A New ent-Atisane Diterpenoid from the Stems of Euphorbia royleana

A new ent-atisane diterpenoid, named euphrosanoid A (1), along with five known analogues (2-6) were isolated from the stems of Euphorbia royleana. The structure of new compound 1 was determined by extensive spectroscopic data, especially 1D and 2D NMR experiments, and the absolute configuration of 1 was determined by comparison of experimental and calculated electronic circular dichroism (ECD) data. All isolated compounds were evaluated for their cytotoxic activities, and compounds 1 and 5 showed weak cytotoxicities against HCT-15 cancer cells with IC50 values of 62.98 +/- 6.27 and 44.35 +/- 3.66 mu M, respectively.