ent-kaurane diterpenoids from the leaves of Isodon xerophilus

From the ethanolic extract of the leaves of Isodon xerophilus, three new ent-kaurane diterpenoids named xerophilusins L-N (1-3), together with three known ones designated as rabdoternin A (4), longikaurin F (5) and ponicidin (6), were isolated and structurally elucidated. Compound 6 demonstrated most potent cytotoxic activity against K562 and T24 human tumor cell lines with IC50 = 0.09 and 0.32 mug/ml, respectively.