6-Sulfinyl Derivatives of Xanthines

6-Thiopurines are oxidized by hydrogen peroxide or by perbenzoic acid to 6-sulfinylpurines. In general, these compounds are unstable and only a number of theophylline derivatives have been obtained in pure form. In this series only the isomers in which the 6-sulfinyl group is directed toward 7-NH are formed, since they are stabilized by an intramolecular hydrogen bridge. Their structure has been derived from dipole moments and from the chemical shift of the 1-methyl substituent. The 2-thiocarbonyl group in 2-thiotheophyllines is not attacked by the oxidants used. The latter convert 6-selenoxanthines directly into the corresponding xanthines.