Pyridazine analogues of biologically active compounds. Part 5: Novel potential cardiotonics of the amrinone type.

Preparation of a series of novel pyridazine derivatives structurally related to bipyridine cardiotonics, starting from 4-methylpyridazine or 4-acetylpyridazine, respectively, is described. As observed with compounds 8, 11 and 16, an enhancement of in vitro cardiotonic activity is associated with the replacement of one or both pyridine subunit(s) in amrinone or milrinone by a 1,2-diazine system.