Six undescribed sesquiterpenoids from the endophytic fungus Irpex lacteus: Their antifungal and inhibitory activities against Setaria viridis.

Twelve sesquiterpenoids, comprising six new compounds (1-6) and six known compounds (7-12), were isolated from the endophytic fungus Irpex lacteus derived from Castanea mollissima Blume. Structural elucidation was achieved through a combination of spectroscopy, ECD calculations, and X-ray crystallography. These compounds exhibited diverse antifungal activities against Fusarium equiseti. Compound 7 displayed antifungal activity against F. equiseti with a MIC of 2 μg/mL, which was comparable to the positive control nystatin (1 μg/mL). Compared with all the tested compounds, compound 3 at 60 μg/mL exerted the strongest inhibitory effect on the shoot growth of Setaria viridis seedlings, with an inhibition rate of 82%. For the root growth of S. viridis seedlings, compound 9 at 30 μg/mL showed the highest inhibitory activity, reaching an inhibition rate of 94%. These findings highlight the metabolic diversity of I. lacteus and provide valuable insights into the development of antifungal agents against F. equiseti and herbicides against S. viridis.