Specialized metabolites from Ageratina adenophora and their inhibitory activities against pathogenic fungi.
The Asteraceae plant Ageratina adenophora (also called Eupatorium adenophorum) has became the most destructive invasive species in China, especially the southwestern region, and is gravely threatening the native biodiversity. Its high reproductive capacity is partly due to the developed root system. From the roots of A. adenophora, ten compounds including three previously undescribed benzofuran derivatives (7-hydroxy-dehydrotremetone, 7,10,11-trihydroxy dehydrotremetone, 10-oxo-7-hydroxy-nordehydrotremetone), a previously undescribed chromene derivative (5-β-glucosyl-7-demethoxy-encecalin) and a previously undescribed monoterpene glucoside (8-hydroxy-8-β-glucosyl-2-carene) were isolated and identified. The previously undescribed structures were established by spectroscopic studies including 1D and 2D-NMR and HR-MS analyses. Antifungal activity of six compounds against one strain of pathogenic fungus of A. adenophora, Alternaria alternata, and other four strains of agricultural pathogenic fungi, Colletotrichum gloeosporioides, C. musae, Rhizoctonia solani and Fusarium oxysporum f. sp. niveum were investigated. The most abundant compound we isolated from A. adenophora roots was 7-hydroxy-dehydrotremetone, which showed significant broad-spectral inhibitory activity against the growth of all tested fungal strains, with diameter of inhibitory zones ranging from 13.90±1.05 mm to 17.28±0.46 mm at 50 µg/disk (nystatin: 24.76±1.19 mm to 36.64±0.85 mm). Encecalin also showed weak inhibitory activity against F. oxysporum f. sp. niveum, while other compounds were not active. Our results suggested that 7-hydroxy-dehydrotremetone might function as a constitutive defense compound in the roots of A. adenophora against pathogenic fungi.