3-substituted-γ-pyrone conjugated ergosterol hybrid with fungicidal activity and potential mechanisms

The increasing fungicide resistance in pathogenic fungi presents a serious challenge to global agricultural production and food security. Phytopathogens like Penicillium italicum and Colletotrichum musae are great threats to economically important crop production. Citrus, a globally important fruit crop, is highly susceptible to post-harvest infections by P. italicum, while the huge post-harvest losses of bananas (Musa spp.) suffer from anthracnose caused by C. musae. In this study, aspergopyranoid A (1), a new γ-pyrone-ergosterol hybrid with a 6/6/6/6/5/6 hexacyclic skeleton, was isolated and identified from the scaled fermentation of mangrove endophytic fungus Aspergillus niger SCNU-F0052. Its structure was unambiguously established by extensive spectroscopic methods, including NMR, MS, and single-crystal X-ray diffraction. Antifungal bioassays indicated that aspergopyranoid A (1) displayed potent inhibitory activity against pathogenic fungi, P. italicum and C. musae with MIC values of 12.5 μg/mL and 6.25 μg/mL, respectively. Further morphological and biochemical investigations revealed that compound 1 may exert its fungicidal effect by disrupting fungal cell wall/membrane integrity and disturbing intracellular redox homeostasis. Transcriptome analysis of P. italicum suggests potential regulatory roles in multiple metabolic pathways and signal transduction. Based on the consistent phenotypic responses between P. italicum and C. musae, these findings provide preliminary mechanistic insights into the antifungal activity of aspergopyranoid A (1), which appears to be a promising lead compound for developing novel agricultural fungicides against these two pathogens.