LC-MS guided isolation of cytotoxic saponins from the flower buds of Lonicera macranthoides

Two undescribed triterpenoid saponins (1 and 3) along with six known saponins (2, 4-8) were isolated from the flower buds of Lonicera macranthoides by an LC-MS guided fractionation method. Natural products 1, 3, 5 and 7 are the monodesmosidic saponins of ambradiolic acid, 23-hydroxybetulinic acid, hederagenin and oleanolic acid, respectively, sharing the same single sugar chain at C-3 of each aglycone. Furthermore, compounds 2, 4, 6 and 8 are their bisdesmosidic saponins with a further identical sugar chain at C-28 of the aglycone. All structures were identified by interpretation of their spectroscopic data. Compounds 1-8 were evaluated for in vitro cytotoxicity against the HeLa, HTC-116, B16 and MDA-MB-468 cell lines. Results showed that all monodesmosidic saponins exhibited moderate activity with compound 7 showing the most pronounced cytotoxicity against the four human cancer cell lines, with IC50 values of 1.9–13.5 μM. The preliminary structure-activity relationships of the natural products are also discussed.