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.