Herbicidal and Antifungal Xanthone Derivatives from the Alga-Derived Fungus Aspergillus versicolor D5.

Fungi have been proved as promising and prolific sources of functional secondary metabolites with potent agricultural applications. In this study, 14 xanthone derivatives (1-14), including six new ones, versicones I-N (1-4, 7, 11), and a biogenetically related derivative (15), were isolated from the alga-derived fungus Aspergillus versicolor D5. Their structures were elucidated by comprehensive spectroscopic methods. Versicone L (4) exhibited a broad antifungal spectrum and prominent inhibitory effects on Botrytis cinerea at a minimum inhibitory concentration (MIC) of 152 μM, 7-fold stronger than that of the positive control, carbendazim (MIC = 1.05 × 103 μM). Dihydrosterigmatocystin (13) showed strong antifungal activity toward B. cinerea at MIC = 38.3 μM, almost 30-fold stronger than that of carbendazim. Meanwhile, 13 exhibited potent herbicidal activity toward Amaranthus retroflexus L. with an MIC of 24.5 μM, approximately 4-fold stronger than that of the positive control, glyphosate (MIC = 94.7 μM). Additionally, 13 also displayed remarkable activity against other weeds belonging to Amaranth sp. Analysis of the structure-herbicidal activity relationship indicated that the bifuranic ring played an important role in xanthone phytotoxicity and the presence of a double bond in the furan ring could decrease phytotoxicity. This study indicated that xanthones can be served as promising candidates for lead compounds of agrochemicals.