Two series of naphthoquinone and anthraquinone derivatives decorated with an aromatic/heteroaromatic chain have been synthesized and evaluated as potential promiscuous agents capable of targeting different factors playing a key role in Alzheimer's disease (AD) pathogenesis. On the basis of the in vitro biological profiling, most of them exhibited a significant ability to inhibit amyloid aggregation, PHF6 tau sequence aggregation, acetylcholinesterase (AChE), and monoamine oxidase (MAO) B. In particular, naphthoquinone 2 resulted as one of the best performing multitarget-directed ligand (MTDL) experiencing a high potency profile in inhibiting β-amyloid (Aβ40) aggregation (IC50 = 3.2 μM), PHF6 tau fragment (91% at 10 μM), AChE enzyme (IC50 = 9.2 μM) jointly with a remarkable inhibitory activity against MAO B (IC50 = 7.7 nM). Molecular modeling studies explained the structure-activity relationship (SAR) around the binding modes of representative compound 2 in complex with hMAO B and hAChE enzymes, revealing inhibitor/protein key contacts and the likely molecular rationale for enzyme selectivity. Compound 2 was also demonstrated to be a strong inhibitor of Aβ42 aggregation, with potency comparable to quercetin. Accordingly, atomic force microscopy (AFM) revealed that the most promising naphthoquinones 2 and 5 and anthraquinones 11 and 12 were able to impair Aβ42 fibrillation, deconstructing the morphologies of its fibrillar aggregates. Moreover, the same compounds exerted a moderate neuroprotective effect against Aβ42 toxicity in primary cultures of cerebellar granule cells. Therefore, our findings demonstrate that these molecules may represent valuable chemotypes toward the development of promising candidates for AD therapy.
Keywords: AChE and BChE inhibition; Aβ and Tau aggregation inhibition; MAO inhibition; Naphthoquinone and anthraquinone derivatives; multitarget-directed ligands (MTDLs).