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 <b>16e</b> (IC₅₀ = 0.10 μM for AChE, 0.043 μM for BuChE) and <b>16h</b> (IC₅₀ = 0.21 μM for AChE, 0.10 μM for BuChE). These compounds also exhibited potent inhibition of self-induced Aβ_1-42 aggregation (<b>16e</b>: 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.