Submitted to: Journal of Natural Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 1995
Publication Date: N/A
Interpretive Summary: Microorganisms that can kill insects may provide future alternatives to chemical pesticides. Before we can exploit these insecticidal microorganisms we must understand their ecology and biology, including biochemical compounds they might produce. Some fungi in the genus Aschersonia cause disease in insects and are potential biological control agents. So far, no member of this genus has been reported to produce insecticidal or fungicidal compounds. Now we report that an undescribed species of the genus Aschersonia produces two new compounds, destruxin A4 and A5. These compounds were shown to possess insecticidal properties. These compounds may offer natural alternatives to synthetic pesticides currently in use and may make strains that produce them more effective as biological control agents with the capacity to kill their host insects more rapidly.
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, homodestruxin B (3), was also isolated as a product of this fungus. The chemical structures of 1-3 were determined based on analysis of nmr and mass spectral data. In common with homodestruxin B (3), the novel compounds destruxins A4 and A5 have an MeIle moiety in place of the MeVal residue more typically found in destruxins. In addition, destruxin A5 has a b-MePro unit in place of the Pro residue found in most destruxins. LC50 values for destruxins A4 and A5 in an insecticidal assay against Drosophila melanogaster were estimated at 41 and 52 ppm, respectively. Homodestruxin B showed no activity at 400 ppm in the same assay. Destruxins A4 and A5 are the first biologically-active secondary metabolites reported from the fungal genus Aschersonia, which represents a new source for destruxins.