The ring closure was accomplished by dissolving either the 6-amino-5-forn1amido-2, 4- dihydroxypyriini-dine 1-N-oxide (X) or the 5, g-dianiine V in hot formic acid and adding acetic anhydride. The xanthine 3-N-oxide (XI) obtained was slowly reduced to xanthine in the presence of very active Raney nickel but unreduced N-oxide was still present.
