An ellagitannin monomer, lythracin M (1), and a dimer, lythracin D (2), along with eight known monomers (3-10) were isolated from Lawsonia inermis (Lythraceae) leaves. Lythracin M (1) is a C-glycosidic ellagitannin with a flavogallonyl dilactone moiety that participates in the creation of a γ-lactone ring with the anomeric carbon of the glucose core. Lythracin D (2) was determined as an atropisomer of the reported lythcarin D. These newly discovered structures (1 and 2) were determined by intensive spectroscopic experiments and by comparing DFT-calculated 1H1H coupling, 1H NMR chemical shifts, and ECD data with experimental values. The anti-acetylcholinesterase assay of the compounds 1-10 revealed that the C-1 ellagitannin epimers [casuarinin (7; IC50 = 34 ± 2 nM) and stachyurin (8; IC50 = 56 ± 3 nM)], and the new dimer (2; IC50 = 61 ± 4 nM) possess enzyme inhibitory effects comparable to the reference drug (donepezil, IC50 = 44 ± 3 nM). Molecular docking of compounds 1-10 with AChE identified the free galloyl moiety as an important pharmacophore in the anticholinesterase activity of tannins.
Keywords: Anticholinesterase; DFT calculations; Ellagitannins; Lawsonia inermis; Lythraceae; Molecular docking.
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