Synthesis and Biological Evaluation of Coumarin Triazoles as Dual Inhibitors of Cholinesterases and β-Secretase

Abstract

Coumarin is a naturally occurring bioactive pharmacophore with wide occurrence among central nervous system (CNS)-active small molecules. 8-Acetylcoumarin, one of the natural coumarins, is a mild inhibitor of cholinesterases and β-secretase, which are vital targets of Alzheimer's disease. Herein, we synthesized a series of coumarin-triazole hybrids as potential multitargeted drug ligands (MTDLs) with better activity profiles. The coumarin-triazole hybrids occupy the cholinesterase active site gorge from the peripheral to the catalytic anionic site. The most active analogue, 10b, belonging to the 8-acetylcoumarin core, inhibits acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-secretase-1 (BACE-1) with IC₅₀ values of 2.57, 3.26, and 10.65 μM, respectively. The hybrid, 10b, crosses the blood-brain barrier via passive diffusion and inhibits the self-aggregation of amyloid-β monomers. The molecular dynamic simulation study reveals the strong interaction of 10b with three enzymes and forming stable complexes. Overall, the results warrant a detailed preclinical investigation of the coumarin-triazole hybrids.

Figure 1

Chemical structures of coumarin derivatives 1–3 and triazole 4 that are reported to show dual ChE/BACE-1 inhibition. The proposed coumarin–triazole series is also shown with general structure A. Here, the coumarin may be connected to the triazole through ring A or B.

Scheme 1. Synthesis of Coumarin A-Ring Connected Triazole Hybrids, 8a–p

Reagents and conditions: (a) propargyl bromide, K₂CO₃, dimethylformamide (DMF), 70 °C, 24 h, reflux, 95%; (b) TEA, sodium ascorbate, CuSO₄·5H₂O, room temperature (rt), 24 h, 54–85%.

Scheme 2. Synthesis of Coumarin B-Ring Connected Triazole Hybrids, 10a–d, 13a–d, 16a–d, and 19a–d

Reagents and conditions: (a) propargyl bromide, K₂CO₃, DMF, 70 °C, 24 h, reflux, 75–91%; (b) TEA, NaN₃, sodium ascorbate, CuSO₄·5H₂O, rt, 24 h, 50–80%; (c) methyl iodide, NaH, DMF, 0 °C, 90%.

Figure 2

Enzyme kinetics and molecular modeling studies of 10b with AChE, BChE, and BACE-1. (A) LB plot for inhibition of AChE by 10b; (B) molecular docking of 10b with AChE (PDB: 4EY7); (C) LB plot for inhibition of BChE by 10b; (D) molecular docking of 10b with BChE (PDB: 6EP4); (E) LB plot for inhibition of BACE-1 by 10b; (F) molecular docking of 10b with the BACE-1 (PDB: 1W51). The light blue dotted lines indicate π–π interactions, and the dark red dotted lines indicate H-bonding interactions.

Figure 3

Interaction pattern of 3,5-dimethoxybenzyl coumarin–triazole hybrids, 10b, 8o, and 19b with AChE (PDB: 4EY7).

Figure 4

MD simulation of 10b–AChE complex for 50 ns. (A) Protein–ligand RMSD during simulation; (B) RMSF of AChE; (C) RMSF of compound 10b; (D) interaction pattern of compound 10b with AChE during MD simulation; (E) two-dimensional (2D) diagram for the interaction of compound 10b with AChE.

Figure 5

MD simulation of 10b–BChE complex for 50 ns. (A) Protein–ligand RMSD during simulation; (B) RMSF of BChE; (C) RMSF of compound 10b; (D) interaction pattern of compound 10b with BChE during MD simulation; (E) 2D diagram for compound 10b interactions with BChE.

Figure 6

MD simulation of 10b–BACE-1 complex for 50 ns. (A) Protein–ligand RMSD during simulation; (B) RMSF of BACE-1; (C) RMSF of compound 10b; (D) interaction pattern of compound 10b with BACE-1 during MD simulation; (E) 2D diagram for compound 10b interactions with BACE-1.

Figure 7

Molecular docking of curcumin (A) and compound 10b (B) with the Aβ monomer (PDB: 1Z0Q).