Cytotoxic ent-kaurane diterpenoids from Isodon macrophyllus.

Two new ent-kaurane diterpenoids, dayecrystals D-E (1-2), together with nine known compounds, isojaponin A (3), rabdosin A (4), lushanrubescensin J (5), wikstroemioidin B (6), maoyecrystal C (7), rabdosin B (8), isodonal (9), shikokianin (10), and effusanin A (11), were isolated from the leaves of Isodon macrophyllus. The structures of the new compounds were elucidated using 1D and 2D NMR spectroscopy. The (13)C-NMR spectral data of compound 4 are reported for the first time. All of the compounds were tested for their cytotoxicities against DU145 and LoVo human tumor cells. Compounds 4, 10, and 11 showed inhibitory effects on DU145 cells with IC(50) values 5.90, 4.24, and 3.16 microM, and LoVo cells with IC(50) values 14.20, 17.55, and 3.02 microM, respectively.