.beta.-Purine 120-73-0 1H-Purine 3,5,7-Triazaindole 6H-Imidazo[4,5-d]pyrimidine 7H-Imidazo[4,5-d]pyrimidine 7H-Purine 9H-Purine Imidazo[4,5-d]pyrimidine Isopurine NSC 753 NSC753 Purine WLN: T56 BM DN FN HNJ X 128