Use of a zwitterionic cyclodextrin as a chiral agent for the separation of enantiomers by capillary electrophoresis

The purity and enantioselectivity of a novel chiral agent, the zwitterionic mono-(6-delta-glutamylamino-6-deoxy)-delta-cyclodextrin (beta-CD-Glu), were studied by capillary electrophoresis. Chiral separation of the enantiomers of chlorthalidone was obtained at pH 2.3, a pH at which beta-CD-Glu is partially protonated. Comparison with the cationic mono-(6-amino-6-deoxy)-beta-cyclodextrin (beta-CD-NH2) enantioselectivity clearly shows that the greater the difference in mobility between the free analyte and the analyte-cyclodextrin complex, the better the resolution. Hydrobenzoin enantiomers were separated at pH 11.2, a pH at which beta-CD-Glu is anionic. Under these conditions, the migration order was opposite to that observed in the presence of beta-CD-NH2 at pH 2.3. When no separation was obtained directly with beta-CD-Glu, a dual cyclodextrin system was developed. Carprofen enantiomers were resolved at pH 2.3 in the presence of a beta-CD-Glu/trimethyl-beta-cyclodextrin (TM-beta-CD) system in which the charged CD confers a non-zero mobility to the analyte, while the neutral CD allows chiral recognition.