Abstract
Three new β‐cyclodextrin derivatives, heptakis(6‐O‐isopropyldi‐methylsilyl‐2,3‐di‐O‐ethyl)‐β‐cyclodextrin, heptakis(6‐O‐thexyldi‐methylsilyl‐2,3‐di‐O‐ethyl)‐β‐cyclodextrin, and heptakis(6‐O‐cy‐clohexyldimethyl‐2,3‐di‐O‐ethyl)‐β‐cyclodextrin (IPDE‐β‐CD, TXDE‐β‐CD, and CHDE‐β‐CD), were synthesized and the enan‐tioselectivities of these three CD derivatives and heptakis(6‐O‐tert‐butyldimethylsilyl‐2,3‐di‐O‐ethyl)‐β‐cyclodextrin (TBDE‐β‐CD) were compared for GC separation of a range of chiral test com‐pounds. In particular TXDE‐β‐CD showed much higher enentio‐selectivity than TBDE‐β‐CD. Enentioselectivities of IPDE‐β‐CD and CHDE‐β‐CD are somewhat lower than that of TXDE‐β‐CD and CHDE‐β‐Cd are somewhat lower than that of TXDE‐β‐CD. These observations are indicative of significant effects of subtle changes in the structure of the 6‐O‐substituent on the enantioselec‐tivity of the β‐CD derivatives. The difference in enantioselectivities of the 6‐O‐substituted CD derivatives were explained in terms of relative contributions of the effects of hydrophobicity and steric hindrance of the substituent to the inclusion process. CHDE‐β‐CD showed the lowest enantioselectivity among the threederivatives. It is likely that the unfavorable steric hindrance of the bulky cyclo‐hexyl group plays a greater role than the favorable hydrophobicity effect of the cyclohexyl group in the inclusion process in CHDE‐β‐CD. IPDE‐β‐CD showed lower selectivity than TXDE‐β‐CD and TBDE‐β‐CD. In the case of these CD derivatives having acyclic substituents the relative hydrophobicity of the substituent seems to be a dominant factor affecting the inclusion process. Isopropyl groups factor affecting the inclusion process. Isopropyl groups are less hydrophobic than thexyl and tert‐butyl groups.