An epigenetic modifier induces production of 3-(4-oxopyrano)-chromen-2-ones in Aspergillus sp. AST0006, an endophytic fungus of Astragalus lentiginosus

Incorporation of the epigenetic modifier suberoylanilide hydroxamic acid (SAHA) into a potato dextrose broth culture of the endophytic fungus Aspergillus sp. AST0006 affected its polyketide biosynthetic pathway providing two new 3-(4-oxopyrano)-chromen-2-ones, aspyranochromenones A (1) and B (2), and the isocoumarin, (−)-6,7-dihydroxymellein (3). Eight additional metabolites (4–11) and two biotransformation products of SAHA (12–13) were also encountered. The planar structures and relative configurations of the new metabolites 1–2 were elucidated with the help of high-resolution mass, 1D and 2D NMR spectroscopic data and the absolute configurations of 1–3 were determined by comparison of experimental and calculated ECD data. Possible biosynthetic pathways to 1 and 2 are presented.