Design, Synthesis and Antibacterial Evaluation of (E)-N-(3-methyl-6-nitroquinoxalin-2-yl)-4-((1-phenylethylidene) Amino) Benzenesulfonamide Derivatives

Abstract

Antibiotic resistance has increased the need to investigate new antibacterial scaffolds. This study synthesized a series of quinoxaline sulfonamide Schiff base derivatives, designated 1a–h, and evaluated their antibacterial activity against selected bacterial strains. The compounds were prepared through the reaction of 4-amino-N-(3-methylquinoxalin-2-yl)benzenesulfonamide with substituted acetophenones in ethanol in the presence of glacial acetic acid and were characterized using infrared and nuclear magnetic resonance spectroscopy. Antibacterial activity was assessed by the agar-well diffusion method, followed by determination of minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), and killing rates. Streptomycin and tetracycline were included as standard antibiotics in the diffusion, MIC, and MBC assays, while streptomycin was used in the killing-rate comparisons. The compounds produced zones of inhibition ranging from 13 to 45 mm against the bacterial isolates tested. Their MIC values ranged from 0.0781 to 0.625 mg/mL, while MBC values ranged from 0.156 to 1.25 mg/mL. The killing-rate experiments showed time- and concentration-dependent antibacterial effects. Among the synthesized derivatives, compound 1g showed the strongest overall killing-rate performance reported in the study. These findings indicate that the synthesized quinoxaline sulfonamide Schiff bases possess measurable antibacterial activity under the experimental conditions used. Further optimisation and evaluation of the active derivatives are required to assess their potential as antibacterial candidates.