Abstract (eng)
Liquid chromatography (LC) by means of chiral stationary phases (CSPs) is of central importance both as an analytical tool for the separation of enantiomers and also on a preparative scale to give access to bulk quantities of highly enantiopure chiral compounds.
In this work the development of several novel ion exchanger type CSPs based on synthetic low molecular mass chiral selectors (SOs) as the enantioselective functional entities, and their evaluation for enantiomer separations in HPLC are presented.
At first, strong cation exchanger (SCX) type SOs were prepared that contained a beta-amidocyclohexanesulfonic acid as chiral moiety. The corresponding CSPs allowed the baseline enantioseparation of a series of chiral basic drugs. In a separate study on the SCX-type SOs, and in combination with a quinidine-based, oppositely charged anion-exchanger (AX) type SO using HPLC and X-ray diffraction, the molecular recognition mechanism of these AX- and CX-type SOs could be depicted. Furthermore, the SCX-type CSP was evaluated for the nonenantioselective analysis of a series of basic Cinchona alkaloids where it turned out to be an alternative, complementary stationary phase to the reversed-phase packing materials commonly used in this context. The described SCX-SO was also applied in a comparison of capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) for enantioseparations as well as in a study that deconvoluted the electrokinetic and chromatographic contributions to analyte migration in enantioselective ion-exchange CEC. Finally, a novel type of ion-exchanger CSP was developed by combining key motifs of both anion- and cation-exchanger type CSPs into one, now zwitterionic SO molecule. The resulting zwitterionic (ZWIX) CSPs not only essentially combined the enantioselective properties of the parent AX- and CX-type CSPs, but in addition also showed excellent enantioselectivities for zwitterionic amino acids and peptides. Mechanistically the zwitterion exchange could be described by a simultaneous double ion pairing event. Due to the overlaid equilibra particular effects on retention and resolution could be observed in the course of mobile phase optimization.