Cytotoxic ent-kaurene diterpenoids from Isodon phyllostachys

Five ent-kaurene diterpenoids, phyllostachysins D-H (1-5), together with nine known compounds, rabdoloxins A-B (6-7), rabdoinflexin B (8), amethystoidin A (9), rabdokunmin D (10), macrocalyxin E (11), a flavonoid, 5,7-dihydroxy-4′-hydroxylflavone (12), oleanolic acid (13) and daucosterol (14), were isolated from the aerial parts of Isodon phyllostachys. Structures were elucidated on the basis of spectroscopic methods, especially the 2D-NMR spectroscopic analysis. All ent-kaurenoids were tested for their cytotoxic effects against K562 cells. Compound 9 was the most potent with an IC50 value of 0.69 μg/ml.