Discovery and Identification of Bioactive Organic Compounds From <i>Callistemon citrinus</i> (Bottlebrush) as Natural Inhibitors of Acetylcholinesterase (AChE) Enzyme via the Cholinergic Pathway for the Management of Alzheimer's Disease

ABSTRACT Alzheimer's disease (AD) is one of the most prevalent forms of dementia worldwide. Current AD treatment primarily aims to inhibit acetylcholinesterase (AChE), a key therapeutic target. In this study, 132 phytochemicals were collected from GC–MS, NMR, and GLC–MS and screened through ADMET (absorption, distribution, metabolism, excretion, and toxicity) analysis using 26 pharmacokinetic and toxicity parameters. Sixteen compounds passed the criteria and were selected for molecular docking, showing binding affinities of up to −8.5 kcal/mol and interacting at both the CAS (catalytic anioninc site) and PAS (peripheral anionic site) sites of AChE. The top six phytochemicals underwent molecular dynamics simulations. Results, including root mean square deviation (RMSD) (0.147–0.674 nm), root mean square fluctuation (RMSF) (0.072–0.112 nm), hydrogen bonds (0–4), radius of gyration (2.310–2.323 nm), and solvent‐accessible surface area (SASA) (212.745–221.204 nm 2 ), confirmed structural stability. Durohydroquinone and phthalic acid demonstrated the most stable binding. MM/PBSA (molecular mechanics poisson boltzmann surface area) and MM/GBSA (molecular mechanics generalized born surface area) binding energy calculations ranged from −13.56 to −5.90 kcal/mol and −15.71 to −14.87 kcal/mol, respectively, supporting strong ligand–receptor interactions. Frontier molecular orbital (FMO) analysis showed highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of 4–5 eV, indicating satisfactory kinetic stability and moderate reactivity. The lead compounds were compared with donepezil and showed better ADMET properties and comparable performance in molecular studies. Overall, the findings suggest that phytochemicals from Callistemon citrinus , particularly durohydroquinone and phthalic acid, hold potential as natural AChE inhibitors for managing AD.