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Two independently biologically active compounds, periplanone A and periplanone B can be isolated from fecal material of the American cockroach,Periplaneta americana. In fecal material these occur in a ratio of 1 ∶ 10 while, in intestinal tracts only periplanone B has been found. The latter has been identified as (1Z,5E)-1,10(14)-diepoxy-4(15),5-germacradien-9-one; the identification was confirmed by synthesis. Only the CD (-) enantiomer (1R,2R,5E,7S,10R) exhibited activity. The lower threshold of activity of both natural and synthetic CD (-) pheromone, is 10(-6)-10(-7) μg. Periplanone A has been identified (apart from its stereochemical configuration) as 7-methylene-4-isopropyl-12-oxa-tricyclo[4.4.2.0(1,5)]-9-dodecen-2-one). The structure of this rather unstable compound could be deduced by comparing its NMR, UV, IR, and mass spectra with the NMR and mass spectra of its rearrangement product. Both structures still require confirmation by synthesis, but their spectral data are in complete agreement with the proposed structures. The presence of only periplanone B in the gut and the presence of both periplanone A and periplanone B in the feces suggests that periplanone B is a genuine sex pheromone, whereas peri-planone A might be a biologically active transformation product, which in turn can isomerize into a more stable, but inactive compound.