The synthesis, toxicity, neuroprotection, and human acetylcholinesterase (hAChE)/ human butyrylcholinesterase (hBuChE) inhibition properties of β-naphthotacrines1-14 as new drugs for Alzheimer's disease (AD) potential treatment, are reported. β-Naphthotacrines1-14 showed lower toxicity than tacrine; moreover, at the highest concentration assayed (300 μM) compounds 7, 10 and 11 displayed 2.25-2.01-fold higher cell viability than tacrine in HepG2 cells. A neuroprotective effect was observed for compounds 10 and 11 in a neuronal cortical culture exposed to a combination of oligomycin A/rotenone. An efficient and selective inhibition of hAChE, was only observed for the β-naphthotacrines bearing electron-donating substituents at the aromatic ring, β-naphthotacrine10 being the most potent (hAChE: IC50 = 0.083 ± 0.024 μM). Kinetic inhibition analysis clearly demonstrated that β-naphthotacrine10 behaves as a mixed-type inhibitor (K i2= 0.72 ± 0.06 μM) at high substrate concentrations (0.5-10 μM), while at low concentrations (0.01-0.1 μM) it behaves as a hAChE competitive inhibitor (Ki1= 0.007 ± 0.001 μM). These findings identified β-naphthotacrine10 as a potent and selective hAChE inhibitor in a nanomolar range, with toxicity lower than that of tacrine both in human hepatocytes and rat cortical neurons, with a potent neuroprotective activity and, consequently, an attractive multipotent active molecule of potential application in AD treatment.
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