Synthesis of 4-butyl-1-substituted-4 H-[1,2,4]triazolo[4,3- a]quinazolin-5-ones as new class of H 1-antihistaminic agents

Abstract

A series of novel 4-butyl-1-substituted-4 H-[1,2,4]triazolo [4,3- a] quinazolin-5-ones were synthesized by the cyclization of 3-butyl-2-hydrazino-3 H-quinazolin-4-one with various one carbon donors. The starting material 3-butyl-2-hydrazino-3 H-quinazolin-4-one was synthesized from butyl amine by a new innovative route. When tested for their in vivo H 1-antihistaminic activity on conscious guinea pigs, all the test compounds protected the animals from histamine induced bronchospasm significantly. Compound 4-butyl-1-methyl-4 H-[1,2,4]triazolo[4,3- a] quinazolin-5-one ( II) emerged as the most active compound of the series and it is equipotent (71.91% protection) when compared to the reference standard chlorpheniramine maleate (71% protection). Compound II show negligible sedation (9%) when compared to chlorpheniramine maleate (30%).