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 IC(50) = 0.09 and 0.32 microg/ml, respectively.