Receptor assay-guided isolation of anti-GABAergic insecticidal alkaloids from a fungal culture.

The gamma-aminobutyric acid (GABA) receptor bears sites of action for insecticides. To discover GABA receptor-directed insecticides in natural products, fungal culture extracts were screened for their ability to inhibit specific binding of the radiolabeled noncompetitive antagonist [3H]1-(4-ethynylphenyl)-4-n-propyl-2,6,7-trioxabicyclo[2.2.2]octane to housefly head membranes. The screening efforts led to the isolation of two alkaloids from Aspergillus terreus: PF1198A (alantrypinone) and PF1198B (serantrypinone), which had IC50 values of 0.34 and 2.1 microM, respectively, in this assay. These compounds were ca. 47-61-fold selective for housefly vs rat GABA receptors. Both compounds showed insecticidal activity against Myzus persicae in the range of 100-500 ppm. Binding assay-guided screening should provide significant opportunities for the identification of novel and selective insecticides.

SF2809 compounds, novel chymase inhibitors from Dactylosporangium sp. 2. Structural elucidation.

Novel chymase inhibitors, SF2809-I, II, III, IV, V and VI, were isolated from the fermentation broth of Dactylosporangium sp. SF2809, and their structures were determined by spectroscopic analyses. SF2809 compounds commonly contain a substituted indole moiety and a quinolinone moiety. The two moieties are connected to a methylene carbon in SF2809-I and III. The other compounds, SF2809-II, IV, V and VI, have an additional moiety, a p-hydroxyphenyl group or a phenyl group. In these compounds, all of three moieties are connected to a methine carbon. Furthermore, studies concerning the stereochemistry of SF2809-V revealed that the isolated compound was racemic, and the isomer possessing (R)-configuration was about thirty times more potent than another isomer.