Neolignans and amide alkaloids from the stems of Piper kadsura and their neuroprotective activity.

Four undescribed neolignans and three undescribed amide alkaloids, along with twelve known compounds, were isolated from the stems of Piper kadsura (Choisy) Ohwi. The structures of the new compounds were determined by spectroscopic analysis, quantum-chemical calculations, and Mo(OAc)-induced ECD analysis. The neuroprotective effects of these compounds against Aβ-induced cell damage in PC12 cells were investigated, and eight compounds exhibited significant neuroprotective effects against Aβ-induced PC12 cell damage, with the EC values of 3.06-29.3 μM. Three of these compounds were selected for further experiments, and they appear to reduce apoptosis and enhance autophagy against Aβ-induced PC12 cell damage.