Synthesis and Structure Determination of the Adducts Formed by Electrochemical Oxidation of the Potent Carcinogen Dibenzo[a,I]pyrene in the Presence of Nucleosides

Because dibenzo[a,l]pyrene (DBP) is the most potent known carcinogenic aromatic hydrocarbon, reference adducts formed by reaction of deoxyribonucleosides with electrophilic intermediates of DBP are essential for identifying the structures of adducts formed in biological systems. Electrochemical oxidation of DBP in the presence of nucleosides leads to adducts from DBP^•+. When 6.8 equiv of charge are consumed, three adducts are formed with dG: 7-(DBP-10-yl)Gua (89%), 8-(DBP-10-yl)dG (2%), and 8-(DBP-10-yl)Gua (2%). With 10 equiv of charge, however, only two adducts are formed: 7-(DBP-10-yl)Gua (89%) and 8-(DBP-10-yl)Gua (4%). Anodic oxidation of 8-(DBP-10-yl)dG yields 8-(DBP-10-yl)Gua. Anodic oxidation of DBP in the presence of G produces 7-(DBP-10-yl)Gua (27%) and 8-(DBP-10-yl)G (9%). Anodic oxidation of DBP in the presence of dA affords two adducts, N⁶-(DBP-10-yl)dA (28%) and 7-(DBP-10-yl)Ade (12%), whereas anodic oxidation in the presence of A produces only N⁶-(DBP-10-yl)A (24%). The structures of the adducts were elucidated by using UV, NMR, and MS. Formation of these adducts demonstrates that DBP^•+ reacts at C-10 with nucleophiles. The most reactive nucleophilic groups for the Gua moiety are the N-7 and C-8, whereas for the Ade moiety they are N-7 and the 6-amino group.