Cytotoxic ent-kaurane diterpenoids from Isodon rubescens var. rubescens.

Five new ent-kauranoids, xindongnins C - G ( 1 - 5), together with five known ones, xindongnins A and B ( 6 and 7), melissoidesin G ( 8), dawoensin A ( 9), and glabcensin V ( 10), were isolated from the leaves of Isodon rubescens var. rubescens, and structurally elucidated. Compounds 1, 4, and 6 - 10 showed inhibitory effects against human tumor K562 cells with IC (50) values ranging from 0.3 to 7.3 microg/mL. The structure of 6 was revised on the basis of its 2D-NMR spectral data.