Fomentarols A-D, sterols from the polypore macrofungus Fomes fomentarius.

Four (1-4) hitherto unknown and seven (5-11) known ergostane-type sterols were isolated from the EtOH extract of the dried fruiting bodies of the polypore macrofungus Fomes fomentarius. On the basis of spectroscopic analysis, the structures of polyhydroxylated sterols 1-4 were elucidated to be (22E,24R)-3β,5α,6β,14α-tetrahydroxyergosta-7,9(11),22-triene (fomentarol A, 1), (22E,24R)-3β,5β,6α,7α-tetrahydroxy-8α,9α-dihydroergosta-14,22-diene (fomentarol B, 2), (22E,24R)-3β,5α-dihydroxy-6β-ethoxyergosta-7,22-diene (fomentarol C, 3), and (22E,24S)-3β,25-dihydroxy-15α-O-β-D-glucopyranosylergosta-7,22-dien-6-one (fomentarol D, 4), respectively. Rings A/B and B/C are in turn cis-fused in compound 2, which is uncommon in natural ergostane-type sterols. The potential biogenetic relationship of 2 and other ergostane-type sterols isolated from F. fomentarius was briefly discussed. Moderate cytotoxic effects of the isolated sterols against a small panel of human cancer cell lines were also established.