Three new ent-kaurane diterpenoids from Isodon rubescens and their cytotoxicities

AIM: To study the chemical constitutions of the aerial parts of Isodon rubescens in Jianshi county, Hubei Province, China. METHOD: Compounds 1-9 were isolated and purified by normal silica gel and C18 reversed phase silica gel column chromatography, and HPLC. Their structures were elucidated by extensive spectroscopic methods (IR, UV, MS and NMR), and the absolute configuration of 1 was determined by single crystal X-ray diffraction. Compounds 1-9 were evaluated for their in vitro cytotoxicity against human tumor HL-60, SMMC-7721, A-549, MCF-7, and SW-480 cell lines. RESULT: Eight ent-kaurane diterpenoids and one ent-gibberellanoid were isolated and identified. CONCLUSIONS: Compounds 1-3 (jianshirubesins G-I) were new diterpenoids, of which 2 was a rare 3, 20-epoxy-ent-kaurane with a hemiketal at C-3. Among all of the diterpenoids tested, compounds 4 and 5 exhibited moderate inhibitory activity on the proliferation of certain cancer cells.