Synthesis and pharmacological investigation of some novel 2-phenyl-3-(substituted methyl amino) quinazolin-4(3H)-ones as H1-receptor blockers.

A series of 2-phenyl-3-(substituted methyl amino) quinazolin-4(3H)-ones were synthesized from 3-amino-2-phenyl quinazolin-4(3H)-one. Their structures were confirmed by spectral data (IR, NMR, and MS) and the purity was ascertained by microanalysis. When tested for H1-receptor blocking activity on isolated guinea pig ileum all the test compounds inhibited histamine induced contraction whereas the compounds 1 (IC50 0.59 x 10(3) ng/ml) and 5 (IC50 0.49 x 10(3) ng/ml) were found to be two fold potent when compared to standard chlorpheniramine maleate. These compounds show less sedation (compound 1 shows 4%, compound 5 shows 7%) than the standard (33%). Hence they could serve as prototype molecules for future development.