Laetiporic acids, a family of non-carotenoid polyene pigments from fruit-bodies and liquid cultures of Laetiporus sulphureus (Polyporales, Fungi)

The non-isoprenoid polyene laetiporic acid A, recently described from fruit-bodies of the wood-rotting fungus Laetiporus sulphureus, was found to be the major orange pigment also in mycelium grown in liquid culture. Its formation was variable, ranging from 0.1 to 6.7 mg/g dry weight in three strains, all of which were identified as L. sulphureus by ITS rDNA sequence analysis. A second pigment, 2-dehydro-3-deoxylaetiporic acid A, is also described and fully characterized by NMR spectroscopy. Two further minor pigments, laetiporic acids B and C, were produced in liquid culture. These resemble laetiporic acid A but are enlarged by two and four carbon atoms, respectively, resulting in chromophores with 11 or 12 instead of 10 conjugated double bonds as described for laetiporic acid A. Since fruit-bodies of L. sulphureus are edible, laetiporic acids might hold potential as food colourants.