Discovery of antimicrobial anthraquinones with membrane-damaging effects from endophytic fungus Stagonosporopsis sp.

Three new anthraquinone derivatives, stagonoquinones A−C (1−3), along with 11 known analogues, were isolated from the endophytic fungus Stagonosporopsis sp. YZHH-J-1 guided by a bioactivity-guided approach combined with HSQC-based DeepSAT analysis. Their structures were established by comprehensive spectroscopic analysis, NMR calculations combined with statistical protocols (CP3 and DP4+ analysis), and optical rotation calculations. Antimicrobial evaluation revealed that compounds 1, 5, 8, 11, and 13 exhibited moderate inhibitory effects against six strains of Cryptococcus gattii, with MIC values of 32−64 μg/mL. In addition, compounds 1, 2, 7, and 11 exhibited antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, and Bacillus subtilis, with MIC values of 8−32 μg/mL. Mechanistic studies indicated that compound 1 inhibited MRSA by inhibiting biofilm formation, increasing membrane permeability and inducing reactive oxygen species (ROS) accumulation. Furthermore, network pharmacology and molecular docking identified dihydrofolate reductase (DHFR) as a potential target of compound 1 for its antibacterial effect. These findings not only enrich the structural diversity of anthraquinones but also provide promising lead candidates for antimicrobial agents.