Novel 2-pheynlbenzofuran derivatives as selective butyrylcholinesterase inhibitors for Alzheimer's disease

Abstract

Alzheimer's disease (AD) is a neurodegenerative disorder representing the leading cause of dementia and is affecting nearly 44 million people worldwide. AD is characterized by a progressive decline in acetylcholine levels in the cholinergic systems, which results in severe memory loss and cognitive impairments. Expression levels and activity of butyrylcholinesterase (BChE) enzyme has been noted to increase significantly in the late stages of AD, thus making it a viable drug target. A series of hydroxylated 2-phenylbenzofurans compounds were designed, synthesized and their inhibitory activities toward acetylcholinesterase (AChE) and BChE enzymes were evaluated. Two compounds (15 and 17) displayed higher inhibitory activity towards BChE with IC₅₀ values of 6.23 μM and 3.57 μM, and a good antioxidant activity with EC₅₀ values 14.9 μM and 16.7 μM, respectively. The same compounds further exhibited selective inhibitory activity against BChE over AChE. Computational studies were used to compare protein-binding pockets and evaluate the interaction fingerprints of the compound. Molecular simulations showed a conserved protein residue interaction network between the compounds, resulting in similar interaction energy values. Thus, combination of biochemical and computational approaches could represent rational guidelines for further structural modification of these hydroxy-benzofuran derivatives as future drugs for treatment of AD.

Figure 1

Protocol for synthesis of compounds. (a) scheme 1 (b) scheme 2.

Figure 2

Kinetic study on the mechanism of eqBChE inhibition by compound 15. (a) Lineweaver-Burk plots for inhibition of compound 15 on eqBChE activity. The concentrations of inhibitor were 0 (○), 2 (●), 4 (□), 6 (■) and 8 (∆) µM. (b) The secondary plot of slope (K_m/V_max) versus compound concentration. (c) The secondary plot of 1/V_max versus compound concentration.

Figure 3

Kinetic study on the mechanism of eqBChE inhibition by compound 17. (a) Lineweaver–Burk reciprocal plots of eqBChE initial velocity at increasing substrate concentrations (0.05–0.5 mM). The concentrations of inhibitor were 0 (○), 1 (●), 2 (□), 5 (■) and 10 (∆) µM. (b) The secondary plot of slope (K_m/V_max) versus compound concentration. (c) The secondary plot of 1/V_max versus compound concentration.

Figure 4

Effect of compound 15 and 17 on NSC-34 cell viability.

Figure 5

Molecular Modeling. (a) Superimposition of best-docked positions of compounds 17 (blue) and 15 (red) into binding site of hBChE protein. The protein is represented in cartoon representation, the active site residues in licorice, and loops leading to hBChE active site are shown. (b) Zoomed representation of hBChE interaction site for the two compounds, and key residues are shown. (c) RMSD plots for the free and compound-bound hBChE simulations. (d) Interaction energy plots between the compound and hBChE residues.

Figure 6

Molecular interaction picture of hBChE protein bound to (a) compound 17 and (b) compound 15. The conserved interactions between the two complexes are represented as red circles.

Figure 7

Dynamical cross-correlation map for C-alpha atoms. (a) Free hBChE, (b) compound 17 and (c) compound 15 complexes. Positive correlations are indicated in red and negative or anti-correlations in blue, while no correlation in white. In (b) and (c) boxed regions represent those regions different with respect to free hBChE protein. While in (b), the dashed box for compound 17 represents the region different with respect to both the free and compound 15 complexes.