(+)-Austrocorticin and austrocorticinic acid, the first anthraquinones derived from a propionate-triggered octaketide

The toadstool pigments (1) and (2) bearing a unique C2 side chain at C-3 in the anthraquinone nucleus have been isolated and characterised and their biogenesis studied by feeding 13C labelled precursors to young fruit bodies; high specific incorporation of label from sodium [3-13C]propionate into the C-3′ methyl group of (1) indicates a clear propionate ‘starter’ effect is operating.