Discovery of Oosporein as a New Inhibitor of Influenza Virus Cap-snatching Activity

During our screening of microbial origins, we found that fungal strain BF-0073 produces an inhibitor of the cap-snatching activity of influenza virus. Compound (1) was isolated from the culture broth of fungal strain BF-0073 by solvent extraction and preparative HPLC. Based on structural analyses using MS and NMR, 1 was identified as oosporein. Compound 1 inhibited the cap-snatching activity of influenza virus A in a dose-dependent manner, with an IC50 value of 20.0 μg/mL.