Potential Anti-Cholinesterase Activity of Bioactive Compounds Extracted from Cassia grandis L.f. and Cassia timoriensis DC

Acetylcholinesterase (AChE) inhibitors remain the primary therapeutic drug that can alleviate Alzheimer's disease's (AD) symptoms. Several Cassia species have been shown to exert significant anti-AChE activity, which can be an alternative remedy for AD. Cassia timoriensis and Cassia grandis are potential plants with anti-AChE activity, but their phytochemical investigation is yet to be further conducted. The aims of this study were to identify the phytoconstituents of C. timoriensis and C. grandis and evaluate their inhibitory activity against AChE and butyrylcholinesterase (BChE). Two compounds were isolated for the first time from C. timoriensis: arachidyl arachidate (1) and luteolin (2). Five compounds were identified from C. grandis: β-sitosterol (3), stigmasterol (4), cinnamic acid (5), 4-hydroxycinnamic acid (6), and hydroxymethylfurfural (7). Compound 2 showed significant inhibition towards AChE (IC₅₀: 20.47 ± 1.10 µM) and BChE (IC₅₀: 46.15 ± 2.20 µM), followed by 5 (IC_50: 40.5 ± 1.28 and 373.1 ± 16.4 µM) and 6 (IC₅₀: 43.4 ± 0.61 and 409.17 ± 14.80 µM) against AChE and BChE, respectively. The other compounds exhibited poor to slightly moderate AChE inhibitory activity. Molecular docking revealed that 2 showed good binding affinity towards TcAChE (PDB ID: 1W6R) and HsBChE (PDB ID: 4BDS). It formed a hydrogen bond with TYR121 at the peripheral anionic site (PAS, 2.04 Å), along with hydrophobic interactions with the anionic site and PAS (TRP84 and TYR121, respectively). Additionally, 2 formed three H-bonds with the binding site residues: one bond with catalytic triad, HIS438 at distance 2.05 Å, and the other two H-bonds with GLY115 and GLU197 at distances of 2.74 Å and 2.19 Å, respectively. The evidence of molecular interactions of 2 may justify the relevance of C. timoriensis as a cholinesterase inhibitor, having more promising activity than C. grandis.