Design and Synthesis of 1-Substituted-4-(4-Nitrophenyl)-[1,2,4]triazolo[4,3- a ]quinazolin-5(4 H )-ones as a New Class of Antihistaminic Agents

Some new 1-substituted-4-(4-nitrophenyl)-[1,2,4]triazolo[4,3-a]quinazolin-5(4H)-ones were synthesized and screened for their H1-antihistaminic activity. The structures of the newly synthesized compounds were confirmed by IR, 1H NMR, and mass spectral data and purity of the compounds was determined by elemental analysis. Antihistaminic activity of synthesized compounds was determined by the protection against histamine-induced bronchospasm on conscious guinea pigs. Percentage protection data showed that all title compounds of the series show significant protection in the range of 68–71.56% when compared to reference drug chlorpheniramine maleate (70.17%). The sedative properties of the compounds were also evaluated and found to be negligible when compared to chlorpheniramine maleate.