Design, synthesis, biological evaluation, and in silico studies of imidazo[2,1-b][1,3,4]thiadiazole derivatives as cholinesterase inhibitors

In this study, a series of imidazo[2,1-b][1,3,4]thiadiazole derivatives were designed, synthesized, and evaluated as potential cholinesterase inhibitors (ChEIs) for the treatment of Alzheimer’s disease (AD). Furthermore, the antioxidant activities of these compounds were examined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay. The inhibition assay against cholinesterase (ChE) revealed that these synthesized compounds exhibited moderate inhibitory activities against both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Notably, some of the tested compounds had varying antioxidant activities. Specifically, compound 20aa (eeAChE, IC₅₀ = 0.75 μM; eqBChE, IC₅₀ = 4.11 μM; SI = 5.48) was found to be the most effective ChEI, exhibiting approximately 5-fold greater activity against AChE and 4-fold greater activity against BChE compared to galantamine. Additionally, compound 20aa also possessed antioxidant activity, with IC₅₀ value of 442.87 µM. To understand the binding mode of compound 20aa, molecular docking studies were performed, and the results indicated that compound 20aa could interact with amino acid residues in the catalytic active site (CAS) of both BChE and AChE, as well as with the peripheral anionic site (PAS) of AChE. Among them, compound 20aa showed a mixed inhibition pattern with AChE, which aligned with the results of the enzyme kinetics studies. Molecular dynamics (MD) simulation studies demonstrated the stability of the 20aa-AChE/BChE complexes. Considering its biological activity and molecular properties, compound 20aa could be a promising lead compound for the development of AD drugs.