Synthesis and characterization of deoxyguanosine–benzoquinone adducts

Abstract

Benzene expresses its carcinogenic potential in humans largely in the form of acute leukemia. Because an understanding of the formation of DNA adducts by benzene metabolites may help to explain the etiological role they play in benzene-induced bone marrow disease, we have synthesized, isolated and characterized adducts formed by the reaction of deoxyguanosine with hydroquinone and p-benzoquinone, two toxic metabolites of benzene. [3H]Deoxyguanosine and [14C]hydroquinone reacted in neutral aqueous buffer containing iron to form two dual-labeled products, which were separated using HPLC. When p-benzoquinone was substituted for hydroquinone, the same adducts were formed in the absence of added iron. The ultraviolet and fluorescence spectra of the less polar adduct, called Adduct 2, were distinctly different from the spectra of the starting materials. NMR and mass spectrometry suggested a compound with a mass of 357 with the p-benzoquinone moiety bound to the N-1 and N2 positions of deoxyguanosine. Based on these data it is proposed that Adduct 2 is (3'OH)benzetheno(1,N2)deoxyguanosine. The more polar product, Adduct 1, was found to have a unique ultraviolet spectrum but did not appear to be fluorescent. Both adducts were observed after calf thymus DNA was incubated with hydroquinone and digested to its constituent nucleosides.

An Overview of Benzene Metabolism

“…To chemically characterize the DNA adducts formed, adducts were prepared in vitro by reacting deoxynucleosides or deoxynucleoside monophosphates with either p-benzoquinone or hydroquinone in the presence of an oxidizing agent. The combination of UV, fluorescence, mass, and nuclear magnetic resonance spectrometry was first used by Jowa et al (29) to identify 3'-OH-1,N2-benzetheno-2'-deoxyguanosine as a major deoxyguanosine adduct ( Figure 5). …”

Phenylguanine Found in Urine after Benzene Exposure

“…Identification of (3'OH)benzetheno-(N1,N2)-deoxyguanosine as a DNA adduct by Jowa et al (3,14) was confirmed by Snyder et al (4) and Kaur et al. (5).…”

Synthesis of the Fully Protected Phosphoramidite of the Benzene-DNA Adduct,N2-(4-Hydroxyphenyl)-2′-Deoxyguanosine and Incorporation of the Later into DNA Oligomers

“…[10][11][12] Both metabolites form exocyclic benzetheno adducts with dG, dA and dC. [13][14][15][16][17] Although they were not detected 4 in tissues such as the bone marrow by 32 P-postlabeling, [18,19] their in vivo formation by similar mechanisms to those seen in in vitro reactions is expected, given that the yields of these adducts were high in the latter. Using site-directed mutagenesis, we recently showed that all three p-BQ adducts are highly mutagenic in S. cerevisiae by predominantly causing deletion mutations.…”