Cardiotonic agents. 4. Synthesis and biological evaluation of N-substituted 2,4,4a,5-tetrahydro-3H-indeno[1,2-c]pyridazin-3-ones: rigid structures derived from CI-930 and analogues.

Several N-substituted 3H-indeno[1,2-c]pyridazinones (1-23) and a benzo[h]cinnolinone (24), which were designed as rigid structural modifications of 5-alkyl-4,5-dihydro-6-[4-N-substituted phenyl]-3(2H)-pyridazinones (ib-d), were synthesized and evaluated for positive inotropic activity. Most of these tricyclic pyridazinones (1-11, 14-15, 22-23) demonstrated potent positive inotropic activity comparable to the corresponding phenylpyridazinones related to I.