Pteridines, LXXXVIII. Oxidations and Reactions of 2- and 4-Thiolumazine Derivatives. Synthesis and Properties of Pteridine-Sulfinates and -sulfonates
Summary Selective oxidations of 2-thiolumazines (10-12) by H20 2 and KMn04 respectively in basic medium led to the corresponding stable pteridin-4-one-2-sulfinates (13-15) and -sulfonates (16-18), which can be isolated in the form of their potassium salts. On oxidation of 6,7-diphenyl-2-thiolumazine (12) with 1 equivalent of H20 2 resulted the 6,7-diphenyl-pteridin-4-one-2-sulfenate (22), which is regarded as an intermediate in the formation of the sulfinates. Characterization was done by elemental analysis, pKa determination, and UV-, IR- and IH-NMR-spectra.Acid and base hydrolyse the sulfinate and sulfonate groups to the 2-hydroxy derivative. Treatment of the pteridin-4-one-2-sulfinate with strong anhydrous acids such as formic acid or sulfuric acid affects S02 elimination to the corresponding 2-H-pteridin-4-one (19-21).The oxidative desulfurization of 2-thiolumazines can be achieved directly with H20 2 and m-chloroperbenzoic acid in formic acid. Analogously nucleophilic displacement reactions of the 2-thione group proceeded under mild conditions by H20 2 oxidation in the presence of various amines to give the corresponding pterin derivatives (25.-;-32, 36-39). 6,7-Diphenyl-4-thiolumazine (44) shows similar reactions on oxidation in the presence of amines (43, 54), but the corresponding 4-sulfinate and sulfonate are too unstable in this series to be isolated. S02 elimination does not take place since hydrolysis is the preferred reaction mode.