Antibacterial Activity of Non-Biaryl-Linked Dimeric Tetraxanthones: Insights into Stability and Efficacy against Gram-Positive Bacteria

Aflaxanthone B (1), a non-biaryl-linked dimeric tetraxanthone, was purified from the endophytic fungus Preussia sp. CPCC 401464. Four undescribed transformed products, aflaxanthones C–F (2–5), were obtained by treating compound 1 with dimethyl sulfoxide (DMSO). Their structures were determined by analysis of 1D and 2D NMR spectroscopic data as well as HRESIMS analyses. The absolute configuration of these compounds was established through X-ray crystallographic analysis and ECD calculations. Only compound 1 demonstrated significant antibacterial activity against Gram-positive pathogenic bacteria, suggesting a correlation between the stability of compound 1 and its antibacterial activity.