COMPARISON OF CHIRAL RECOGNITION CAPABILITIES OF CYCLODEXTRINS FOR THE SEPARATION OF BASIC DRUGS IN CAPILLARY-ZONE-ELECTROPHORESIS

The enantiomeric separation of some racemic anti-histamines and anti-m alarials, namely (+/-)-pheniramine, (+/-)-brompheniramine, (+/-)-chlor pheniramine, (+/-)-doxylamine, and (+/-)-chloroquine, was investigated by capillary zone electrophoresis. The enantiomeric separation of fiv e compounds was obtained by addition of similar to 7 mM (1%, w/v) sulf ated-beta-cyclodextrin into the buffer as a chiral selector. The effec ts of sulfated-beta-cyclodextrin concentration and buffer pH on migrat ion and resolution are discussed, Two other cyclodextrins, carboxyethy lated-beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin were also investigated. Four of the racemic compounds were resolved using 14 mM (2%, w/v) carboxyethylated-beta-cyclodextrin while 28 mM (4% w/v) hydr oxypropyl-beta-cyclodextrin resolved only two of them. It was found th at the type of substituent and the degree of substitution on the rim o f the CD structure played an important role in enhancing the chiral re cognition. Cyclodextrins with negatively charged substituents and high er degree of substitution on the rim of the structure proved to give b etter resolution to the cationic racemic compounds compared with cyclo dextrin with neutral substituents. This is due to the countercurrent m obility of the negatively charged cyclodextrin relative to the cationi c analytes thus allowing for a smaller difference in interaction const ants to achieve a successful resolution of enantiomers. Furthermore, l ower concentrations of negatively charged cyclodextrins were necessary to achieve the equivalent resolutions as compared with the neutral on es. (C) 1998 Elsevier Science B.V.