Synthesis and Antimicrobial Activities of New Pyrazolopyridazine Derivatives

Several new pryrazolo-pyridazine derivatives (4a-h) were synthesized through multi-step synthesis and evaluated for their antimicrobial activities. In the first step, 6-phenyl-2,3,4,5-tetrahydropyridazin-3-one (2) was prepared by reacting 4-(4-chlorophenyl)-4-oxobutanoic acid (1) with hydrazine hydrate. Then, aryl-aldehydes were reacted with 2 to furnish pyridazinone derivatives (3a-g). Finally, pyridazinones (3a-h) were reacted with hydrazine hydrate to furnish the title compounds (4a-h). The newly synthesized compounds were evaluated for their in vitro antibacterial and antifungal activities against six microbial strains. Compounds 4d, 4e and 4f exhibited significant antibacterial action, whereas compounds 4c and 4d showed potential antifungal activity. Compound 4d, 5-(4-Chlorophenyl)-3-(4-fluorophenyl)-3,3a,4,7-tetrahydro-2H-pyrazolo[3,4-c]pyridazine, emerged as lead compound having broad spectrum of antimicrobial action.