A new cyclic depsipeptide from a fungicolous Hawaiian Isolate of Phaeoacremonium sp

During our continuing studies of fungicolous fungi, an isolate of Phaeoacremonium sp. (NRRL 54515) was obtained from black stromata of a pyrenomycete found on a dead hardwood branch in a Hawaiian forest. Phaeoacremonium is a relatively unexplored fungal genus from a chemical standpoint. The ethyl acetate extract of solid-substrate fermentation cultures of this isolate showed antifungal activity against Fusarium verticillioides. Chemical studies of this extract led to isolation of a new cyclic depsipeptide. The structure of this metabolite was assigned based on analysis of 2D NMR and HRESITOFMSMS data for the compound and its acetylation product. Several N-methyl amino acyl units were present, but the most distinctive structural feature was the incorporation of a five-carbon sugar unit which was identified and located by 2D NMR analysis of the natural product. Its presence and identity were confirmed by GCMS analysis of the corresponding derivatized hydrolysis product in comparison with standards. GCMS analysis of N-trifluoroacetyl-s-butyl ester derivatives of the amino acids obtained upon hydrolysis confirmed the amino acid composition and enabled assignment of their absolute configurations. To our knowledge, this metabolite is the first peptide-type natural product to be reported from a member of the genus Phaeoacremonium.