The SO 4 - induced Oxidation of 2 ' - Deoxyuridine - 5 ' - phosphate , Uridine - 5 - phosphate and Thymidine - 5 - phosphate .

Reactions o f photolytically generated SOJ with 2'-deoxyuridine-5 '-phosphate (5 '-dU M P), uridine-5 '-phosphate (5 '-U M P) and thym idine-5 '-phosphate (5'-dTM P) were studied by ESR spectroscopy in aqueous solution under anoxic conditions. From 5'-dU M P and 5 '-U M P the 5',5-cyclic phosphate-6 -yl radicals 10 and 11 were generated (pH 2 -1 1 ) whereas from 5 '-dTM P at .pH 3 8 the 5,6-dihydro-6-hydroxy-5-yl radical 14 and at pH 7 -1 1 the 5-m ethylene-2 '-deoxyuridine-5 '-phosphate radical 15 was produced. In the experiments with 5 '-U M P in addition to radical 11 the signals o f sugar radicals 12 and 13 were detected. It is assum ed tha t the base radical cations act as interm ediates in the SO^-induced radical reac­ tions. The 5 '-phosphate g roup adds intram olecularly to the C (5 )-C (6 ) bond o f the uraclilyl radical cation w hereas the thym idyl radical cation o f 5 '-dTM P reacts with H 20 at pH < 8 to yield the 6-OH-5-yl adduct 14 and depro tonates a t pH > 7 thus forming the allyl-type radical 15. In 5 '-U M P transfer o f the radical site from the base to the sugar moiety com petes with in tram olecular phosphate addition.