Configurational Assignment of Malfilamentoside A and a New Furanone Glycoside Malfilamentoside D

High performance liquid chromatography-diode array detection (HPLC-DAD)-based chemical analysis of the extract fraction library of the plateau soil-derived fungus Auxarthron umbrinum SCSIO 40432 led to the identification of eight compounds, including a known aromatic furanone glycoside malfilamentoside A (1) whose stereochemistry remained unsolved, and a new malfilamentoside D (2), together with six known compounds (3 similar to 8). The planar structures of malfilamentaosides A (1) and D (2) were elucidated by HRESIMS, 1D and 2D NMR spectroscopic analysis. The absolute configuration of malfilamentoside A (1) was unambiguously resolved for the first time by a single crystal X-ray diffraction analysis and the stereochemistry of malfilamentoside D (2) was determined by comparing electronic circular dichroism (ECD) spectra of 1 and 2. Malfilamentoside A (1) exhibited inhibitory activity to xanthine oxidase at the concentration of 20 mu mol/L.