Lycopodium Alkaloids from Vietnamese Huperzia squarrosa (Forst.) Trevis and Their Anti-cholinesterase Activity

A series of Lycopodium alkaloids, namely lycosquarosine A (1), acetylaposerratinine (2), huperzine A (3), huperzine B (4), 8?-hydrophlemariurine B (5) and huperzinine (6), has been isolated from Vietnamese Huperzia squarrosa. Among them, lycosquarosine A (1) is the new metabolite of the natural source. Lycosquarosine A completely inhibited AChE activity in a dose dependent manner with an IC50 value of 54.3 ?g/mL, while acetylaposerratinine (2) showed stronger inhibitory activity than 1 with an IC50 value of 15.2 µg/mL. This result indicates that these alkaloids may be a potent source of AChE inhibitors. This is the first report on the alkaloid constituents of H. squarrosa from Vietnam and the potential cholinesterase inhibitory activity of these compounds might suggest new sources of anti-Alzheimer disease agents.