Perfluorinated moth pheromones : Synthesis and electrophysiological activity

Perfluoroalkyl analogs of pheromone constituents were synthesized and responses from male antennal olfactory receptor neurons from three moth species were recorded during stimulation by these analogs. In each analog, the hydrophobic terminus, either a butyl or hexyl substituent on the (Z)-alkenyl chain, was replaced with a perfluorobutyl (Pfb, C4F9) or perfluorohexyl (Pfh, C6F13) moiety. Perfluoroalkyl analogs were more volatile than their hydrocarbon analogs, showing a decrease in gas chromatographic retention time by two to four methylene equivalents (Kovàts retention indices). Specialist neurons of maleHeliothis zea responded to a 0.02-μg dose of (Z)-11-hexadecenal (Z11-16∶Al) and a dose of 200 μg of Pfb-Z11-16∶Al with similar spike discharge rates. The HS(a) neurons ofTrichoplusia ni responded to a dose of 0.02 μg ofZ7-14∶OAc and a dose of 10 μg of Pfb-Z7-12∶Ac with similar discharge rates. The same difference in sensitivity to Pfb-Z7-12∶OH andZ7-12∶OH was observed for the responses of the HS(b) neuron and for the responses of theNS(a) neurons to Pfb-Z9-14∶Ac andZ9-14∶Ac. Sensilla ofDiatraea grandiosella similarly showed 100- to 1000-fold greater sensitivity toZ9-16-Al andZ11-16∶Al than to Pfh-Z9-16∶Al and Pfb-Z11-16∶Al. Thus, replacement of terminal alkyl groups with perfluoroalkyl groups in pheromone components produced biologically active compounds with increased volatility and displaced electrophysiological response profiles. Because of the diminished receptor cell sensitivity, we suggest that the binding of the fluorinated analogs to a putative receptor is reduced as a result of less favorable interaction between the hydrophobic protein binding site and the more rigid and more polar perfluoroalkyl moiety.