Structural features affecting chiral resolution of cannabimimetic enantiomers by amylose 3,5‐dimethylphenylcarbamate chiral stationary phase

Abstract

AbstractThe effect of structural features of six pairs of enantiomers of cannabimimetic compounds on their chromatographic resolution on an amylose tris(3,5‐dimethylphenylcarbamate) chiral stationary phase was studied using various compositions of n‐hexane with 2‐propanol and ethanol. Structural analysis by molecular mechanics was also performed to verify that the 3D conformation within this family of compounds was preserved with substitution. The homologous enantiomeric pairs showed better resolution when there was an additional OH group near the chiral centers (position 7 on the cannabinoid structure). Better resolution was observed also for the enantiomeric pair that had the smaller alkyl side chain. These differences indicated that the additional OH group contributed to a better discrimination of the enantiomers by the chiral sites of the stationary phase and that the bulkier alkyl side chain reduced it. The chromatographic resolution of two enantiomeric pairs of nonclassical cannabinoids HU‐249 and HU‐250, HU‐255 and HU‐256, was compared both in ethanol and 2‐propanol. Both enantiomeric pairs showed relatively high resolution and selectivity, but the rigid benzofuran analogs (HU‐249 and HU‐250) exhibited better resolution using 2‐propanol, in spite of the flexibility of the open chain analog (HU‐255 and HU‐256) and its additional OH group. The elution order of all the cannabinoids was (+)/(−) using both solvents. Unusual solvent effects were displayed by one enantiomeric pair, Δ6‐THC, which was resolved easily using 2‐propanol, but whose elution order reversed with 1% ethanol in the mobile phase. Partial separation was obtained at 5% ethanol [elution order (+)/(−)] and full separation was obtained at 0.5% ethanol [elution order (−)/(+)]. © 1995 Wiley‐Liss, Inc.