Synthesis and Evaluation of 2-Mercaptobenzimidazole Mannich Base Derivatives as Carbonic Anhydrase II Inhibitors

Abstract

Background: Carbonic anhydrases (CAs) are zinc-containing enzymes that catalyze the reversible conversion of carbon dioxide into bicarbonate. These enzymes play an important role in several physiological and pathological processes, including glaucoma, epilepsy, osteoporosis, and cancer. However, commonly used sulfonamide-based inhibitors often lack selectivity for specific isoforms, which can lead to unwanted side effects. The present study aimed to synthesize and investigate a series of 2-mercaptobenzimidazole-based Mannich derivatives (2a–i) as potential non-classical inhibitors of carbonic anhydrase II (CA II).

Methods: The target compounds were prepared using a reflux condensation method and characterized through FTIR and proton NMR (¹H NMR) spectroscopy. Their biological potential was assessed by evaluating antioxidant activity using the DPPH assay, inhibitory activity against CA II through in vitro analysis, and binding interactions via molecular docking studies (PDB ID: 1A42).

Results: Among the synthesized compounds, 2h, 2f, 2e, and 2g demonstrated the strongest binding affinities in docking studies, with energies ranging from −8.3 to −7.6 kcal/mol. These compounds also exhibited notable CA II inhibitory activity, with IC₅₀ values between 182.20 and 222.21 µM. In addition, compound 2f showed the most significant antioxidant activity, with an IC₅₀ value of 5.11 µM.

Conclusion: The findings suggest that Mannich base derivatives of 2-mercaptobenzimidazole may serve as promising candidates for the development of novel, non-classical inhibitors of CA II.