Assignment of Absolute Configuration to Metabolically Formedtrans-Dihydrodiols of Dibenzo[a,l]pyrene by the Exciton Chirality Method Using a New Red-Shifted Chromophore

Absolute configuration was assigned to the enantiomers of the metabolically formed trans-11,12-dihydrodiol of dibenzo[a,l]pyrene by application of a CD spectroscopic method. For this purpose (±)-trans-11,12-dihydrodiol was converted to its diastereomeric bis(menthoxyacetates) followed by preparative separation of the diastereomers on silica gel. Hydrolysis of the two diastereomers gave the (+)- and (−)-11,12-dihydrodiols. To achieve assignment of the absolute configuration by the nonempirical exciton chirality method both the (+)- and (−)-dihydrodiol were transformed to their bis-4[4′-(dimethylamino)phenylazo]benzoates. The CD spectra of the bis-4[4′-(dimethylamino)phenylazo]benzoates revealed that (R,R)-configuration is associated with the (−)-11,12-dihydrodiol, whereas the (+)-11,12-dihydrodiol possesses (S,S)-configuration. Based on this assignment the absolute structures of the stereoselectively synthesized enantiomeric fjord-region 11,12-dihydrodiol 13,14-epoxides being potential ultimate carcinogenic metabolites of DB[a,l]P have also been unequivocally determined.