Secondary metabolites from the endophytic fungus Trichoderma afroharzianum and their cytotoxic activities

Twenty-two compounds (1-22) were isolated from the culture of Trichoderma afroharzianum, a strain isolated from the root of Hylomecon japonica. Among them, five undescribed compounds, namely (±)-trichoderchromone A ((±)-1), trichoderchromone B (2), phosteoid B (6), trichodersterol A (7), and trichocalamin A (17), were structurally elucidated, while the remaining seventeen known compounds were identified. The planar structures of the undescribed compounds were characterized by extensive spectroscopic methods, including HRESIMS, UV, IR, and NMR analyses, and their stereochemical features were established by single-crystal X-ray diffraction analysis or comparison of experimental and calculated ECD spectra, as appropriate. Notably, (±)-1 was obtained as a racemic mixture, as indicated by its near-zero optical rotation and crystallization in the centrosymmetric space group Pbcn. Subsequently, the cytotoxic activities of all compounds were investigated in vitro using human tumor cell lines. The cytotoxicity screening showed that compounds 7, 9 and 11 exhibited inhibitory activities against the human gastric adenocarcinoma cell line AGS and the human gastric carcinoma cell line HGC-27. Compound 7 showed IC₅₀ values of 46.7 and 58.1 μM against AGS and HGC-27 cells, respectively, while compounds 9 and 11 showed IC₅₀ values of 9.8 and 9.6 μM against AGS cells and 16.9 and 27.2 μM against HGC-27 cells, respectively.