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

A phytochemical investigation of an East China Sea collection of the brown alga has led to the isolation of four novel nitrogen-containing crenulide diterpenoids, named coriaceumins A-D (-), two rare nitrogenous xenicane diterpenoids, dictyolactams C () and D (), and one known crenulide diterpenoid, hydroxycrenulide (). 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 (-) represent the first examples of nitrogen-containing crenulide diterpenoids. In a bioassay, compounds , , , and were found to exhibit different levels of inhibitory effects against protein tyrosine phosphatase 1B (PTP1B) with IC values ranging from 7.3 to 19 μM. In addition, the primary structure-activity relationships of all the isolates were summarized.