STUDIES ON CARDIOTONIC AGENTS .6. SYNTHESIS OF NOVEL 4,5-DIHYDRO-3(2H)-PYRIDAZINONE DERIVATIVES CARRYING SOME BENZOHETEROCYCLES AT THE 6-POSITION

Several benzothiazolyl, imidazobenzothiazolyl, benzothienyl, benzothienopyrimidinyl and quinazolinyl 4,5-dihydro-3(2H)-pyridazinones were synthesized and examined for cardiotonic activity in anesthetized dogs after i.v. administration. Among them, 4-methylamino-7-(2,3,4,5-tetrahydro-5-methyl-3-oxo-6-pyridazinyl)quinazoline (36) showed potent and long-lasting inotropic activity (relative potency = 2.11, milrinone = 1). The activity of 36 was more potent that indolidan (2) (relative potency = 1.53) which is one of the most potent inotropic agents to date.