Three New Secondary Metabolites from Colletotrichum boninense, an Endophytic Fungus in Polygonum multiflorum

Endophytic fungi associated with medicinal plants constitute a promising source of structurally diverse and biologically active natural products. In this study, we investigated the secondary metabolites of Colletotrichum boninense (Strain H10), an endophyte isolated from the medicinal plant Polygonum multiflorum Thunb. A total of 25 secondary metabolites were isolated from rice-based fermentation cultures, among which three were new compounds: one ergosteroid (m1) and two solanapyrone-type polyketides (m2 and m3). The structures were elucidated via comprehensive spectroscopic analyses, including 1D/2D NMR, HRESIMS, ECD calculations, and X-ray crystallography. The known compounds comprised steroids, polyketides, alkaloids, and fatty acids. Phylogenetic analysis based on ITS and LSU sequences revealed that Colletotrichum boninense and related Colletotrichum strains form a distinct clade within the Glomerellaceae. These new solanapyrone and sterol derivatives support the chemotaxonomic significance of this class of compounds in Colletotrichum species. This work enriches the chemical diversity of endophytic fungi derived from Polygonum multiflorum.