoxy acid methyl esters.