3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone sodium salt (MDL 427): a new antiallergic agent.

Syntheses for 3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone sodium salt monohydrate (9; MDL 427) and the related formamido compound, 2-(formylamino)-N-1H-tetrazol-5-ylbenzamide (10), are described. Both compounds are active in the rat passive cutaneous anaphylaxis and passive peritoneal anaphylaxis tests. A 94:6 equilibrium mixture of 9 and ionized 10, respectively, forms in aqueous buffer systems at a pH-dependent rate. In addition, analogues of 3-(1H-tetrazol-5-yl)-4(3H)-quinazolinone (8) bearing substituents on the benzene ring, substituents at the 2-position, and heteroaryl groups at the 3-position other than tetrazole were prepared. These analogue sets demonstrated that an accessible electrophilic center and an acidic functionality were requirements for good antiallergic activity.