Antifungal activities of triterpenoids from the roots of Astilbe myriantha Diels

During a search for plant extracts that possess activity against the fungi that cause diseases in plants, a 95% ethanol extract from the roots of Astilbe myriantha Diels showed inhibitory activity against Colletotrichum gloeosporioides. Bioassay-guided fractionation of the 95% ethanol extract led to the isolation of seven triterpenoids (1–7). Their structures were elucidated by spectroscopy and by a comparison with literature data. Among these compounds, 3β,6β,24-trihydroxyurs-12-en-27-oic acid (7) was the most active inhibitor of C. gloeosporioides, with >68.0% inhibition at 100 mg/ml after 72 h. Moreover, compound 7 displayed broad-spectrum inhibitory activity against Rhizoctonia solani, Fusarium oxysporum f. sp. Niveum, Fusarium oxysporum f. sp. Cubens, C. gloeosporioides, Penicillium citrinum, Colletotrichum lagenarium, and Penicillium digitatum, with EC50 values ranging from 13.9 to 34.0 μg/ml. The potential of compound 7 as a fungicide is therefore promising. In addition, compound 1 was found to be a new triterpenoid, 3β,6β-dihydroxyurs-12-en-7α,27α-olide, which possesses six rings.