Abstract
The 8‐oxopurine nucleosides 2′,3′,5′‐tri‐O‐acetyl‐8‐oxo‐7,8‐dihydroguanosine (OG) and 2′,3′,5′‐tri‐O‐acetyl‐ribosyluric acid (RU) were studied for their ability to mediate the photochemical (λ > 300 nm) reversion of cyclobutane pyrimidine dimers to their parent pyrimidines thymine and uracil. The bimolecular reactions of these monomers proceeded at very slow rates compared with recently published work using oligonucleotide contexts; nevertheless, it was possible to make comparisons between the efficacy of OG and RU as photocatalysts as a function of pH. Although RU has a lower redox potential and anionic character, it was only equivalent to OG in facilitating thymine dimer photorepair over a broad pH range. Only OG showed pH‐dependent behavior with higher activity at pH 8–9 where the base becomes deprotonated. Despite the overall low activity of OG and RU, the results are instructive with respect to a comparison of the two 8‐oxopurines, and support the hypothesis that 8‐oxopurine nucleosides may have played primordial roles as precursors to modern‐day flavins in redox reactions of the RNA world. Copyright © 2012 John Wiley & Sons, Ltd.
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