Synthesis and Characterization of Adducts Formed in the Reactions of Safrole 2',3'-Oxide with 2'-Deoxyadenosine, Adenine, and Calf Thymus DNA

Safrole (1) is a natural product found in herbs and spices. Upon uptake, it can be metabolized to safrole 2',3'-oxide [(+/-)-SFO, 2], which can react with DNA bases to form DNA adducts. The reactions of 2 with 2'-deoxyadenosine (3) and adenine (8) under physiological conditions (pH 7.4, 37 degrees C) were carried out to characterize its possible adducts with adenine. Four adducts were isolated by reverse-phase liquid chromatography and their structures were characterized by UV/Vis, 1H and 13C NMR spectroscopy and MS. The reaction of 2 with 3 produced two regioisomers, N1?-SFO-dAdo (4) and N6?-SFO-dAdo (5), in 4.24.5?% yield, and the reaction of 2 with 8 generated N3?-SFO-Ade (9) and N9?-SFO-Ade (10) in 1.02.4?% yield. Using HPLCESI-MS/MS, we traced the amounts of the four adducts formed when calf thymus DNA (10 mg) was treated with 2 (60 mu mol) and the levels of 4, 5, and 9 were determined to be 2000, 170, and 660 adducts per 106 nucleotides, respectively. Adduct 10 was not detected under these conditions. These results suggested that stable DNA adducts of 2 were formed in vitro, and further studies on the formation of these DNA adducts in vivo may help to elucidate their role in safrole carcinogenicity.