Diverse diterpenoids and sesquiterpenoids from Siegesbeckia pubescens and their activity against RANKL-induced osteoclastogenesis

Abstract

Phytochemical investigation of the aerial parts of Siegesbeckia pubescens led to seventeen diterpenoids (1–17) and twelve sesquiterpenoids (18–29). Their structures were varied including twelve ent-pimarane (1–12), three ent-kaurane (13–15), two acyclic diterpenoids (16–17), ten germacrene (18–27), one guaiane (28), and one caryolane (29) sesquiterpenoids. Eight of twenty-nine were new ones (1, 3, 4, 16–18, 23, and 28). Their structures were elucidated by extensive spectroscopic analysis. The absolute configurations of compounds 1 and 2 were identified using X-ray diffraction analysis, and of compounds 18, 23, and 28 were elucidated by the experimental and calculated electronic circular dichroism (ECD) spectra. All the isolated compounds (1–29) were assayed for their inhibition of RANKL-induced osteoclastogenesis in bone marrow macrophages (BMMs). Four sesquiterpenoids 18, 25, 26, and 27 exhibited potent inhibition of osteoclastogenesis with IC50 value of 0.51, 0.80, 0.50, and 0.83 μM, respectively. Here we demonstrated that S. pubescens may be a resource for discovery of anti-osteoporosis agents.