Clavariopsins C–I, Antifungal Cyclic Depsipeptides from the Aquatic Hyphomycete Clavariopsis aquatica

Seven new cyclic depsipeptides, clavariopsins C–I (3–9), together with two known congeners, clavariopsins A and B (1 and 2), were isolated from the aquatic hyphomycete Clavariopsis aquatica. Their planar structures, which consist of nine amino acids and one α-hydroxy acid, were elucidated by NMR spectroscopy and HRESIMS. The absolute configurations were established by the advanced Marfey’s method and chiral-phase HPLC analysis. Their antifungal and cytotoxic activities were evaluated against six plant pathogenic fungi (Botrytis cinerea, Magnaporthe oryzae, Colletotrichum orbiculare, Fusarium oxysporum, Alternaria alternata, and Aspergillus niger) and a cancer cell line (HeLa-S3), respectively. The majority of the compounds exhibited potent antifungal activity against the fungi tested (minimum inhibition dose = 0.01–10 μg/disk) and induced hyphal swelling in A. niger (minimum effective dose = 0.3–3 μg/disk), whereas the compounds exhibited no cytotoxicity toward the cancer cell line. The results suggest that the clavariopsins could be a promising class of antifungal agents.