Cytotoxic Nitrogenous Terpenoids from Two South China Sea Nudibranchs , , and Their Sponge-Prey .

A detailed chemical investigation of two South China Sea nudibranchs and , as well as their possible sponge-prey , led to the isolation of one new nitrogenous cadinane-type sesquiterpenoid xidaoisocyanate A (), one new naturally occurring nitrogen-containing kalihinane-type diterpenoid bisformamidokalihinol A (), along with 17 known nitrogenous terpenoids (⁻, ⁻). The structures of all the isolates were elucidated by detailed spectroscopic analysis and by the comparison of their spectroscopic data with those reported in the literature. In addition, the absolute stereochemistry of the previously reported axiriabiline A () was determined by X-ray diffraction (XRD) analysis. In a bioassay, the bisabolane-type sesquiterpenoids , , and exhibited cytotoxicity against several human cancer cell lines.