Irpexlactones A and B, a pair of ring-rearranged tremulane sesquiterpenoids from the basidiomycete Irpex lacteus and their anti-inflammatory activity

Two unusual sesquiterpenoids, irpexlactones A ( 1 ) and B ( 2 ), were isolated from cultures of the basidiomycete Irpex lacteus . Their structures were established by means of spectroscopic methods, the single crystal X-ray diffraction, as well as electronic circular dichroism (ECD) calculations. They possess a novel carbon skeleton with a 5/6/3-fused ring system that may derive from tremulane type sesquiterpenoids with ring-rearrangement. Both compounds show significant inhibitory activities against nitric oxide production with half maximal inhibitory concentration (IC 50 ) values of 2.2 and 1.4 µmol/L, respectively. Their anti-inflammatory effects were further evaluated by enzyme-linked immunosorbent assay (ELISA) and Western blot. Two unusual sesquiterpenoids, irpexlactones A and B, have been isolated from Irpex lacteus . They possess a novel carbon skeleton with a 5/6/3-fused ring system that may derive from tremulane type sesquiterpenoids with ring-rearrangement. Both compounds show significant inhibitory activities against nitric oxide production with IC 50 values of 2.2 and 1.4 µmol/L.