Eremoxylarins D–J, Antibacterial Eremophilane Sesquiterpenes Discovered from an Endolichenic Strain of Xylaria hypoxylon

An endolichenic strain of the Ascomycetaceous Xylaria hypoxylon, cultivated alone or in coculture with another endolichenic fungus Dendrothyrium variisporum, produced seven new bioactive eremophilane sesquiterpenes eremoxylarins D–J (1–7). The isolated compounds disclosed a high similarity with the eremophilane core of the bioactive integric acid, and structures were elucidated by 1D and 2D NMR spectra and electronic circular dichroism (ECD) analyses. Eremoxylarins D, F, G, and I showed a selective activity against Gram-positive bacteria such as methicillin-resistant Staphylococcus aureus with minimum inhibitory concentration (MIC) values between 0.39 and 12.5 μg/mL. Eremoxylarin I, the most antibacterial active sesquiterpene, was also active against HCoV-229E at a concentration nontoxic to the hepatoma Huh-7 cell line with an 50% inhibitory concentration (IC50) of 18.1 μM and a 50% cytotoxic concentration (CC50) of 46.6 μM.