Streptoglycerides E–H, Unsaturated Polyketides from the Marine-Derived Bacterium Streptomyces specialis and Their Anti-Inflammatory Activity

Four new streptoglycerides E–H (1–4), with a rare 6/5/5/-membered ring system, were isolated from a marine-derived actinomycete Streptomyces specialis. The structures of 1–4 were elucidated by detailed analysis of HRESIMS, 1D and 2D NMR data and ECD spectra as well as comparison of their spectroscopic data with those reported in literature. Compounds 1–4 showed significant anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced nitric oxide (NO) production in Raw 264.7 cells with IC(50) values ranging from 3.5 to 10.9 µM. Especially, 2 suppressed mRNA expression levels of iNOS and IL-6 without cytotoxicity.