1-Azinyl-1′-Alkenylferrocenes with Anticholinesterase, Antioxidant, and Antiaggregating Activities as Multifunctional Agents for Potential Treatment of Alzheimer’s Disease

<b>Background/Objectives</b>: This study focused on synthesizing novel alkenyl derivatives of azinylferrocenes and evaluating their potential as Alzheimer's disease (AD) therapeutics. <b>Methods</b>: 1-Azinyl-1'-acetylferrocenes were obtained by regioselective acetylation of azinylferrocenes, followed by the Wittig reaction or reduction of 1-azinyl-1'-acetylferrocenes and subsequent dehydration of the resulting alcohols. The synthesized compounds underwent the following biological activity testing relevant to AD: inhibition of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and off-target carboxylesterase (CES); antioxidant capacity (ABTS and FRAP assays); inhibition of Aβ₄₂ self-aggregation (thioflavin method); blocking AChE-induced β-amyloid aggregation (propidium displacement); and cytotoxicity in SH-SY5Y and MSC-Neu cells (MTT assay). <b>Results</b>: Quinoline and bipyridine derivatives demonstrated effective cholinesterase inhibition, especially quinoline <b>7b</b> (AChE IC₅₀ 3.32 μM; BChE IC₅₀ 3.68 μM), while acridine derivatives were poor inhibitors. Quantum chemical (QC) calculations predicted that acridine derivatives were especially prone to form stable dimers. Molecular docking into protein targets generated by an AlphaFold3 reproduction code showed that these dimers were too bulky to access enzyme active sites, yet they could bind to protein surfaces to inhibit Aβ₄₂ self-aggregation and displace propidium from the AChE peripheral anionic site. All compounds showed high antioxidant activity in ABTS and FRAP assays, with quinoline derivatives being 2-4 times more potent than Trolox. QC calculations supported these findings. Quinoline and bipyridine derivatives also exhibited low cytotoxicity and scant CES inhibition. <b>Conclusions</b>: Overall, the synthesized ferrocenes, particularly the quinoline and bipyridine derivatives, appear promising for further research as multifunctional therapeutic agents targeting AD due to their anticholinesterase, antiaggregating, and antioxidant activities combined with low toxicity.