Taichunamides: Prenylated indole alkaloids from Aspergillus taichungensis (IBT 19404)

Abstract

Seven new prenylated indole alkaloids, taichunamides A-G, were isolated from the fungus Aspergillus taichungensis (IBT 19404). Taichunamides A and B contained an azetidine and 4-pyridone units, respectively, and are likely biosynthesized from notoamide S via (+)-6-epi-stephacidin A. Taichunamides C and D contain endoperoxide and methylsulfonyl units, respectively. This fungus produced indole alkaloids containing an anti-bicyclo[2.2.2]diazaoctane core, whereas A. protuberus and A. amoenus produced congeners with a syn-bicyclo[2.2.2]diazaoctane core. Plausible biosynthetic pathways to access these cores within the three species likely arise from an intramolecular hetero Diels-Alder reaction. Magnificent seven: Seven new prenylated indole alkaloids were isolated from A. taichungensis. This fungus produces alkaloids containing an anti-bicyclo[2.2.2]diazaoctane core, whereas A. protuberus and A. amoenus produce derivatives with a syn-bicyclo core. The structural diversity of tryptophan-derived secondary metabolites reveals unusually diverse stereochemical and structural secondary metabolite tailoring functions in these orthologous fungi.