Determination of the enantiomeric composition of (R*, S*)-1-ethylpropyl 2-methyl-3-hydroxypentanoate, the male-produced aggregation pheromone of Sitophilus granarius

The enantiomeric composition of sitophilate, the granary weevil [Sitophilus granarius (L.)] male-produced aggregation pheromone [(R*,S*)-1-ethylpropyl 2-methyl-3-hydroxypentanoate)], was determined by three methods: (1) bioassaying the synthetic (2S,3R) and (2R,3S) enantiomers of the active (R*,S*) diastereomer; (2) 1H NMR spectroscopy of Mosher ester derivatives of the natural pheromone and synthetic (2S,3R)- and (2R,3S)-sitophilate; and (3) capillary GLC comparisons of the retention times of derivatized natural pheromone and the two synthetic enantiomers. The combined methods confirmed the (2S,3R) enantiomer as the active form of sitophilate. Male granary weevils were shown to produce > 96 % (2S,3R)-sitophilate. No significant attraction of S. granarius by the (2R,3S) enantiomer was observed. Rice and maize weevils [S. oryzae (L.) and S. zeamais Motschulsky] were not attracted by (2S,3R)-sitophilate. Resume Determination chirale de la pheromone d'agregation mâle de Sitophilus granarius: (R*,S*)-1-ethylpropyl 2-methyl-3-hydroxypentanoate S. granarius L. est un depredateur important des grains stockes. Le (R*,S*)-1-ethylpropyl 2-methyl-3-hydroxypentanoate a ete identifie en 1987 comme le principal compose du sitophilate, la pheromone mâle d'agregation de S. granarius. La composition enantiometrique du sitophilate a ete determinee par 3 methodes: 1)  tests biologiques des enantiomeres synthetiques (2S,3R) et (2R,3S) du diastereomere actif (R*,S*); 2)  spectrometrie RMN 1H des esters Mosher derives de la pheromone naturelle et des sitophilates de synthese (2S*,3R*)- et (2R*,3S*); 3)  comparaison en capillarite GLC des temps de retention des derives naturels de la pheromone et des 2 eniantiomeres de synthese. La combinaison des 3 methodes confirme que le (2S,3R) enantiomere est la forme active du sitophilate. Le mâle produit > 96% de l'enantio-mere (2S,3R). Il n'y a pas eu attraction de S. granarius par le (2R,3S) sitophilate. S. oryzae L. et S. zeamais Motsch n'ont pas ete attires par le (2S,3R)-sitophilate. L'utilisation du (2S,3R)-1-ethylpropyl 2-methyl-3-hydroxypentanoate dans des pieges devrait permettre une detection precoce de la presence de S. granarius dans des stocks de grains.