Examination of Potential Exceptions to the F and S Biosynthetic Classification of Fused‐Ring Aromatic Polyketides

The reported acetate‐derived labelling of the fungal naphthalene γ‐pyrone fonsecin, two streptomycete dodecaketide αpyrones TW93f and TW93g, and the streptomycete phenanthraquinones piloquinone, murayaquinone and haloquinone appear to be exceptions to the generalisation that fungi and streptomycetes produce fused‐ring aromatic polyketides by different modes of cyclisation. A review of their 1) originally assigned formulae, 2) [ 13 C 2 ]acetate‐derived labelling patterns, and 3) modes of cyclisation leads to the recognition of feasible alternative chemical structures or biosynthetic pathways, which are in accord with the originally proposed classification system.