Abstract
As an extension of the work on the permanganate oxidation and the oxygen-mediated bisulfite reaction of 4-thiouridine, the reactions of 2-thiouracil were studied. On treatment with a stoichiometric amount of permanganate at pH 7 and 0°, 2-thiouracil yielded uracil-2-sulfonate. The sulfonate was susceptible to hydrolysis with weak acid but was stable in alkali. Kinetic studies of the acid hydrolysis were carried out. 2-Thiouridine also underwent a rapid oxidation on treatment with permanganate under similar conditions. Uridine and a small amount of uracil were detected as the products of the reaction of the nucleoside, suggesting that the intermediate uridine-2-sulfonate is more susceptible to hydrolysis compared with uracil-2-sulfonate. Treatment of 2-thiouracil with dilute bisulfite at pH 7 and room temperature under oxygen-bubbling resulted in quantitative formation of uracil-2-sulfonate. The mechanism of the reaction involves action of the free radicals generated during the autoxidation of bisulfite, a mechanism already had been described in the bisulfite reaction with 4-thiouridine.Oxygen-mediated bisulfite reaction with 2-thiouridine was shown to be complex, yielding not only uridine but also other products including an appreciable amount of uracil.
