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-ll,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- & -trans-N2dG (43%) and a mixture of (_+-)anti-cis- & -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- & -trans-N2dG (38%) and (±)-syn-cis- & -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 (+)M-syntrans-N7Gua (22%). The structures of the optically pure adducts were assigned by NMR. synand anti-DB[a,l]PDE-NMG 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.