Synthesis and Biological Activity of Some New N1-(4-oxoquinolin-6-yl) amidrazones

Background: Oriented research towards discovery of new antimicrobial agents continues as several microbes develop resistance to currently approved drugs. A selected set of N1-(1-ethyl-4-oxoquinolin- 6-yl)amidrazone-3-carboxylates incorporating N-piperazines or related congeners have been synthesized via interaction of the particular hydrazonoyl chloride, derived from 6-amino-1-ethyl-4-oxoqinoline-3-carboxylate, with the appropriate sec-cyclic amine. Methods: The in vitro antibacterial activity screening of the synthetic compounds was performed against Gram negative Escherichia coli and Gram positive Staphylococcus aureus species. The screening test was performed using Müller Hinton Agar and Müller Hinton Broth medium. The bacterial inoculum turbidity was determined using a 0.5 McFarland standard tube to get 105 cells/ml of bacterial concentration. Bacterial cultures were grown overnight using blood agar medium prior to incubation with the synthetic compounds. 10 mg of each compound was dissolved in 1 ml of dimethyl sulfoxide (DMSO). Results: Compounds having a morpholine appendage, N-ethyl-, N-formyl-, and N-(4-methoxyphenyl)-piperazine residues showed moderate in vitro antibacterial activity against S. aureus (MIC = 10 μg/mL). Higher activity against E. coli was displayed by the morpholino, N-formyl-, and N-(4-methoxyphenyl)piperazine derivatives (MIC = 1 μg/mL), whilst the compound incorporating N-(4-fluorophenyl)piperazin-1-yl grouping exhibited the highest activity with MIC = 0.1 μg/mL. Conclusion: A selected set of quinolone-amidrazone hybrid derivatives were synthesized and tested against Gram negative E. coli and Gram positive S. aureus species. Those hybrids incorporating morpholine, N-(formyl)piperazinyl, N-(4- methoxyphenyl)piperazinyl and N-(4-fluoropheny)piperazinyl moieties exhibited the highest activity (MIC = 1-0.1 μg/mL).