Discovery of diverse diterpenoid scaffolds from Euphorbia antiquorum and their activity against RANKL-induced osteoclastogenesis.

Seven new diterpenoids, euphorantones A-D (1, 3, 6, and 10), 8,12,13-epi-3,7,12-O-triacetyl-8-O-(2-methylbutanoyl)-ingol (9), 8,12,13-epi-3,12-O-diacetyl-7-O-benzoyl-8-methoxyingol (11), 2,3-epi-7,12-diacetate-8-benzoate-ingol (12), together with eighteen known compounds (2, 4-5, 7-8, and 13-25), were isolated from the aerial parts of Euphorbia antiquorum L.. The structures of new compounds 1, 3, 6, and 9-12 were elucidated by extensive spectroscopic analyses. The absolute configurations of new compounds were assigned using X-ray diffraction, Rh2(OCOCF3)4-induced CD spectrum, and confirmed through comparison of the calculated and experimental 13C NMR and electronic circular dichroism (ECD) data. Compounds 1-25 were evaluated for their inhibition of RANKL-induced osteoclastogenesis. Compound 1 showed the most potent inhibition of RANKL-induced osteoclastogenesis with IC50 value of 0.3 μM. It inhibited NFAT transcript activity and osteoclast related genes TRAcP, CTSK, and NFATc1 expression.