The Metabolites Produced by Citrus reticulata-Derived Endophyte Aspergillus fumigatus as Potential Antifungal Agents Against Citrus Pathogens.

Six new bergamotene sesquiterpenoids (1-6), one new cyclohexenone derivative (7), and nine known compounds (8-16) were isolated from Citrus reticulata-associated endophytic fungus Aspergillus fumigatus. The structures were systematically established mainly by NMR data, HRESIMS, DP4+ analysis, and ECD calculations. Compounds 2-6 were proposed to be derived from β-trans-bergamotene via C-5/C-6 skeletal cleavage and further modifications. Among them, compounds 2 and 3 represent the first reported instances of the β-bergamotene derivatives bearing an epoxide moiety, characterized by unique 6/5/3 and 6/6/3 tricyclic frameworks based on oxabicyclo[3.2.1]octane and oxabicyclo[3.3.1]nonane cores, respectively. Antifungal activities against two citrus pathogens, Fusarium graminearum and Alternaria alternata, revealed that most compounds exhibited significant antifungal activities, with MIC values of 1-8 µg/mL. Notably, the antifungal activities of compounds 8 and 9 against A. alternata and compound 14 against F. graminearum were comparable to those of nystatin.