Absolute configuration ofcis-5,6-dihydrodiol enantiomers derived from helical conformers of 1,12-dimethylbenz[a]anthracene

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Abstract
1,12‐Dimethylbenz[α]anthracene (1,12‐DMBA) cis‐5,6‐dihydrodiol was synthesized by oxidation of 1,12‐DMBA with osmium tetroxide in pyridine in low yield (⩽3%) and was purified by sequential use of reversed‐phase and normal‐phase HPLC. Two pairs of 1,12‐DMBA cis‐5,6‐dihydrodiol enantiomers, derived from P (right‐handed helix) and M (left‐handed helix) conformers, were eluted as a single chromatographic peak on both reversed‐phase and normal‐phase HPLC. However, these four enantiomers were resolved by sequential use of two chiral stationary phase (CSP) HPLC columns. CSP (Pirkle type I) columns were packed with either (R)‐N‐(3,5‐dinitrobenzoyl)phenylglycine or (S)‐N‐(3,5‐dinitrobenzoyl)leucine, which is ionically bonded to γ‐aminopropylsilanized silica. Absolute configurations of enantiomers were determined by comparing their circular dichroism spectra with those of conformationally similar cis‐5,6‐dihydrodiol enantiomers of 4‐methylbenz[α]anthracene and 7,12‐dimethylbenz[α]‐anthracene with known absolute stereochemistry.