Studies on Xanthine Derivatives. II. : Synthesis of 1, 2, 3, 7-Tetrahydro-6H-purin-6-ones from Xanthine Hydrolyzates

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Intramolecular cyclization of caffeidine homologues (2a and 2b) in the presence of ethanolic hydrogen chloride gave 9-oxo-1H-pyrrolo[1, 2-α]purine (4a) and 11-oxo-1H-azepino[1, 2-α]purine (4b) derivatives, both containing a 1, 2, 3, 7-tetrahydro-6H-purin-6-one ring system. Purine ring system compounds, 2-monosubstituted (7) and 2, 2, -disubstituted (8) 1, 2, 3, 7-tetrahydro-6H-purin-6-ones, were synthesized by intermolecular cyclization between caffeidine and aldehydes (5) or ketones (6) in the presence of acid catalysts. Pyrolysis of 4, 7, 8, 9, 9a, 11-hexahydro-1, 4, 9a-trimethyl-5, 11-dioxo-1H, 5H-imidazo[4, 5-f]pyrrolo[2, 1-b][1, 3, 5]-oxadiazocine hydrochloride (9·HCl) derived from a urea derivative (3a) afforded 4a and 1, 4-dimethyl-4, 5-dihydro-5, 7-dioxo-1H, 7H-imidazo[4, 5-d][1, 3]oxazine (11). Many of these compounds (4, 7 and 8) showed relaxing activity against KCl-induced contraction of arterial strips isolated from the rabbit mesenterium, and potent activity was observed in the case of 71.