Mycousfurans A and B, Antibacterial Usnic Acid Congeners from the Fungus Mycosphaerella sp., Isolated from a Marine Sediment

Mycousfurans ( and ), two new usnic acid congeners, along with (-)-mycousnine ( ), (-)-placodiolic acid ( ), and (+)-usnic acid ( ), were isolated using high-performance liquid chromatography-ultraviolet (HPLC-UV)-guided fractionation of extracts of sp. isolated from a marine sediment. The planar structures of and were elucidated using 1D and 2D NMR spectra. The relative configurations of the stereogenic carbons of and were established via analysis of their nuclear Overhauser spectroscopy (NOESY) spectra, and their absolute configurations were determined using a comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compounds and were found to have antibacterial activity, showing moderate activity against and .