In this study, a series of new fluorine or chlorine-substituted cinnamic acid derivatives that contain tertiary amine side chain were designed, synthesized, and evaluated in acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition. The results show that almost all the derivatives containing tertiary amine side chain (compounds 4a-9d) exhibit moderate or potent activity in AChE inhibition. By contrast, their parent compounds (compounds 3a-3f) in the absence of tertiary amine moitery exhibit poor inhibitory activity against AChE. For the compounds containing pyrroline or piperidine side chain, the bioactivity in AChE inhibition is much intense than those containing N,N-diethylamino side chain. The chlorine or fluorine substituted position produces a significant effect on the bioactivity and selectivity in AChE inhibition. Most of the compounds that contain para-substituted fluorine or chlorine exhibit potent activity against AChE and poor activity against BChE, while ortho-substituted analogs show the opposite effect. It is worth noticing that the compounds containing N,N-diethylamino side chain are exceptions to this pattern. Among the newly synthesized compounds, compounds 6d are the most potent in AChE inhibition (IC50 = 1.11 ± 0.08 μmol/L) with high selectivity for AChE over BChE (selectivity ratio: 46.58). An enzyme kinetic study of compounds 6d suggests it produces a mixed-type inhibitory effect in AChE.
Keywords: cholinesterase inhibitors; cinnamic acid; halogen.
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