Enantioselective high-performance liquid chromatographic separation of fluorinated ß- phenylalanine derivatives utilizing Cinchona alkaloid-based ion-exchanger chiral stationary phases: Enantioselective separation of fluorinated ß-phenylalanine derivatives

The enantioselective separation of newly synthesized fluorine-substituted β-phenylalanines has been performed utilizing Cinchona alkaloid-based ion-exchanger chiral stationary phases. Experiments were designed to study the effect of eluent composition, counterion content, and temperature on the chromatographic properties in a systematic manner. Mobile phase systems containing methanol or mixtures of methanol and acetonitrile together with acid and base additives ensured highly efficient enantioseparations. Zwitterionic phases [Chiralpak ZWIX (+) and ZWIX(-)] were found to provide superior performance compared to that by the anion-exchangers (Chiralpak QN-AX and QD-AX). A detailed thermodynamic characterization was also performed by employing van't Hoff analysis. Using typical liquid chromatographic experimental conditions, no marked effect of the flow rate could be observed on the calculated thermodynamic parameters. In contrast, a clear tendency has been revealed about the effect of the eluent composition on the thermodynamics for the zwitterionic phases.