Heliosterpenoids A and B, two Novel Jatrophane-Derived Diterpenoids with a 5/6/4/6 Ring System from Euphorbia helioscopia.

Heliosterpenoids A and B (1 and 2), two unprecedented jatrophane-derived diterpenoid esters with a novel 5/6/4/6-fused tetracyclic ring skeleton, were isolated from the whole plants of Euphorbia helioscopia. The structures of 1 and 2 were elucidated by extensive spectroscopic methods and electronic circular dichroism (ECD) analyses. The plausible biogenetic pathways of 1 and 2 were postulated. 1 and 2 were found to be potent inhibitors of P-glycoprotein (ABCB1) and 1 also exhibited cytotoxicity against MDA-MB-231 cell lines.