Synthesis and pharmacological investigation of novel 1-alkyl-4-(4-substituted aryl/heteroaryl)-1,2,4-triazolo [4,3- a] quinazolin-5 (4H)-ones as a new class of H1-antihistaminic agents

A series of novel 1-alkyl-4-(4-substituted aryl/heteroaryl)- 1,2,4-triazolo 4,3-a] quinazolin-5(4H)-ones were synthesized by the cyclization of 2-hydrazino-3-(4-subst. aryl/heteroaryl) quinazolin-4(3H)-one with various carbon donors. The starting material, 2-hydrazino-3-(4-subst. aryl/heteroaryl) quinazolin-4(3H)-one, was synthesized from 4-subst. arylamine/ heteroarylamine by a novel innovative route. When tested for their in vivo Hi-antihistaminic activity on conscious guinea pigs, all the test compounds protected the animals from histamine induced bronchospasm significantly, whereby the compound 1-methyl-4-(2-py-ridyl)-1,2,4-triazolo4,3-a] quinazolin-5(4H)-one (II) was found to be more potent (percent protection 71.43 %) when compared to the reference standard, chlorpheniramine maleate (percent protection 71 %). Compound II showed negligible sedation (8 %) when compared to chlorpheniramine maleate (25 %). Hence it could serve as prototype molecule for further development as a new class of H1-antihistamines.