New Cembranoid Diterpenes from the Vietnamese Soft Coral Sarcophyton mililatensis Stimulate Osteoblastic Differentiation in MC3T3-E1 Cells

Chemical investigation of the Vietnamese soft coral Sarcophyton mililatensis resulted in the isolation of four new cembranoid diterpenes, namely (−)-7β-hydroxy-8α-methoxydeepoxysarcophytoxide (1), (+)-7β,8β-dihydroxydeepoxysarcophytoxide (2), (−)-17-hydroxysarcophytonin A (3) and sarcophytol V (4), along with two known compounds, (+)-sarcophine (5) and sarcophytoxide (6). The NMR spectral data of the new compounds were completely assigned by using a combination of 2D NMR experiments including 1H–1H COSY, HSQC, HMBC, and ROESY. To investigate the bioactivities of compounds, which act on bone metabolism, we studied the effects of compounds on the function of osteoblastic MC3T3-E1 cells. Compound 1 caused a significant elevation of alkaline phosphatase activity, collagen content, and nodules mineralization compared to those of the control (p