Enantioselectivity of 6-O-alkyldimethylsilyl-2,3-di-O-methyl-beta-cyclodextrins as chiral stationary phases in capillary GC

Three new 2,3-di-O-methyl-beta-cyclodextrins having different 6-O-alkyldimethylsilyl groups, 6-O-isopropyldimethylsilyl-2,3-di-O-methyl-beta-cyclodextrin (IPDM-beta-CD), 6-O-thexyldimethylsilyl-2,3-di-O-methyl-beta-cyclo-dextrin (TXDM-beta-CD) and 6-O-cyclohexyldimethylsilyl-2,3-di-O-methyl-beta-cyclodextrin (CHDM-beta-CD), have been prepared and their enantioselectivities for the separation of a range of test racemic compounds in capillary gas chromatography investigated. IPDM-beta-CD gave good separations of all of the test compounds studied while TXDM-beta-CD showed the highest enantioselectivity for the test compounds except for three nonpolar compounds. CHDM-beta-CD showed very low enantioselectivity. Differences in enantioselectivities among the CD derivatives were rationalized in terms of the steric hindrance and hydrophobicity effects influencing the inclusion of the guest in the host CD derivatives.