Novel cinchona alkaloid carbamate C-9-dimers as chiral anion-exchange typeselectors for high-performance liquid chromatography

Nine new quinine (QN) carbamate C-9-dimers (QN-X-QN), with different alipha tic and cyclic spacers (X), have been synthesized and immobilized onto poro us silica gel for HPLC. The chiral discriminating behavior of these "dimeri c" anion-exchange type chiral stationary phases (CSPs) has been investigate d in detail, to elucidate the role of the presence of a second QN subunit o n the chiral selector (SO), as well as the influence of the structure and l ength of the spacer, on the overall chiral recognition of a set of N-deriva tized amino acids and other acidic drugs. The bulkiness of the intermediate spacer tuned the chiral recognition abilities of these SOs, with the 1,3-a damantylen-derived CSP being the one that led to the best separations. Shor ter spacers reduced the chiral discrimination abilities of the "dimeric" se lectors, with the n-hexylen bridge being the most favorable distance to all ow a nearly independent interaction of the two QN subunits with the racemic analytes. The comparison to five "monomeric" CSPs showed that the "dimeric " ones usually retain the chiral analytes more strongly, though the enantio separation is not improved. Nevertheless, the exceptional resolution abilit ies of dimeric SOs with a trans-1,2-diaminocyclohexylen-bridge for the sepa ration of DNP-derivatives of amino acids and certain acidic drugs of therap eutical interest (e.g., profens) seemed to be superior to most of the other CSPs. (C) 2000 Elsevier Science B.V. All rights reserved.