Alkaloids from the bulbs of Lycoris longituba and their neuroprotective and acetylcholinesterase inhibitory activities.

Three novel alkaloids (1-3), together with nineteen known ones (4-22), were isolated from the bulbs of Lycoris longituba. Their structures were elucidated on the basis of extensive spectroscopic analyses, which belong to several Amaryllidaceae alkaloid skeletons. Among them, the harmane-type alkaloids (the new compound 1 and the known compounds 5, 6 and 7) were found for the first time from Lycoris genus. The isolates were tested for their neuroprotective activities against CoCl2, H2O2 and Aβ25-35-induced SH-SY5Y cell injuries, and the majority of them exhibited neuroprotective activities of different degrees. The acetylcholinesterase (AChE) inhibitory activities of the isolated alkaloids were also evaluated, while compounds 12, 14-20 and 22 exhibited extremely significant AChE inhibitory activities.