Characterization of a deoxyguanosine adduct of tetrachlorobenzoquinone: Dichlorobenzoquinone-1,N²-etheno-2′-deoxyguanosine

Pentachlorophenol (PCP), a widespread environmental pollutant that is possibly carcinogenic to humans, is metabolically oxidized to tetrachloroquinone. DNA adducts attributable to tetrachloroquinone have been observed previously in vitro and detected in vivo. In addition, an unidentified adduct in these studies coeluted with the product of the reaction of deoxyguanosine (dG) and tetrachlorobenzoquinone (Cl₄BQ). We have synthesized, isolated, purified, and characterized the predominant adduct formed from the reaction of dG and Cl₄-BQ. The preparation of a ¹³C-labeled version of this adduct facilitated its structural characterization. On the basis of ¹H NMR, ¹³C NMR, MS, IR, UV, and cyclic voltammetry, we propose that the adduct is a dichlorobenzoquinone nucleoside in which two chlorine atoms in Cl₄BQ have been displaced by reaction at the 1- and N²-positions of dG. The ¹H and ¹³C NMR chemical shifts are consistent with the dichlorobenzoquinone assignment. In contrast, under standard analytical conditions, LC-MS data are consistent with a reduced hydroquinone structure, similar to what may be expected based on results from other chloroquinones. Data from the present study indicate that this reduction could be occurring in the electrospray ionization source and that the initial product of the reaction of dG and Cl₄BQ is a dichlorobenzoquinone. The results of this study contribute to the hypothesis that direct reactions between chlorophenols and DNA may play a role in the toxic effects of chlorophenols and indicate a potential difference in reactivity and biological influence between PCP and other less substituted chlorophenols or phenols.