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 2α-hydroxyoplopanone (1), oplopanone (2), 1β,4β,6α-trihydroxy-eudesmane (3), 1β,4β,7α-trihydroxy-eudesmane (4) and bullatantriol (5) were isolated from Homalomena pendula. The structure of the previously reported compound, 5,7-diepi-2α-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. [ABSTRACT FROM AUTHOR]