Fomentarols A–D, sterols from the polypore macrofungus Fomes fomentarius

Eleven sterols were isolated from Fomes fomentarius. Rings A/B and B/C are in turn cis-fused in 2, which is uncommon in natural ergostane-type sterols. Their moderate cytotoxic effects were determined. •Four hitherto unknown ergosterols were isolated from fruiting bodies of Fomes fomentarius.•Compound 2, possessing cis-fused A/B and B/C rings, is an uncommon ergosterol.•Compound 10 exhibited moderate cytotoxicities against A549, MCF-7 and NUGC-3 cells. 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.