TEMPERATURE-DEPENDENCE OF CHIRAL DISCRIMINATION IN SUPERCRITICAL-FLUID CHROMATOGRAPHY AND HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Chiral separations of related compounds within a series of potassium channel activator (KCA) analogues were compared by supercritical fluid chromatography (SFC) and high-performance liquid chromatography (HPLC) at several temperatures between 0 degrees and 52 degrees C. Mobile phases as close as possible in performance were selected for the two modes of analysis, and the same chiral stationary phase (CSP) was used, namely, cellulose tris(3,5-dimethylphenyl-carbamate) (Chiralcel-OD). Two of the compounds, which differed only by replacement of a benzoyl group by a n-pentanoyl group, showed quite strikingly different temperature dependencies. These indicate, that one compound is above, and the other below, its isoenantioselective temperature (T-150), at which separation of enantiomers is not possible. The thermodynamic parameters for these chiral discriminations support the conclusion that, in spite of their very similar structures, quite different chiral recognition factors operate for these two racemic mixtures.