Identification of the antibiotic phomalactone from the entomopathogenic fungus Hirsutella thompsonii var. synnematosa

Dichloromethane extracts of culture broth from three strains of the entomopathogenic fungus Hirsutella thompsonii var. synnematosa were toxic to two species of tephritid fruit fly and inhibited conidial germination in vitro in several other entomopathogenic fungi including Beauveria bassiana, Tolypocladium spp., and Metarhizium anisopliae. A major metabolite, toxic to apple maggot, Rhagoletis pomonella, and inhibitory to conidial germination in B. bassiana, was isolated and identified as the antibiotic (+)-phomalactone, 6-(1-propenyl)-5,-6-dihydro-5-hydroxypyran-2-one. This is the first biologically active compound of low molecular weight isolated from the genus Hirsutella