Synthesis and characterization of polycyclic aromatic hydrocarbon o-quinone depurinating N7-guanine adducts

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants which may cause cancer and require metabolic activation to exert their carcinogen ic effects. One pathway of activation involves the dihydrodiol dehydrogenas e-catalyzed oxidation of non-K region trans-dihydrodiols to yield catechols , which autoxidize to form reactive o-quinones. As a step toward identifyin g the spectrum of PAH o-quinone-DNA adducts that may form in biological sys tems, depurinating PAH o-quinone-guanine adducts were synthesized. Naphthal ene-1,2-dione, phenanthrene-l, 2-dione, and benzo[alpha]pyrene-7,8-dione we re reacted with 5 equiv of 2'-deoxyguanosine (dGuo) under acidic conditions (1:1 acetic acid/water). The products were purified by reversed-phase HPLC , characterized by a combination of UV spectroscopy, electrospray ionizatio n/tandem mass spectrometry, and high-field proton nuclear magnetic resonanc e spectroscopy, and identified as 7-(naphthalene-1,2-dion-4-yl)guanine (MH, mit 308), 7-(phenanthrene-1,2-dion-4-yl)guanine (MH+, mit 358) and 7-(ben zo[a]pyrene-7,8-dion-10-yl)guanine (MH+, mit 432), respectively. Reaction a t N7 of dGuo leads to cleavage of the glycosidic bond, producing depurinati ng adducts. Reaction of phenanthrene-1,2-dione with calf thymus DNA led to the formation of the corresponding depurinating adduct. The loss of modifie d bases in DNA generates apurinic sites which, if unrepaired, can lead to m utations and thus cellular transformation. These synthesized PAH o-quinone- N7-guanine adducts can be used as standards to identify such adducts in vit ro and in vivo.