Identification and assignment of the absolute configuration of biologically active methyl-branched ketones from limnephilid caddis flies

Glands of the 4th and 5th abdominal sternite of the caddis flies Potamophyl ax latipennis, Potamophylax cingulatus, and Glyphotaelius pellucidus contai n (S)-4-methyl-3-heptanone (4a), (4S,6S)-4,6-dimethyl-3-octanone (4b), and (4S,6S)-4,6-dimethyl-3-nonanone (4c). As shown by gas chromatography couple d with electrophysiological recordings, these ketones elicit a strong respo nse in the insects' antennae. The structural assignment of the compounds wa s achieved on the basis of mass spectra, enantioselective synthesis, and ga s chromatography on a chiral stationary phase.