Design, Synthesis and Antibacterial Evaluation of (E)-4-methyl-N'-(1-phenylethylidene)tetrazolo[1,5-a] quinoxaline-8-sulfonohydrazide Derivatives

Abstract

Quinoxaline derivatives are of continuing interest because of their diverse biological properties and their suitability for structural modification. This study synthesised a series of (E)-4-methyl-N'-(1-phenylethylidene)tetrazolo[1,5-a]quinoxaline-8-sulfonohydrazide derivatives and evaluated their antibacterial activity against selected clinical bacterial isolates. The derivatives were prepared by condensation of 4-methyltetrazolo[1,5-a]quinoxaline-8-sulfonohydrazide with substituted aromatic ketones and were characterised using Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and carbon-13 nuclear magnetic resonance spectroscopy. Antibacterial activity was assessed by the agar-well diffusion method, followed by determination of the minimum inhibitory concentration and minimum bactericidal concentration. Streptomycin and tetracycline served as positive controls, and the agar-well diffusion experiments were performed in triplicate. Compounds 1a–1h showed measurable antibacterial activity against all bacterial isolates tested. The recorded inhibition zones for the synthesised compounds ranged from 13 to 48 mm, whereas the standard antibiotics produced inhibition zones of 15–25 mm. The minimum inhibitory and bactericidal concentrations varied among compounds and organisms, with the lowest recorded values being 78.1 µg/mL. Spectroscopic findings supported formation of the intended hydrazone derivatives, while differences in antibacterial responses indicated that aromatic substitution influenced activity within the series. Overall, the synthesised tetrazoloquinoxaline sulfonohydrazide derivatives demonstrated in vitro antibacterial activity and provide a basis for further structure–activity evaluation and optimisation of this compound class.