Heterocyclic compounds containing purine ring systems with oxygen, sulfur 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
Heterocyclic compounds containing purine ring systems with oxygen, sulfur 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