Bioassay-guided isolation and identification of anti-Alzheimer’s active compounds from Spiranthes sinensis (Pers.) Ames

A bioassay-guided approach was employed to identify the active compounds from the whole herb of Spiranthes sinensis (Pers.) Ames, an orchidaceous medicinal plant. As a result, fourteen compounds were obtained from the active fractions. The structures of the isolates were identified as methyl 4-[2-(butoxymethyl)-5-formyl-pyrrol-1-yl] butyrate (1), 5,3′-dihydroxy-3,7,4′-trimethoxyflavone (2), populnin (3), scutellarein (4), quercetin (5), kaempferol (6), stigmasterol-3-O-β-D-glucopyranoside (7), β-daucosterol (8), trans-p-hydroxy cinnamic acid (9), 4-hydroxybenzoic acid methyl ester (10), 3-(4-tolyloxy)-propanoic acid (11), 2-benzothiazolol (12), ethyl ferulate (13) and kumatakenin (14) by comparing the spectroscopic data from the isolated compounds with the data reported in the literature. Compound 1 was a new natural compound. Compounds 2, 4–6 and 9–14 were first reported from the genus Spiranthes. Compound 7 was isolated from S. sinensis for the first time. In addition, compounds 5, 6, 11 and 13 were found to have potent anti-acetylcholinesterase (anti-AChE) activities with IC50 values ranging from 8.63 ± 0.37 to 19.97 ± 1.05 μg/mL, which indicates that S. sinensis has the potential in the development of new anti-Alzheimer’s disease (anti-AD) drugs.