Single Isomer -Heterocyclic Cyclodextrin Derivatives as Chiral Selectors in Capillary Electrophoresis.

In order to better understand the chiral recognition mechanisms of positively charged cyclodextrin (CD) derivatives, the synthesis, the p determination by H nuclear magnetic resonance (NMR)-pH titration and a comparative chiral capillary electrophoretic (CE) study were performed with two series of mono-substituted cationic single isomer CDs. The first series of selectors were mono-(6--pyrrolidine-6-deoxy)-β-CD (PYR-β-CD), mono-(6--piperidine-6-deoxy)-β-CD (PIP-β-CD), mono-(6--morpholine-6-deoxy)-β-CD (MO-β-CD) and mono-(6--piperazine-6-deoxy)-β-CD (PIPA-β-CD), carrying a pH-adjustable moiety at the narrower rim of the cavity, while the second set represented by their quaternarized, permanently cationic counterparts: mono-(6--(-methyl-pyrrolidine)-6-deoxy)-β-CD (MePYR-β-CD), mono-(6--(-methyl-piperidine)-6-deoxy)-β-CD (MePIP-β-CD), mono-(6--(-methyl-morpholine)-6-deoxy)-β-CD (MeMO-β-CD) and mono-(6--(4,4--dimethyl-piperazine)-β-CD (diMePIPA-β-CD). Based on pH-dependent and selector concentration-dependent comparative studies of these single isomer -heterocyclic CDs presented herein, it can be concluded that all CDs could successfully be applied as chiral selectors for the enantiodiscrimination of several negatively charged and zwitterionic model racemates.