Development and Antimicrobial Assessment of Structurally Modified Benzimidazole Derivatives

Background: Antimicrobial resistance (AMR) has emerged as a major global health challenge, reducing the effectiveness of existing antibiotics and creating an urgent need for novel antimicrobial agents. Benzimidazole is a privileged heterocyclic scaffold known for its structural versatility and broad-spectrum biological activities. This study aimed to design, synthesize, and evaluate benzimidazole-acetohydrazide Schiff base derivatives as potential antimicrobial agents. Methodology: Fifteen benzimidazole-based acetohydrazide Schiff base derivatives (1–15) were synthesized from 2-mercaptobenzimidazole through nucleophilic substitution, hydrazinolysis, and condensation with substituted aromatic aldehydes. Structural characterization was performed using IR, ¹H NMR, ¹3C NMR, and mass spectrometry. Antibacterial activity was evaluated against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa using the tube dilution method, with cefadroxil as the reference drug. A 3D-QSAR CoMFA model was also developed to investigate structure–activity relationships. Results: Several synthesized derivatives exhibited potent antibacterial activity with minimum inhibitory concentration (MIC) values superior to cefadroxil. Compound 10 demonstrated the highest activity against S. aureus, E. faecalis, and E. coli (MIC = 0. 032 µM/mL) and strong activity against P. aeruginosa (MIC = 0. 016 µM/mL). Compounds 5 and 11 also showed excellent anti-Pseudomonas activity. Structure–activity relationship analysis revealed that para-substituted electron-withdrawing groups, particularly bromine, and heteroaromatic substituents significantly enhanced antimicrobial efficacy. The CoMFA model showed excellent predictive performance, with electrostatic fields contributing 70. 9% to biological activity. Conclusion: Benzimidazole-acetohydrazide Schiff base derivatives exhibited promising antibacterial activity and may serve as valuable lead compounds for developing new therapies against multidrug-resistant bacterial infections.