Sinuhirtone A, An Uncommon 17,19-Dinorxeniaphyllanoid, and Nine Related New Terpenoids from the Hainan Soft Coral Sinularia hirta .

Chemical investigation of the Hainan soft coral Sinularia hirta resulted in the isolation and identification of a library of sixteen structurally diverse terpenoids, including a dinorditerpenoid with an uncommon 17,19-dinorxeniaphyllane skeleton, namely sinuhirtone A ( 7 ), six new xeniaphyllane-type diterpenoids ( 1 - 6 ), one new norxeniaphyllanoid ( 8 ), two new norcaryophyllene-type sesquiterpenoids ( 9 and 10 ), together with six known related compounds ( 11 - 16 ). Compounds 1 - 3 are three new furanone-containing xeniaphyllane-type diterpenoids. The structures of the new compounds, including their absolute configurations, were determined by extensive spectroscopic analysis and a series of quantum chemical calculations, including quantum mechanical-nuclear magnetic resonance (QM-NMR), time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD), and optical rotatory dispersion (ORD) methods. A plausible biosynthetic connection between new compounds 1 - 9 was also proposed. New compounds 2 - 4 , 7 , and 8 were evaluated for in vitro cytotoxicity against four cancer cell lines.