American Chemical Society
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Hydroxyl Radical-Induced Oxidation of a Phenolic C-Linked 2′-Deoxyguanosine Adduct Yields a Reactive Catechol

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journal contribution
posted on 2012-02-20, 00:00 authored by Aaron A. Witham, Daniel G. Beach, Wojciech Gabryelski, Richard A. Manderville
Phenolic toxins stimulate oxidative stress and generate C-linked adducts at the C8-site of 2′-deoxyguanosine (dG). We previously reported that the C-linked adduct 8-(4″-hydroxyphenyl)-dG (p-PhOH-dG) undergoes oxidation in the presence of Na2IrCl6 or horseradish peroxidase (HRP)/H2O2 to generate polymeric adducts through phenoxyl radical production [Weishar (2008) Org. Lett. 10, 1839−1842]. We now report on reaction of p-PhOH-dG with two radical-generating systems, CuII/H2O2 or FeII-EDTA/H2O2, which were utilized to study the fate of the C-linked adduct in the presence of hydroxyl radical (HO). The radical-generating systems facilitate (i) hydroxylation of the phenolic ring to afford the catechol adduct 8-(3″,4″-dihydroxyphenyl)-dG (3″,4″-DHPh-dG) and (ii) H-atom abstraction from the sugar moiety to generate the deglycosylated base p-PhOH-G. The ratios of 3″,4″-DHPh-dG to p-PhOH-G were ∼1 for CuII/H2O2 and ∼0.13 for FeII-EDTA/H2O2. The formation of 3″,4″-DHPh-dG was found to have important consequences in terms of reactivity. The catechol adduct has a lower oxidation potential than p-PhOH-dG and is sensitive to aqueous basic media, undergoing decomposition to generate a dicarboxylic acid derivative. In the presence of excess N-acetylcysteine (NAC), oxidation of 3″,4″-DHPh-dG produced mono-NAC and di-NAC conjugates. Our results imply that secondary oxidative pathways of phenolic-dG lesions are likely to contribute to toxicity.