(±)-Talapyrones A−F: six pairs of dimeric polyketide enantiomers with unusual 6/6/6 and 6/6/6/5 ring systems from Talaromyces adpressus

(±)-Talapyrones A−F (1−6), six pairs of dimeric polyketide enantiomers with unusual 6/6/6 and 6/6/6/5 ring systems, were isolated from the fungus Talaromyces adpressus. Their structures were determined by spectroscopic methods and HR-ESI-MS data, and their absolute configurations were further elucidated by a modified Mosher’s method and electronic circular dichroism (ECD) calculations. (±)-Talapyrones A−F (1−6) possess a 6/6/6 tricyclic skeleton, which is possibly constructed by a Michael addition reaction between one molecule of α-pyrone derivative and one molecule of C₈ poly-β-keto chain. In addition, compounds 2/3 and 4/5 are two pairs of C-18 epimers, respectively. Putative biosynthetic pathways of 1−6 were discussed.