A novel 3-amino-4(3H)-quinazolinone was synthesized via two routes. The first route involved interaction of 2,3-pyridine dicarboxylic anhydride with anthranilic acid in acetic acid under reflux to give the amide derivative which was subjected to cyclodehydration and treatment with hydrazine hydrate. The second route involved preparation of amide by treatment of 2,3-pyridine dicarboxylic anhydride with methyl anthranilate in glacial acetic acid under reflux, then treated with hydrazine hydrate. Treatment of 3-amino-4(3H)-quinazolinone with isocyanate, isothiocyanate, ethyl chloroacetate and diethyl malonate gave urea, thiourea, thiazole and pyrimidine derivatives, respectively. In addition, some bisquinazolines were synthesized. Antimicrobial activities of some selected compounds were screened.