imidazopyrimidinones and other diazaheterocyclopyrimidinones having an additional fused imidazole or triazole ring have utility as bronchodilators , mediator release inhibitors , phosphodiesterase inhibitors , and peripheral vasodilators . they are orally active and useful in the prophylaxis and treatment of asthma . a preferred compound is 4 - methyl ]- 6 , 7 - dihydro - 3h - imidazopurin - 9 - one .