Facile synthesis of positively charged monosubstituted α- and γ-cyclodextrins for chiral resolution of anionic racemates

New positively charged monosubstituted alpha- and gamma-cyclodextrins at the primary face were synthesized in good yields by displacement of the monotosylates of alpha- and gamma-cyclodextrin with amine, alkylamines or alkylimidazoles. The influence of CD's cavity size on the resolution abilities of CD derivatives towards model analytes, that is, dansyl amino and carboxylic acids, were investigated. Results show that the formation of the inclusion complex might play an important role in chiral recognition, in that cationic gamma-CD derivatives gave better resolution abilities than their alpha- and gamma-CD analogues, presumably due to tight fit between CD hosts and the anionic guest racemates. (C) 2007 Elsevier Ltd. All rights reserved.