8-Mercapto-6-thiotheophylline

6,7-Dihydro-1,3-dimethyl-8-mercapto-6-thioxo-1H-purin-2(3H)-one

6,7,8,9-Tetrahydro-1,3-dimethyl-6,8-dithioxo-1H-purin-2(3H)-one