Design and synthesis of 3-(4-chlorophenyl)-2-(2-(4-substituted)-2-oxoethylthio)quinazolin-4(3H)-one as antihistamine agents

A series of novel 3-(4-chlorophenyl)-2-(2-(4-substituted)-2-oxoethylthio)quinazolin-4(3H)-one was synthesized by the reaction of 2-(3-(4-chlorophenyl)-4-oxo-3,4-dihydroquinazolin-2-ylthio)acetyl chloride with various amines. The starting material, (3-(4-chlorophenyl)-4-oxo-3,4-dihydroquinazolin-2-ylthio)acetyl chloride was synthesized from 4-chloroaniline by a multistep synthesis. All the title compounds were tested for their in vivo H₁-antihistaminic activity on conscious guinea pigs at the dose level of 10 mg/kg using chlorpheniramine maleate as the reference standard. The results of the biological activity indicate that the test compounds protected the animals from histamine-induced bronchospasm significantly. Compound 3-(4-chlorophenyl)-2-(2-(4-methylpiperazin-1-yl)-2-oxoethylthio)quinazolin-4(3H)-one (1) emerged as the most potent compound of the series (71.13 % protection) when compared to the reference standard chlorpheniramine maleate (70.09 % protection). Interestingly, compound A1 shows negligible sedation (12 %) compared to chlorpheniramine maleate (32 %). Therefore, compound A1 can serve as the lead molecule for further development.