Total Synthesis, Stereochemical Assignment, and Field-Testing of the Sex Pheromone of the Strepsipteran Xenos peckii.

The sex pheromone of the endoparasitoid insect Xenos peckii (Strepsiptera: Xenidae) was recently identified as (7E, 11E)-3,5,9,11-tetramethyl-7,11-tridecadienal. Herein we report the asymmetric synthesis of three candidate stereostructures for this pheromone using a synthetic strategy that relies on an sp(3)-sp(2) Suzuki-Miyaura coupling to construct the correctly configured C7-alkene function. Comparison of H-1 NMR spectra derived from the candidate stereostructures to that of the natural sex pheromone indicated a relative configuration of (3R*, 5S*, 9R*). Chiral gas chromatographic (GC) analyses of these compounds supported an assignment of (3R, 5S, 9R) for the natural product. Furthermore, in a 16-replicate field experiment, traps baited with the synthetic (3R, 5S, 9R)-enantiomer alone or in combination with the (3S, 5R, 9S)-enantiomer captured 23 and 18 X. peckii males, respectively (mean +/- SE: 1.4 +/- 0.33 and 1.1 +/- 0.39), whereas traps baited with the synthetic (3S, 5R, 9S)-enantiomer or a solvent control yielded no captures of males. These strong field trapping data, in combination with spectroscopic and chiral GC data, unambiguously demonstrate that (3R, 5S, 9R, 7E, 11E)-3,5,9,11-tetramethyl-7,11-tridecadienal is the X. peckii sex pheromone.