Bioactive ent-kaurane diterpenoids from Isodon rubescens.

Seven previously undescribed 7,20-epoxy-ent-kaurane diterpenoids, isojiangrubesins A-G, along with seventeen known ones, were isolated from the aerial parts of Isodon rubescens. Their structures were characterized on the basis of spectroscopic methods and signal-crystal X-ray diffraction. All of these compounds were evaluated for their in vitro cytotoxicity against five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW480). Four isolates exhibited significant inhibitory ability against all cell lines, with IC50 values ranging from 0.5 to 6.5 µM; They also strongly inhibited NO production in LPS-stimulated RAW264.7 cells.