Heliojatrones A and B, Two Jatrophane-Derived Diterpenoids with a 5/10 Fused -Ring Skeleton from Euphorbia helioscopia: Structural Elucidation and Biomimetic Conversion

Heliojatrones A and B (1 and 2), two jatrophane-derived diterpenoids with an unprecedented trans-bicyclo[8.3.0]tridecane core, were isolated from the whole plants of Euphorbia helioscopia. Their structures and absolute configurations were unequivocally determined by a combination of spectroscopic data, electronic circular dichroism calculations, biomimetic conversion, and X-ray diffraction analyses. Their plausible biosynthetic pathways were also proposed. Compounds 1 and 2 were biomimetically synthesized from 3 and 4 through a photochemical rearrangement reaction of beta, gamma -unsaturated ketone, respectively. Compound 2 showed significant P-glycoprotein inhibitory activity compared with the positive control (cydosporine A).