Synthesis and structure-activity relationship of nuciferine derivatives as potential acetylcholinesterase inhibitors

Acetylcholinesterase inhibitors (AChEIs) are currently the best available pharmacotherapy for Alzheimer patients, but because of bioavailability issues, there is still great interest in discovering better AChEIs. The aporphine alkaloid is an important class of natural products, which shows diverse biological activity, such as acetylcholinesterase inhibitory activity. To find new lead AChEIs compounds, eight aporphine alkaloids were synthesized by O-dealkylation, N-dealkylation, and ring aromatization reactions using nuciferine as raw material. The anti-acetylcholinesterase activity of synthesized compounds was measured using modified Ellman's method. The results showed that some synthesized compounds exhibited higher affinity to AChE than the parent compound nuciferine. Among these compounds, 1,2-dihydroxyaporphine (2) and dehydronuciferine (5) were the most active compounds (IC50 = 28 and 25 mu g/mL, respectively). Preliminary analysis of structure-activity relationships suggested that aromatization of the C ring, the presence of the alkoxyl group at C1 and the hydroxy group at C2 position as well as the alkyl substituent at the N atom were favorable to the acetylcholinesterase inhibition. Molecular docking was also applied to predict the binding modes of compounds 1, 2, and 9 into the huperzine A binding site of AChE.