Synthesis, characterization, and biological evaluation of 2-(4'-bromo[1,1'-biphenyl]-4-yl)-1H-benzo[d]imidazole derivatives

A series of novel N-functionalized derivatives of 2-(4′-bromo-[1,1′-biphenyl]-4-yl)-1H-benzo[d]imidazole (KN1-KN9) were synthesized by efficient N-substitution reactions, and their antimicrobial and cytotoxic activities were evaluated. The functionalization reactions proceeded smoothly under optimized conditions, affording the target compounds in good to excellent yields (69-81%). Structures of the synthesized compounds were confirmed using FT-IR, 1H NMR, 13C NMR, and high-resolution mass spectrometry (HRMS). The FT-IR spectra exhibited characteristic absorption bands corresponding to C=N and aromatic skeletal vibrations, while the 1H NMR spectra showed signals in the aromatic region. 13C NMR spectra further supported the proposed structures through characteristic aromatic and heteroaromatic carbon resonances, and HRMS analysis confirmed the expected molecular masses. The antimicrobial activity of the KN1-KN9 compounds was evaluated against Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), and fungal strains (Candida albicans and Saccharomyces cerevisiae) using the agar well diffusion method. Among the derivatives tested, KN7 exhibited the highest antibacterial activity against S. aureus with an inhibition zone of 20 mm and a MIC value of 31.25 µg/mL, comparable to chloramphenicol. KN1 and KN9 also showed notable activity against E. coli. Cytotoxic activity was assessed using the brine shrimp lethality assay. Several derivatives showed significant toxicity toward Artemia salina nauplii, with LD50 values ranging from 15.50 to 85.00 ppm. In particular, KN1 and KN7 exhibited the most pronounced cytotoxic effects. Preliminary structure-activity relationship analysis suggests that electron-withdrawing and lipophilic substituents enhance biological activity. As a result, these findings highlight the potential of biphenyl-substituted benzimidazole derivatives as promising scaffolds for the development of new antimicrobial and cytotoxic agents.