NEW DESTRUXINS FROM THE ENTOMOPATHOGENIC FUNGUS ASCHERSONIA SP

Two new insecticidal cyclic depsipeptides, destruxins A4 (1) and A5 (2 ), were isolated by bioassay-guided fractionation of organic extracts from an undescribed species of entomopathogenic fungus from the genus Aschersonia. Another previously identified but related compound, homod estruxin B (3), was also isolated as a product of this fungus. The che mical structures of 1-3 were determined based on analysis of NMR and m ass spectral data. In common with homodestruxin B (3), the novel compo unds destruxins A4 (1) and A5 (2) have a MeIle moiety in place of the MeVal residue more typically found in destruxins; In addition, destrux in A5 has a beta-MePro unit in place of the Pro residue found in most destruxins. LC(50) values for 1 and 2 in an insecticidal assay against Drosophila melanogaster were estimated at 41 and 52 ppm, respectively . Homodestruxin B (3) showed no activity at 400 ppm in the same assay. Destruxins A4 (1) and A5 (2) are the first biologically active second ary metabolites reported from the fungal genus Aschersonia, which repr esents a new source of destruxins.