Ent-kaurane diterpenoids from Rabdosia rubescens and their cytotoxic effects on human cancer cell lines.

Two new ent-kaurane diterpenoids, 16,17-exo-epoxide-oridonin ( 1) and 11,15- O,O-diacetyl-rabdoternins D ( 2), together with thirteen known ones, were isolated from the aerial parts of Rabdosia rubescens. Their structures were established on the basis of high-field 1D and 2D NMR methods supported by HRMS. All diterpenoids were tested for cytotoxicity against human Hep G2, COLO 205, MCF-7, and HL-60 cancer cells. The compounds oridonin ( 3), 14- O-acetyl-oridonin ( 4), 1,14- O,O-diacetyl-oridonin ( 5), rosthorin ( 6), effusanin E ( 7), and ponicidin ( 8), as well as six alpha-methylene gamma-ketone bearing diterpenoids, were modestly active in these assays.