EFFECT OF THE CONFIGURATION OF THE SUBSTITUENTS OF DERIVATIZED BETA-CYCLODEXTRIN BONDED PHASES ON ENANTIOSELECTIVITY IN NORMAL-PHASE LIQUID-CHROMATOGRAPHY

(R)-(-)-, (S)-(+)- and racemic 1-(1-naphthyl)ethylcarbamate derivatives of beta-cyclodextrin (beta-CD) bonded phase were used to successfully resolve a large variety of enantiomers in the normal-phase mode. The selectivity (alpha) and retention (k') of these new chiral packings in the normal-phase mode are somewhat analogous to a reciprocal Pirkle-type phase. Also, many of the enantiomers resolved on these new phases were not resolvable on the native beta-CD phase in the reversed-phase mode or on the naphthylvaline type pi-complex, hydrogen bonding phases. Comparison of the selectivity and retention of the (R)-, (S)- and racemic carbamate phases revealed that both the carbamate substituent and the cyclodextrin moieties contribute to chiral recognition. The selectivity of these phases was found to be a function not only of the configuration of the substituent on the CD but also was dependent on the number of substituents (degree of substitution). More importantly, the results indicate that enantioselectivity on these phases arises from two modes of chiral recognition. In some cases, the chiral selectivity of the one configuration of the substituent and the CD combine synergistically while the chiral selectivity of the opposite configuration of the substituent and the CD combine antagonistically. For some compounds, changing the carbamate substituent configuration resulted in a reversal of the elution order.