Bronchodilation and structure-activity relationship studies on new 6-substituted benzimidazo[1,2-c]quinazolines

Two series of 6-substituted benzimidazo[1,2-c]quinazolines (Ia-p and IIa-l) have been synthesized and characterized. The compounds were evaluated for their bronchodilator activity, in vitro and in vivo. All the test compounds exhibited good activity both in vivo and in vitro methods. The structure-activity relationships based on the results obtained for these series have also been studied. In the 6-alkyl substituted compounds II, a longer alkyl chain and a 4-substitution by an electron-withdrawing group in compounds I, showed more activity. The presence of halogens altered the biological activity in both series. Among the compounds tested, 10-iodo-6-(n-propyl)-benzimidazol[1,2-c]quinazoline (II) was found to be the most potent (% protection = 75%; relative activity = 1.1).