Diplobifuranylones A and B, 5�-monosubstituted tetrahydro-2H- bifuranyl-5-ones produced by Diplodia corticola, a fungus pathogen of cork oak

Two new 5'-monosubstituted tetrahydro-2H-bifuranyl-5-ones, named diplobifuranylones A (I) and its stereoisomer, B were isolated from the culture filtrates of Diplodia corticola, the causal agent of a canker of cork oak (Quercus suber). The same fungus also produced 8 known metabolites, namely, the diplopyrone, (3S,4R)-trans- and (3R,4R)-cis-4-hydroxymellein, sapinofuranone B and its (S,S)-diastereomer, and sphaeropsidins A-C. They were characterized, using spectroscopic and chem. methods, as 2 diastereomeric 5'-(1-hydroxyethyl)-3,4,2',5'-tetrahydro-2H-[2,2']bifuranyl-5-ones. While the relative stereochem. of the 2 metabolites was deduced by NOESY and ROESY expts., the abs. stereochem. of the chiral C of the hydroxyethyl side chain at C-5', detd. by application of Mosher's method, proved to be S and R in them, resp. Assayed on a nonhost plant, they did not show phytotoxic activity. In an Artemia salina larvae lethality bioassay neither were toxic at the highest concn. tested (300 g/mL).