Chaetochromone A, a 6/6/5 tricyclic chromone derivative from an endophytic fungus Chaetomium sp. SG-01

Chaetochromone A (1), a novel 6/6/5 tricyclic chromone derivative, along with two known naphtho-γ-pyrones, chaetochromins A and B (2 - 3), was isolated from the fermentation of Chaetomium sp. SG-01, an endophytic fungus obtained from the fibrous roots of Schisandra glaucescens Diels. The structures of these compounds, including their absolute configurations, were elucidated by comprehensive analyses of their 1D and 2D NMR, HRESIMS, and single-crystal X-ray crystallography. Compound 1 features a chromone core fused to a five-membered lactone at C-8 and C-12, forming a unique 6/6/5 fused tricyclic ring system. Biological evaluation indicated that compound 1 was inactive in both immunosuppressive and cytotoxicity assays, including concanavalin A (ConA)-stimulated T cell and lipopolysaccharide (LPS)-stimulated B cell proliferation, as well as against three human cancer cell lines (HCT116, MCF-7, and HT-29).