Synthesis of adducts formed by iodine oxidation of aromatic hydrocarbons in the presence of deoxyribonucleosides and nucleobases

Abstract

Polycyclic aromatic hydrocarbons (PAH) undergo two main pathways of metabolic activation related to the initiation of tumors: one-electron oxidation to give radical cations and monooxygenation to yield bay-region diol epoxides. Synthesis of standard adducts is essential for identifying biologically formed adducts. Until recently, radical cation adducts were synthesized by oxidation of the PAH in an electrochemical apparatus, not readily available in many organic chemistry laboratories. We have developed a convenient and efficient method for synthesizing PAH-nucleoside adducts by using I2 as the oxidant. Adducts of benzo[a]pyrene (BP), dibenzo[a, l]pyrene (DB[a,l]P), and 7,12-dimethylbenz[a]anthracene were synthesized with deoxyguanosine (dG), deoxyadenosine, guanine (Gua), or adenine in either Me2SO or dimethylformamide (DMF) with or without AgClO4. When, for example, the potent carcinogen BP was dissolved in DMF in the presence of 3 equiv of I2, 5 equiv of dG, and 1 equiv of AgClO4, 45% of the BP was converted to BP-6-N7Gua. When BP was placed under the same reaction conditions in the absence of AgClO4, the extent of formation of BP-6-N7Gua decreased to 30%. When the potent carcinogen DB[a,l]P was dissolved in DMF in the presence of 3 equiv of I2, 5 equiv of dG, and 1 equiv of AgClO4, 43% of the DB[a,l]P was converted to DB[a,l]P-10-N7Gua. In the more polar solvent Me2SO under the same reaction conditions, however, the yield of DB[a,l]P-10-N7Gua was only 20%. Synthesis of adducts with the oxidant I2 is more convenient and, in some cases, more efficient than synthesis by electrochemical oxidation. This method simplifies the synthesis of PAH-nucleoside and nucleobase adducts that are essential for studying biologically formed PAH-DNA adducts.