Structure revision and absolute configuration of 5,7- diepi-2α -hydroxyoplopanone and anti-osteoporotic activities of sesquiterpenoids from the rhizomes of Homalomena pendula .

Five sesquiterpenoids including 2 α -hydroxyoplopanone (1) , oplopanone ( 2 ), 1 β ,4 β ,6 α -trihydroxy-eudesmane ( 3 ), 1 β ,4 β ,7 α -trihydroxy-eudesmane ( 4 ) and bullatantriol ( 5 ) were isolated from Homalomena pendula . The structure of the previously reported compound, 5,7- diepi -2 α -hydroxyoplopanone ( 1a ), has been revised to 1 by the spectroscopic evidences (1D-/2D-NMR, IR, UV and HRESIMS) and by comparison between experimental and theoretical NMR data using DP4+ protocol. Furthermore, the absolute configuration of 1 was unambiguously assigned by ECD experiments. Compounds 2 and 4 displayed a potent ability to stimulate osteogenic differentiation of MC3T3-E1 cells at 4 µg/mL (by 123.74% and 131.07%, respectively) and 20 µg/mL (by 112.45% and 126.41%, respectively) whilst 3 and 5 did not show any activities. At 20 µg/mL, 4 and 5 significantly promoted the mineralization of MC3T3-E1 cells with values of 112.95% and 116.37%, respectively, whereas 2 and 3 were inactive. The results indicated that 4 could be an excellent component for anti-osteoporosis studies from the rhizomes of H. pendula .