Quinine and quinidine derivatives as chiral selectors I. Brush type chiral stationary phases for high-performance liquid chromatography based on cinchonan carbamates and their application as chiral anion exchangers

Abstract

Quinine and quinidine carbamates, respectively, have been immobilized onto porous silica utilizing two different types of spacer and/or grafting modes, obtaining four brush type chiral stationary phases (CSPs). These CSPs have preferentially been operated with buffered aqueous mobile phases to resolve the enantiomers of acidic analytes involving ion pair mechanisms as the dominating binding and/or retention principle beside additional adsorption towards the modified silica surface. The spectrum of successfully resolved racemates contains chiral aryl-, aryloxy- and arylthiocarboxylic acids, as well as N-derivatized amino acids (DNB-, B-, Ac-, F-, DNP-, DBD-, Fmoc-, Boc-, Z-, DNS-amino acids, etc.) and many other chiral acids including also sulfonic, phosphonic and phosphoric acids. The influence of mobile phase parameters, as well as of structure variations of analytes on retention and enantioselectivity was evaluated. Thus, a chromatographically derived tentative chiral recognition model is proposed for DNB-amino acids which are resolved into enantiomers with exceptionally high α-values (e.g., DNB-Leu with an α-value of about 7).