PHOTOCHEMISTRY OF PURINE 3-OXIDES IN HYDROXYLIC SOLVENTS

Article abstract of DOI:10.1016/0040-4020(82)87015-4

UV irradiation of the potent oncogen hypoxanthine 3-oxide in aqueoous solution induces elimination of and rearrangement of the nitrogen-bound oxygen.The extent of each reaction shows a complex variation over the pH range 0-7.The variations in quantum yield for product formation are shown to result from the presence in the neutral molecule of tautomeric species with differing photochemistries that ionize in the excited state (pK_a^* ca. 3.5) just above the protonation pK_a (1.2).The photochemical reactivity of each ionic and each tautomeric form was assigned by comparing the effect of pH changes between 0 and 11 on the quantum yields for formation of each photoproduct from hypoxanthine 3-oxide with those of two model compounds, 1-hydroxyhypoxanthine and 6-methoxypurine 3-oxide.Photoreduction of the 3-oxides occurs via the triplet state.This process has a relatively consistent low quantum yield (Φ=0.005 to 0.04) for most ionic and tautomeric forms of both purine 1-oxides and purine 3-oxides.Photorearrangement is a much more efficient process for purine 3-oxides (Φ=0.3) than for purine 1-oxides (Φ=0.04).