8-[(2-Pyridylmethyl)thio]-6-thiotheophylline

8-[(2-Pyridylmethyl)thio]-3,7-dihydro-1,3-dimethyl-6-thio-1H-purin-2-one

6,7-Dihydro-1,3-dimethyl-8-[(pyridin-2-yl)methylthio]-6-thioxo-1H-purin-2(3H)-one