The SO4-.-induced oxidation of 2'-deoxyuridine-5'-phosphate, uridine-5'-phosphate and thymidine-5'-phosphate. An ESR study in aqueous solution.

Reactions of photolytically generated SO4-. with 2'-deoxyuridine-5'-phosphate (5'-dUMP), uridine-5'-phosphate (5'-UMP) and thymidine-5'-phosphate (5'-dTUMP) were studied by ESR spectroscopy in aqueous solution under anoxic conditions. From 5'-dUMP and 5'-UMP the 5',5-cyclic phosphate-6-yl radicals 10 and 11 were generated (pH 2-11) whereas from 5'-dTMP at pH 3-8 the 5,6-dihydro-6-hydroxy-5-yl radical 14 and at pH 7-11 the 5-methylene-2'-deoxyuridine-5'-phosphate radical 15 was produced. In the experiments with 5'-UMP in addition to radical 11 the signals of sugar radicals 12 and 13 were detected. It is assumed that the base radical cations act as intermediates in the SO4-.-induced radical reactions. The 5'-phosphate group adds intramolecularly to the C(5)-C(6) bond of the uraclilyl radical cation whereas the thymidyl radical cation of 5'-dTMP reacts with H2O at pH less than 8 to yield the 6-OH-5-yl adduct 14 and deprotonates at pH greater than 7 thus forming the allyl-type radical 15. In 5'-UMP transfer of the radical site from the base to the sugar moiety competes with intramolecular phosphate addition.