Evaluation of the contribution to enantioselectivity of quinine and quinidine scaffolds in chemically and physically mixed chiral selectors

Three "dimeric" C(9)-carbamates of quinine (QN) and quinidine (QD), that is, QN-QN, QD-QD, and QN-QD (chemically prepared mixture of the two cinchona-derived subunits), separated by an ethylene spacer were synthesized and used as chiral selectors for HPLC and capillary electrophoresis (CE) for the resolution of chiral acids. The chiral recognition abilities of these dimers and of several physically prepared mixtures thereof were compared in order to estimate the contribution of every cinchona scaffold to the overall enantioselectivity. The diverse phenomena observed in nonaqueous capillary electrophoresis (NACE), either using the selector added to the background electrolyte (BGE) in the total filling or partial filling mode, led us to rationalize, taking into account the relative mobilities of the chiral selectors in the capillary. The chromatographic and electrophoretic properties were compared with those of the corresponding "monomeric" QN and QD carbamates.