Isolation and structure elucidation of kadlongilactones C-F from Kadsura longipedunculata by NMR spectroscopy and DFT computational methods

Four new triterpenoids, kadlongilactones C-F (2-5), containing a consecutive hexacyclic [7,7,5,6,6,6] ring system, were isolated from the leaves and stems of Kadsura longipedunculata. In comparison with the NMR data of kadlongilactones A (1) and D (3), a significant phenomena was discovered that ring D of 3 inverted from a half-chair in 1 to a half-boat conformation when the HO-16 group changed from alpha- to beta-orientation. The structures of 2-5 were established on the basis of detailed spectroscopic analysis, and DFT computational methods were applied in the structural validation of compounds 3 and 5. Compounds 1-4 showed significant cytotoxicity against A549, HT-29, and K562 cell lines with IC50 values of 0.49-3.61 microM in vitro.