The biosynthesis of fulvic acid,a fungal metabolite of heptaketide origin

Analyses of the regiochemistry of [¹³C]acetate incorporation into fulvic acid ($\text{2}$) by Penicillium brefeldianum indicates that the metabolite is biosynthesized via a heptaketide intermediate assembled as a single chain of seven C₂, units rather than from two smaller polyketide chains. This information favours a route leading through common C₁₄ intermediates to the three fungal metabolites, citromycetin, fulvic acid and fusarubin.