Secondary Metabolites Produced by an Endophytic Fungus Pestalotiopsis sydowiana and Their 20S Proteasome Inhibitory Activities

Fungal endophytes have attracted attention due to their functional diversity. Secondary metabolites produced by Pestalotiopsis sydowiana from a halophyte, Phragmites communis Trinus, were investigated. Eleven compounds, including four penicillide derivatives (1–4) and seven α-pyrone analogues (5–10) were isolated from cultures of P. sydowiana. The compounds were identified based on spectroscopic data. The inhibitory activities against the 20S proteasome were evaluated. Compounds 1–3, 5, and 9–10 showed modest proteasome inhibition activities, while compound 8 showed strong activity with an IC50 of 1.2 ± 0.3 μM. This is the first study on the secondary metabolites produced by P. sydowiana and their proteasome inhibitory activities. The endophytic fungus P. sydowiana might be a good resource for proteasome inhibitors.