Elution order—absolute configuration relationship of k-region dinhydrodiol enantiomers of benz[ a]anthracene derivatives in chiral stationary phase high-performance liquid chromatography

Abstract

The direct resolution of K-region cis and trans-hydrodiol enantiomers of 14 unsubstituted and methyl- and bromo-substituted benz[ a]anthracene (BA) derivatives was investigated by high-performance liquid chromatography with commercially available columns, packed with γ-aminopropylsilanized silica to which eitehr ( R)-N-(3,5-dinitrobenzoyl)phenylglycine ( R-DNBPG) or ( S)-N-(3-5-dinitrobenzoyl)leucine ( S-DNBL) is either ionically or covalently bonded. BA derivatives used in this study include: BA, 1-methyl-BA, 4-methyl-BA, 7-methyl-Ba, 8-methyl-Ba, 10-methyl-BA, 11-methyl-BA, 12-methyl-Ba, 7,12-methyl-BA, 7-bromo-Ba, 7-bromo-1-methyl-Ba, 7-bromo-11-methyl-BA, 7-bromo-12-methyl-BA, and 3-methylcholanthrene. The enantiomers of BA trans-5,6-dihydrodiol were the only compounds not resolved by any of the four chirals stationary phases (CSPs) tested. The results indicate that conformational preference of the hydroxyl group is one of the most important factor in determining the elutionorder of dihyrodiol enantiomers. The presence and the location of a substituent and the molecular size and shape of the dihydrodiols can significantly affect the efficiency of enantiomeric resolution. In general, the ionically bonded R-DNBPG provides the best resolution of enantiomeric quasidiequatorial trans-dihydrodiols and the R,R enantiomers ar consistently more strongly retained. In contranst, the enantiomeric pairs of quasidiaxial trans-dihydrodiols are generaly better resolved by the covalently bonded R-DNBPG, and the S,S enantiomers are more strongly retained. The enantiomers of cis-dihydrodiols having hydroxyl groups that adopt quasiequatorial-quasiaxial and/or quasiaxial-quasiequatorial conformations are more consistently resolved by the ionically bonded S-DNBL and in all cases the S,R enantiomers are more strongly retained. Thus, it is possible to choose a CSP which resolves the K-region dihydrodiol enantiomers with a predictable elution order.