Unusual polyketides from the wood-decay fungus Sistotrema raduloides

The metabolites of the wood rot decay fungus Sistotrema raduloides (P Karst) Donk have been investigated and a new type of norpentaketide has been discovered. The compounds sistodiolynne (1), sistolynone (5), and sistopyrone (6) represent new carbon skeletons among natural products. The compounds are very unstable and readily polymerize in the presence of air to give black insoluble material. It has been shown by C-13 NMR labelling experiments that they arise from five acetate units, and that a methyl carbon of one of the acetate units is lost during the biosynthesis. The structures were determined by spectroscopy methods, mainly NMR, and the absolute configuration of sistodiolynne was established by circular dichroism methods.