C07D473/00—Heterocyclic compounds containing purine ring systems
C07D473/02—Heterocyclic compounds containing purine ring systems with oxygen, sulphur, or nitrogen atoms directly attached in positions 2 and 6
C07D473/04—Heterocyclic compounds containing purine ring systems with oxygen, sulphur, or nitrogen atoms directly attached in positions 2 and 6 two oxygen atoms
C07D473/06—Heterocyclic compounds containing purine ring systems with oxygen, sulphur, or nitrogen atoms directly attached in positions 2 and 6 two oxygen atoms with radicals containing only hydrogen and carbon atoms, attached in position 1 or 3
C07D473/08—Heterocyclic compounds containing purine ring systems with oxygen, sulphur, or nitrogen atoms directly attached in positions 2 and 6 two oxygen atoms with radicals containing only hydrogen and carbon atoms, attached in position 1 or 3 with methyl radicals in positions 1 and 3, e.g. theophylline