Synthesis and Bronchodilator Studies of Some Novel 6-Alkyl/Aryl-1,2,4-Triazino[4,3-c]Quinazolines

A series of alkyl- and aryl-1,2,4-triazino[4,3-c]quinazolines (5a-h and 8a-h) were synthesized and characterized. The title compounds were evaluated for their in vivo bronchodilator activity on guinea pigs. All the test compounds exhibited good protection against histamine-induced bronchospasm. The structure-activity relationships based on the results obtained for these series were studied. Incorporation of an aryl ring with halo substitution to the theophylline bioisostere increases its potency. Among the compounds tested, 5b was found to be the most potent with 88.7% protection against histamine-induced bronchospasm compared to the standard compound aminophylline (87.8%).