High-performance liquid chromatographic enantioseparation of cationic 1,2,3,4-tetrahydroisoquinoline analogs on Cinchona alkaloid-based zwitterionic chiral stationary phases.

The stereoisomers of 1,2,3,4-tetrahydroisoquinoline analogs were resolved for the first time by applying a polar ionic mobile phase on a quinine or a quinidine moiety fused with a chiral sulfonic acid-type chiral selector immobilized on silica [Chiralpak ZWIX(+)™ and Chiralpak ZWIX(-)™]. The effects of the nature and concentrations of the mobile phase components and additives and temperature on the retention and enantioseparation on the investigated chiral columns were studied. Experiments were performed in the temperature range 10-50 °C. Thermodynamic parameters were calculated from plots of ln α versus 1/T. The separations were generally enthalpy-controlled, but entropy-controlled separation was also observed below 30 °C. The enantiomer elution order was determined in some cases and was observed to be opposite on the ZWIX(+)™ and ZWIX(-)™ columns. Our results contribute to a better understanding of the enantiorecognition mechanism of chiral bases with chiral zwitterionic selectors.