Synthesis of some substituted quinazolinediones as potential inhibitors of smooth muscle contraction.

3-Substituted 2,4(1H,3H)-quinazolinediones were prepared from the corresponding N-substituted 2-aminobenzamides by treatment with ethyl chloroformate and KOH in ethanol. Also, a series of 3-substituted and 1-methyl-3-substituted 2,4(1H,3H)-quinazolinediones were synthesized by the reaction of 1-methyl-1,4-dihydro- and 1,4-dihydro-2,4-dioxo-3(2H)-quinazolineacetic acid with the corresponding N-substituted piperazines. The 13C NMR spectra and mass spectra of the compounds were measured and signals were assigned. Some of the compounds showed inhibitory action on contractile function of smooth muscle.