Structure and Cytotoxicity of Diterpenoids from Isodon adenolomus

Twelve new diterpenoids, isoadenolins A-L (1-12), and 24 known ones were isolated from the aerial parts of Isodon adenolomus. Their structures were identified using spectroscopic data, and the absolute configurations of 1 and 14 were determined by single-crystal X-ray diffraction. Selected compounds were evaluated for their in vitro cytotoxicity against human tumor HL-60, SMMC-7721, A-549, MCF-7, and SW-480 cell lines. Compounds 9, 13-16, and 21 showed significant inhibitory effects on all five cells, with IC50 values in the range 0.7-9.7 μM.