Vietnamese Huperzia squarrosa was isolated from a sequence of lycopodium alkaloids, namely lycosquarosine A (1), acetylaposerratinine (2), huperzine A (3), huperzine B (4), 8pha-hydrophlemariurine B (5) and huperzinine (6). Among them, the latest natural source metabolite is lycosquarosine A (1). Dose-dependent AChE activity was completely inhibited by lycosquarosine A...