The aphid sex pheromone cyclopentanoids: synthesis in the elucidation of structure and biosynthetic pathways

Identification of a range of aphid sex pheromones as comprising the cyclopentanoids (4aS,7S,7aR)-nepetalactone, (1R,4aS,7S,7aR)-nepetalactol and the (1S)- and (1R,4aR,7S,7aS)-nepetalactols required samples authenticated by 1H and 13C NMR. These and related compounds were provided by small scale synthesis and extraction from plants in the genus Nepeta (Lamiaceae). The subsequent discovery that the synthetic sex pheromones could attract males, and also parasitic wasps that attack aphids, has created a need for large scale syntheses of the cyclopentanoids. This is afforded by cyclisation of the 8-oxo-1-enamine of citronellal as originally developed by Schreiber and co-workers (1986). Investigation into the biosynthesis of the cyclopentanoids by plants for exploiting aphid sex pheromones in crop protection by means of molecular biology required synthesis of putative biosynthetic intermediates, some with radioactive isotopic labelling, particularly 8-oxidised monoterpene alcohols and aldehydes. Aphid sex attractant pheromones comprise the cyclopentanoids 1, 15, 16 and 17. Synthesis based on work by Schreiber and coworkers (1986) provides for large scale field requirements. Biosynthethic and molecular biological studies employ synthetic acyclic precursors, some 3H-radiolabelled.