Xylaricins A-I: Dearomatic xanthone derivatives from endolichenic fungus Xylaria sp. LCSS1a.

Chemical investigation of the ethyl acetate extract of the endolichenic fungus Xylaria sp. LCSS1a resulted in the isolation and identification of 24 natural metabolites. Among them, 15 were known compounds and 9 of them were characterized as previously unreported dearomatized xanthone derivatives with highly oxygenated substituents, which were designated as xylaricins A-I (1-9). The structures and absolute configurations of the previously unreported compounds were elucidated through extensive spectroscopic analysis, quantum chemical calculations (C NMR DP4+ analysis, and TDDFT-ECD) and X-ray crystallography. The screening for cytotoxic and antibacterial assays revealed that compound 9 exhibited moderate inhibitory activity against A549 lung cancer cells, with an IC value of 7.5 μM, while to Staphylococcus aureus, the MIC value was 16 μg/mL. Structure-activity relationships highlighted the importance of a conjugated π-system and free phenolic groups for bioactivity observed in this series.