Multifunctional Tacrine–Quinoline Hybrids as Cholinesterase Inhibitors, Aβ Aggregation Blockers, and Metal Chelators for Alzheimer’s Therapy

A novel series of multifunctional tacrine–quinoline hybrids were designed, synthesized, and evaluated as potential anti-Alzheimer’s agents. These compounds incorporate tacrine for cholinesterase’s inhibition and 8-hydroxyquinoline for metal chelation. Piperazine was selected as a linker to provide conformational flexibility and to create favorable cation–π interactions with residues in the mid-gorge region of AChE, enhancing dual-site binding with AChE to inhibit Aβ aggregation. In vitro studies demonstrated submicromolar inhibitory activity toward both AChE and BuChE, particularly for compounds 16e (IC50 = 0.10 μM for AChE, 0.043 μM for BuChE) and 16h (IC50 = 0.21 μM for AChE, 0.10 μM for BuChE). These compounds also exhibited potent inhibition of self-induced Aβ1–42 aggregation (16e: 80.5% ± 4.4%, 16h: 93.2% ± 3.9% at 20 μM). Kinetic analyses revealed mixed-type inhibition, suggesting dual binding to both CAS and PAS of AChE. UV–vis spectrometry confirmed the chelation of Cu2+ and Zn2+ ions by the 8-hydroxyquinoline moiety. These findings highlight the tacrine–quinoline scaffold as a promising platform for the discovery of a multitarget-directed anti-AD drug.