Cardiotonic agents. 3. Synthesis and biological activity of novel 6-(substituted 1H-imidazol-4(5)-yl)-3(2H)-pyridazinones

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Abstract
Several 6-(substituted 1H-imidazol-4(5)-yl-3(2H)-pyridazinones) were synthesized and evaluated for positive inotropic activity. The 1H-imidazol-4-yl regioisomers 4,5-dihydro-6-(1-methyl-2-phenyl-1H-imidazol-4-yl)-3(2H)-pyridazinone (25a) and 6-(1-methyl-2-phenyl-1H-imidazol-4-yl)-3(2H)-pyridazinone (28a) were potent positive inotropic agents. By contrast, the corresponding 1H-imidazol-5-yl regioisomers 25b and 28b were only weak positive inotropic agents. Compounds 25a and 28a were also potent inhibitors of cardiac phosphodiesterase fraction III.