Isocoumarins from the fermentation products of a plant entophytic fungus Penicillium oxalicum

Three new isocoumarins, terrecoumarins A–C (1–3), together with six known isocoumarins (4–9) were isolated from the fermentation products of the fungus Penicillium oxalicum 0403. Their structures were elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques. The anti-tobacco mosaic virus (anti-TMV) activities of 1–9 were evaluated. The results revealed that compound 1 showed high anti-TMV activity with inhibition rate 25.4 ± 3.5%. Other compounds also showed weak activity with inhibition rate in the range of 11.3–18.9%.