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.