Four new sesquiterpenoids from fruiting bodies of the fungus Inonotus rickii.

Three new bisabolane sesquiterpenoids, inonotic acid A (1), 3-O-formyl inonotic acid A (2), inonotic acid B (3), and one new drimane sesquiterpenoid 3α,6β-dihydroxycinnamolide (4), were isolated from the fruiting bodies of mushroom Inonotus rickii. Their structures were elucidated by means of extensive spectroscopic methods. Compound 4 had moderate inhibitory activity on human colon cancer SW480 (IC50 = 20.4 μmol).