Synthesis and structure determination of the adducts of the potent carcinogen 7,12-dimethylbenz[a]anthracene and deoxyribonucleosides formed by electrochemical oxidation: Models for metabolic activation by one-electron oxidation

Article abstract of DOI:10.1021/ja00031a047

Anodic oxidation of 7,12-dimethylbenz[a]anthracene (7,12-DMBA) in the presence of dG yields four adducts and one oxygenated derivative of 7,12-DMBA: 7-methylbenz[a]anthracene (MBA)-12-CH₂-C8dG (13%), 7-MBA-12-CH₂-N7Gua (55%), 12-MBA-7-CH₂-N7Gua (12%), 7-MBA-12-CH₂-C8Gua (10%), and 7,12-(CH₂OH)₂-BA (10%). The first three are primary products of the electrochemical reaction, whereas the last two are secondary products. Binding occurs predominantly at the 12-CH₃ group of 7,12-DMBA and specifically to the N-7 and C-8 of Gua. On the other hand, anodic oxidation of 7,12-DMBA in the presence of dA gives only two detectable adducts: 7-MBA-12-CH₂-N7Ade (45%) and 12-MBA-7-CH₂-N3Ade (55%). Binding at the 12-CH₃ group is specific for the N-7 of Ade, whereas the 7-CH₃ group of 7,12-DMBA is specific for the N-3 of Ade. Structures of the adducts were elucidated by NMR and fast atom bombardment tandem mass spectrometry (FAB MS/MS). The adducts were also investigated by fluorescence line narrowing spectroscopy (FLNS). Both the FAB MS/MS and FLNS techniques can be used to distinguish between the adducts formed at the 7-CH₃ and 12-CH₃ groups of 7,12-DMBA (i.e., between 7-MBA-12-CH₂-N7Gua and 12-MBA-7-CH₂-N7Gua and between 7-MBA-12-CH₂-N7Gua and 7-MBA-12-CH₂-C8Gua). FLNS can distinguish 12-MBA-7-CH₂-N3Ade from 7-MBA-12-CH₂-N7Ade. On the other hand, the distinction between 7-MBA-12-CH₂-C8Gua and 7-MBA-12-CH₂-C8dG is straightforward by FAB MS but very difficult by FLNS. The electrochemical synthesis not only provides a demonstration of the specific reactivity of nucleosides and 7,12-DMBA under oxidizing conditions but is also a source of the necessary reference materials for studying the 7,12-DMBA-DNA adducts formed in biological systems. Furthermore, the analytical methodology is now appropriate for supporting in vivo studies of 7,12-DMBA-DNA adducts. A mechanism is proposed, although there are not sufficient data to prove it.