Design, synthesis and H1-antihistaminic activity of novel 1-substituted-4-(3-chlorophenyl)-[1,2,4] triazolo [4,3-a] quinazolin-5(4H)-ones

In the present study a series of 1-substituted-4-(3-chlorophenyl)-[1,2,4] triazolo [4,3-a] quinazolin-5(4H)-ones were synthesized and screened for their H1-antihistaminic activity. The synthesized compounds were characterized by IR, 1H-NMR, mass spectral data and purity of the compounds was determined by elemental analysis. Antihistaminic activity of the title compounds was evaluated by histamine induced bronchoconstriction method in guinea pigs. Among the series, 4-(3-chlorophenyl)-1-methyl-[1,2,4]triazolo[4,3-a]quinazolin-5(4H)-one (S5) was the most potent with the percentage protection of 69.65% and its potency is comparable to the reference drug chlorpheniramine maleate (70.09% protection). Interestingly the sedative property of compound S5 was found to be negligible (5.36%) when compared to chlorpheniramine maleate (34.92%).