Meroterpenoid Pigments from the Basidiomycete Albatrellus ovinus

Eight grifolin derivatives, involving three new monomers, albatrelins A–C (1–3), three novel dimers (meroterpenoid pigments), albatrelins D–F (4–6), and two known ones, 6a,7,8,9,10,10a-hexahydro-3,6,9-trimethyl-6-(4-methyl-3-penten-1-yl)-1,9-epoxy-6H-dibenzo­[b,d]­pyran (7) and confluentin (8), were isolated from Albatrellus ovinus. Their structures were established by extensive spectroscopic analysis. The absolute configurations of compounds 2–4 were determined as 9R by comparing their optical rotations with data reported in the literature. Albatrelin F (6) was isolated as a pair of C-2′ tautomers with a ratio of 1.3:1. Confluentin (8) showed weak cytotoxicity against four human tumor cell lines, HL-60, SMMC-7712, A-549, and MCF-7, in vitro.