Enantioselective anion exchangers based on cinchona alkaloid-derived carbamates: Influence of C-8/C-9 stereochemistry on chiral recognition

Four diastereomeric chiral stationary phases (CSPs) based on quinine, quini dine, epiquinine, and epiquinidine tert-butyl carbamate selectors were synt hesized and evaluated under ion exchange HPLC conditions with a set of race mic N-acylated and N-oxycarbonylated alpha-amino acids as selectands. The e nantioseparation potential of quinine- and quinidine-derived CSPs proved to be far superior to that of their C-9-epimeric congeners. The absolute conf iguration of C-9 stereogenic center of the cinchonan backbone of these sele ctors was identified as the structural feature controlling the elution orde r. Guided by an X-ray structure of a most favorable selector-selectand comp lex and the observed chromatographic enantioseparation data, a chiral recog nition model was advanced. The contributions of ion-pairing, pi-pi donor-ac ceptor, hydrogen bonding and steric interactions were established as crucia l factors. (C) 1999 Wiley-Liss, Inc.