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 IC50 values ranging from 0.3 to 7.3 mug/mL. The structure of 6 was revised on the basis of its 2D-NMR spectral data.