Design, Synthesis, and Anti-Alzheimer Activity of 2,5-Disubstituted 1,3,4-Thiadiazole: Kinetic Studies, Molecular Docking, and MD Simulations

Objective: This study aims to design a small library of novel 2,5-disubstituted 1,3,4-thiadiazole derivatives and evaluate their antioxidant and acetylcholinesterase (AChE) inhibitory activities. Methods: A series of 2,5-disubstituted 1,3,4-thiadiazole derivatives were designed, synthesized via a convenient synthetic route, and assessed for their AChE inhibitory activity against electric eel AChE using Ellman’s method. Their antioxidant potential was evaluated via the DPPH free radical scavenging assay. The structures of the synthesized compounds were characterized using FT-IR, 1H, 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Molecular docking and molecular dynamics (MD) simulations were performed to identify potential AChE inhibitors. Results and Discussion: The results demonstrated that compounds (IVe), (IVj), and (IVg) exhibited significant antioxidant activity at 100 µg/mL compared to the reference standard. The AChE inhibition assay revealed that compounds (IVe), (IVj), (IVg), and (IVc) displayed potent inhibitory effects at a concentration of 0.004 M. Kinetic studies elucidated the mode of enzyme inhibition, showing that compound (IVe) exhibited a mixed-type inhibition mechanism, similar to Donepezil. Docking studies predicted moderate to strong binding affinities for all synthesized compounds (IVa–IVj) compared to the reference drug. Among them, compound (IVe) demonstrated the lowest docking energy (–10.549 kcal/mol), suggesting the highest anticholinesterase activity. MD simulations further confirmed the stable binding interactions of compound (IVe) within the active site of AChE. Conclusions: These findings suggest that compound (IVe) is a promising lead structure for the development of novel AChE inhibitors for the treatment of Alzheimer’s disease (AD).