Synthesis, In Vivo and In Silico Evaluation of Analgesic, Anti-Inflammatory and Antidiarrheal Activities of Benzimidazole Derivatives

A number of benzimidazole derivatives (3a–3d) were synthesized in high yields (66–94%) by condensing carboxylic acid and aromatic diamine, namely o-phenylenediamine, in the presence of concentrated HCl and evaluated for their analgesic, anti-inflammatory, and antidiarrheal actions in both in vivo and in silico methods. Among the synthesized compounds, compounds 3d and 3b showed the most potent analgesic (62.3% and 58.98% writhing inhibition respectively), and compound 3c and 3d showed anti-inflammatory activity in 1st hour to 4th hour (76.36, 76.60, 71.43, 73.29, and 80.61, 88.30, 80.52, and 66.07% inhibition of paw edema, respectively) compared to standard diclofenac sodium (92.54% writhing inhibition and 56.97, 78.72, 90.91, and 99.64% inhibition of paw edema). Compound 3a showed the most significant antidiarrheal activity (66.67% inhibition of defecation) compared to standard loperamide (75.0%) at 50 mg/kg dose. In molecular docking analysis, compound 3d showed the highest binding affinity toward COX-1 and COX-2 (−8.7 and −8.9 kcal/mol respectively) compared to standard diclofenac sodium (−8.2 and −8.4 kcal/mol), which is consistent with the in vivo result. Molecular docking thus revealed that analgesic and anti-inflammatory activity is likely to be related to inhibition of COX enzymes, with the structure of the substituents having an effect on both binding affinity and selectivity. On the other hand, compounds 3c and 3d showed the highest binding (−9.1 and −10.2 kcal/mol) compared to loperamide (−8.4 kcal/mol) against kappa opioid receptor (KOR). Since compound 3a did not show much affinity toward KOR, suggesting a potential different target and/or mechanism. So, the synthesized benzimidazole derivatives could act as potential leads for developing new analgesic and antidiarrheal molecules.