Novel Tacrine–Benzofuran Hybrids as Potent Multitarget-Directed Ligands for the Treatment of Alzheimer’s Disease: Design, Synthesis, Biological Evaluation, and X‑ray Crystallography

Twenty-six new tacrine–benzofuran hybrids were designed, synthesized, and evaluated in vitro on key molecular targets for Alzheimer’s disease. Most hybrids exhibited good inhibitory activities on cholinesterases and β-amyloid self-aggregation. Selected compounds displayed significant inhibition of human β-secretase-1 (hBACE-1). Among the 26 hybrids, 2e showed the most interesting profile as a subnanomolar selective inhibitor of human acetylcholinesterase (hAChE) (IC50 = 0.86 nM) and a good inhibitor of both β-amyloid aggregation (hAChE- and self-induced, 61.3% and 58.4%, respectively) and hBACE-1 activity (IC50 = 1.35 μM). Kinetic studies showed that 2e acted as a slow, tight-binding, mixed-type inhibitor, while X-ray crystallographic studies highlighted the ability of 2e to induce large-scale structural changes in the active-site gorge of Torpedo californica AChE (TcAChE), with significant implications for structure-based drug design. In vivo studies confirmed that 2e significantly ameliorates performances of scopolamine-treated ICR mice. Finally, 2e administration did not exhibit significant hepatotoxicity.