Structural Characterization and Antioxidative Activity of Lancifonins: Unique Nortriterpenoids from Schisandra lancifolia

ABSTRACT: Six unique nortriterpenoids, lancifonins A−F (1−6), were isolated from Schisandra lancifolia. Their absolute configurations were determined by X-ray diffraction and ECD calculation. The conformational analysis of 1 was performed due to the unanticipated changes of Cotton effects in its ECD spectrum. Compounds 5 and 6 possess a unique 7/7 fused carbocyclic core with an internal ester bridge between C-9 and C-14, and 5 exhibited protective activity against H2O2-induced oxidative damage on Caco-2 cells. Plants of the Schisandra genus are rich sources of highlyoxygenated and rearranged norcycloartane-type triterpe-noids named schinortriterpenoids (SNTs).1 The discovery of the first member of SNT micrandilactone A2 in 2003 is a prelude to numerous research on this class of molecules in the fields of phytochemistry1 and organic synthesis.1,3 Schisandra lancifolia (Rehd. et Wils.) A. C. Smith, especially distributed in the Nujiang prefecture of Yunnan province in China, could be considered to be a prominent producer of novel SNTs,4 which make this species eminently rewarding to systematic research. As a result of continuing investigation on architecturally interesting SNTs with bioactivities from this species, six unique and biogenetically related SNTs, lancifonins A−F (1−6), were discovered. Their absolute configurations were established by X-ray diffraction and ECD calculation. The ECD spectrum of 1 was serendipitously found to be a special case in SNTs, when compared to those of other (20R)-16,17-seco-preschisanartane-type SNTs. Therefore, its conformational analysis was performed. Most notably, 5 and 6 possess an unprecedented rearranged carbocyclic core with an internal ester bridg