Two cytotoxic 6,7-seco-spiro-lacton-ent-kauranoids from Isodon rubescens.

The present study was performed to investigate the chemical components of the branches and leaves of Isodon rubescens. Two 6,7-seco-spiro-lacton-ent-kauranoids were obtained. Based on the extensive spectroscopic analyses, their structures were elucidated as 6-epi-11-O-acetylangustifolin (1) and 11-O-acetylangustifolin (2), respectively. The structure of 2 was further comfirmed by X-ray crystallography analysis. MTT method was employed to evaluate their cytotoxity against human lung cancer cell lines A549 and leukemia cell lines K562.