New phomactin analogues from an unidentified fungicolous fungal isolate obtained from the surface of a polypore

Abstract

Our ongoing search for new bioactive natural products from fungicolous fungi led to investigation of the ethyl acetate extract of cultures of an undetermined dematiaceous fungus (MYC-1907) obtained from the surface of a polypore found on a dead hardwood branch collected in Lava Tree State Park, Hawaii. The extract showed antifungal activity against Aspergillus flavus and antiinsectan activity against fall armyworm. Chemical investigation of this extract led to the isolation of six new phomactin analogues, in addition to four known compounds (phomactins F, I, and J and epi-phomactin I). Previously reported phomactins have shown potent activity as platelet activating factor (PAF) antagonists. The groß structures of the new analogues were established using various 1D and 2D NMR techniques. Relative configurations were established by interpretation of NOESY data, and absolute configurations were assigned using X-ray diffraction analysis and/or electronic circular dichroism (ECD) in conjunction with computational methods. Absolute configurations of three additional new phomactin analogues isolated in our lab from an extract of different isolate (Mycelia sterilia MYC-1969) were also proposed by analysis of their ECD spectra. One of the latter phomactins showed significant antifungal activity against A. flavus and antibacterial activity against Escherichia coli and Staphylococcus aureus.