Acetylcholinesterase inhibitory active constituents of the endophytic fungus <italic>Alternaria alternata</italic> FL7 isolated from <italic>Huperzia serrata</italic>

This study primarily investigates the acetylcholinesterase (AChE) inhibitory components in the fermentation product of the endophytic fungus Alternaria alternata FL7 from Huperzia serrata. Using silica gel column chromatography, preparative high-performance liquid chromatography (preparative HPLC), nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectrometry (HR-ESI-MS), 19 monomeric compounds were isolated and identified. These include mannitol (1), uracil (2), alternariol monomethyl ether (3), cerevisterol (4), 1-methyl 5-acetamidopentanoate (5), cyclo (L-Pro-L-Pro) (6), stigmasterol (7), xanthine (8), 2(3H)-benzothiazolethione (9), catechol (10), 1-methyl β-D-glucopyranoside (11), cycol (L-Pro-L-Tyr) (12), cycol (L-Pro-L-Val) (13), alteamide (14), (4S,5S)-5-[(S)-sec-butyl]-4-hydroxypyrrolidin-2-one (15), allahabadolactones A (16), Bis(2-ethylhexyl) phthalate (17), methyl 4-acetamidobutanoate (18) and 2-phenylethyl α-D-glucopyranoside (19). Compound 3 was found to exhibit moderate AChE inhibitory activity with an IC50 value of (15.8±0.13) µmol/L, as determined using the modified Ellman method. Molecular docking simulations suggest that serine at position 122 of AChE may be its binding target. Additionally, compounds 5, 15, and 18 are reported as newly identified natural products, and the structure of compound 14 is revised. This study provides reference for the development and utilization of microbial resources from Huperzia serrata.