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A phytochemical investigation of an East China Sea collection of the brown alga Dictyota coriaceahas 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 7were found to exhibit different levels of inhibitory effects against protein tyrosine phosphatase 1B (PTP1B) with IC50values ranging from 7.3 to 19 μM. In addition, the primary structure–activity relationships of all the isolates were summarized.

Two novel rearranged Diels–Alder adducts, morunigrines A (1) and B (2), and four new prenylated flavonoids, morunigrols A–D (3–6), were isolated from the twigs of Morus nigra, together with four known prenylated phenolic compounds, including two flavonoids (7and 8) and two 2-arylbenzofurans (9and 10). Morunigrines A (1) and B (2) are a novel class of Diels–Alder adducts with unprecedented carbon skeletons featuring a rearranged chalcone–stilbene/2-arylbenzofuran core decorated with a unique methylbiphenyl moiety. The structures of the new compounds were assigned by analysis of spectroscopic data. The absolute configuration of compound 6was determined by the measurement of specific rotation. A plausible biogenetic pathway for 1and 2is also proposed. Compounds 1and 2exhibited more potent protein tyrosine phosphatase 1B inhibitory activity with IC50values of 1.8 ± 0.2 and 1.3 ± 0.3 μM, respectively, than that of the positive control oleanolic acid (IC50, 2.5 ± 0.1 μM).