Influence of the pH in the OH Radical Attack on the Pyrimidic Ring

Abstract

Abstract The attack of OH radical on pyrimidic ring preferential­ ly took place at position 5 at neutral pH and at position 6 at low acidic pH. The trans isomers were always the major products. These conclusions arose from studies involving comparison with synthetic peroxides: c£s-6-hydroperoxy-5-hydroxy-5,6-dihydrothymine (1), as-5-hydroperoxy-6-hydro-xy-5,6-dihydrothymine (2) , frans-6-hydroperoxy-5-hydroxy-5.6-dhydrothymine (3) and ?rans-5-hydroperoxy-6-hydroxy-5.6-dihydrothymine (4) . The NMR coupling constants of the OH-6 proton with H-6 allowed us to assign unambiguously the structures of these peroxides in agreement with 18O mass spectrometry results. G radiolytic values and NMR data are given