ESR of Spin-Trapped Radicals in Aqueous Solutions of Dihydropyrimidine Bases

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Abstract
Reactions of hydroxyl radicals with several dihydropyrimidine base derivatives in aqueous solutions have been investigated by spin-trapping and ESR spectroscopy. Hydroxyl radicals were generated by the UV photolysis of H2O2, and tertiary nitrosobutane was used as the spintrapping reagent. Dihydro derivatives of uracil, 6-methyluracil, 1-methyluracil, 1-ethyluracil, 1-methylcytosine, 5-methylcytosine, thymine and orotic acid were investigated. The predominant reaction in all cases was abstraction of H atoms bound to the C(6) position. To a lesser extent H-abstraction took place from the methyl groups attached to the N(1), C(5) and C(6) positions. For dihydro-1-ethyluracil, H atoms were abstracted from carbon atoms of the ethyl group. Radicals produced by H-abstraction from the C(5) or C(6) positions of the dihydropyrimidines are equivalent to those formed by H atom addition to the C(5).sbd.C(6) double bonds of the corresponding pyrimidines. These results are helpful in distinguishing between spin-trapped radicals formed by H or OH addition to the C(5).sbd.C(6) double bond of pyrimidines of .gamma.-irradiated aqueous solutions.

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