The structures of five new didehydropeptides related to neoechinulin, isolated from Aspergillus amstelodami

Abstract

Five new neoechinulin-type metabolites have been isolated from the mycelium of Aspergillus amstelodami, grown on molasses beet cultures. They are all characterised by a didehydrotryptophyl structure with a reversed isoprenic chain at the 2-position of the indole nucleus, and have been named neoechinulins A–E. On the basis of chemical and spectral evidence they have been shown to be, respectively, cyclo-alanyl-2-(1,1-dimethylprop-2-enyl)-didehydrotryptophyl (II), cyclo-didehydroalanyl-2-(1,1-dimethylprop-2-enyl)didehydrotryptophyl (III), cyclo-didehydroalanyl-2-(1,1-dimethylprop-2-enyl)-6-(3-methylbut-2-enyl)didehydrotryptophyl (IV), cyclo-alanyl-2-(1,1-dimethylprop-2-enyl)-6-(3-methylbut-2-enyl)didehydrotryptophyl (V), and cyclo-oxamyl-2-(1,1-dimethylprop-2-enyl)didehydrotryptophyl (VI).