Coriaceumins A-D, the First Nitrogen-Containing Crenulide Diterpenoids from the Brown Alga Dictyota coriacea Collected in the East China Sea.

A phytochemical investigation of an East China Sea collection of the brown alga Dictyota coriacea has led to the isolation of four novel nitrogen-containing crenulide diterpenoids, named coriaceumins A-D ( 1 - 4 ), two rare nitrogenous xenicane diterpenoids, dictyolactams C ( 5 ) and D ( 6 ), and one known crenulide diterpenoid, hydroxycrenulide ( 7 ). The structures of the new compounds were elucidated by detailed spectroscopic data analyses, including HRESIMS and 1D/2D NMR. The absolute configurations were determined by a comparison of the experimental ECD spectra with the spectra computed by DFT-based quantum chemical calculations. Coriaceumins A-D ( 1 - 4 ) represent the first examples of nitrogen-containing crenulide diterpenoids. In a bioassay, compounds 2 , 3 , 5 , and 7 were found to exhibit different levels of inhibitory effects against protein tyrosine phosphatase 1B (PTP1B) with IC 50 values ranging from 7.3 to 19 μM. In addition, the primary structure-activity relationships of all the isolates were summarized.