Structure elucidation of the adducts formed by fjord region dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxides with deoxyguanosine

(±)-anti-Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(±)- anti-DB[a,l]PDE} was reacted with deoxyguanosine (dG) in dimethylformamide at 100 °C for 30 min, and two sets of adducts were isolated: a mixture of (±)-anti-cis- and -trans-N²dG (43%) and a mixture of (±)anti-cis- and - trans-N7Gua (45%). Both are mixtures of four stereoisomers that cannot be separated by HPLC. Similarly, (±)-syn-DB[a,l]PDE was reacted with dG under the same conditions, and (±)-syn-cis- and -trans-N²dG (38%) and (±)-syn- cis- and -trans-N7Gua (59%) were obtained. The structures of the adducts were determined by a combination of NMR and fast atom bombardment mass spectrometry. By reacting (-)-anti-DB[a,l]PDE or (+)-syn-DB[a,l]PDE with dG under the same conditions, however, optically pure N²dG and N7Gua isomers were obtained: (-)-anti-cis-N²dG (12%), (-)-anti-trans-N²dG (17%), (-)- anti-trans-N7Gua (43%), (+)-syn-cis-N²dG (7%), (+)-syn-trans-N²dG (3%), (+)-syn-cis-N7Gua (36%), and (+)-syntrans-N7Gua (22%). The structures of the optically pure adducts were assigned by NMR. syn-and anti-DB[a,l]PDE-N²dG adducts can be distinguished by fluorescence line-narrowing spectroscopy (FLNS). Moreover, distinction between cis- and trans-stereochemistry of the adducts is also straightforward by FLNS, because the FLN spectra for the four DB[a,l]PDEN²dG adducts, anti-cis, anti-trans, syn-cis, and syn-trans, are spectroscopically unique.