ENANTIOMER SEPARATIONS BY CAPILLARY GC ON MODIFIED CYCLODEXTRINS

Three new chiral selectors, butyldimethylsilyl-2,3-diethyl-alpha-cyclo dextrin, 6-tert-butyldimethylsilyl-2,3-diethyl- and dipropyl-beta-cycl odextrin (TBDE-alpha-CD, TBDE-beta-CD, TBDP-beta-CD) were synthesized and tested as chiral stationary phases in capillary gas chromatography . TBDE-beta-CD in particular showed a high enantioselectivity for test chiral compounds due to good solubility in a polar polysiloxane (OV-1 701). Enantioselectivity obtained with TBDE-beta-CD was compared with that of tyldimethylsilyl-2,3-di-O-methyl-beta-cyclodextrin (TBDM-beta- CD). Better enantioselectivity was obtained with TBDE-beta-CD than wit h TBDM-beta-CD for the test chiral compounds studied, This is probably due to greater effect of the increased hydrophobicity of TBDE-beta-CD which favors inclusion of the analytes than the effect of increased s teric hindrance, With TBDP-beta-CD the less polar lactones are well se parated due most likely to increased hydrophobicity of the propyl grou ps while the more polar are not well resolved. For TBDP-beta-CD it is likely that the unfavorable steric hindrance is predominant over the f avorable hydrophobicity of the propyl groups, thus hindering the forma tion of inclusion complexes of the alcohols with TBDP-beta-CD, TBDE-al pha-CD was also a valuable chiral selector for the separation of small chiral molecules such as simple secondary alcohols and nitro-substitu ted alcohols.