Nigerin and ochracenes J−L, new sesquiterpenoids from the marine sponge symbiotic fungus Aspergillus niger

Four new sesquiterpenoids, nigerin (1) and ochracenes J–L (2–4), were isolated from a symbiotic fungus Aspergillus niger of a marine sponge Dysidea sp. collected from the South China Sea. Nigerin (1) possesses an unprecedented 1-(3-n-pentyl)-2,5,6-trimethyl-cycloheptane carbon skeleton, which represents a new type sesquiterpene scaffold. Ochracenes J–L (2–4) are three new humulane-derived sesquiterpenoids. The structures of 1–4 were elucidated by a combination of 1D and 2D NMR and HRMS analyses, and their absolute configurations were assigned by Mosher's method and ECD calculations. Among the four isolates, nigerin (1) and ochracene J (2) showed potent inhibitory activity on the production of nitric oxide (NO) in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages with IC50 values of 8.5 and 4.6 μM, respectively.