Nototronesides A–C, Three Triterpene Saponins with a 6/6/9 Fused Tricyclic Tetranordammarane Carbon Skeleton from the Leaves of Panax notoginseng

Three triterpene saponins, nototronesides A–C (1–3), possessing an unprecedented 6/6/9 fused tricyclic tetranordammarane core, were isolated from the leaves of Panax notoginseng. Their structures were elucidated on the basis of spectroscopic data, and the structure of sapogenin (1a) was further confirmed by X-ray crystallography. The existence of 1–3 adds a new dimension to the diversity of the triterpene family. Moreover, compound 2 showed a moderate neuroprotective effect on serum deficiency-induced cellular damage in PC12 cells.