Boswellianols A-I, Structurally Diverse Diterpenoids from the Oleo-Gum Resin of and Their TGF- Inhibition Activity.

Olibanum, a golden oleo-gum resin from species in the genus ( family), is a famous traditional herbal medicine widely used around the world. Previous phytochemical studies mainly focused on the non-polar fractions of olibanum. In this study, nine novel diterpenoids, boswellianols A-I (-), and three known compounds were isolated from the polar methanolic fraction of the oleo-gum resin of . Their structures were determined through comprehensive spectroscopic analysis as well as experimental and calculated electronic circular dichroism (ECD) data comparison. Compound is a novel diterpenoid possessing an undescribed prenylmaaliane-type skeleton with a 6/6/3 tricyclic system. Compounds - were unusual prenylaromadendrane-type diterpenoids, and compounds - were new highly oxidized cembrane-type diterpenoids. Compounds and showed significant transforming growth factor (TGF-) inhibitory activity via inhibiting the TGF--induced phosphorylation of Smad3 and the expression of fibronectin and N-cadherin (the biomarker of the epithelial-mesenchymal transition) in a dose-dependent manner in LX-2 human hepatic stellate cells, indicating that compounds and should be potential anti-fibrosis agents. These findings give a new insight into the chemical constituents of the polar fraction of olibanum and their inhibitory activities on the TGF-/Smad signaling pathway.