Submitted to: Journal of Natural Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2011
Publication Date: June 1, 2011
Citation: Khrimian, A., Cosse, A.A., Crook, D.J. 2011. Absolute configuration of 7-epi-sesquithujene. Journal of Natural Products. 74(6):1414-1420.
Interpretive Summary: Insect pests cause significant damage to crops and forests, and monitoring their populations aids greatly in reducing pesticide use and biological control. Emerald ash borer is an invasive insect species established recently in North America that destroys a variety of ash trees. A volatile attractant is needed to monitor populations of emerald ash borer in low infestation areas. There is an indication in the literature that a plant-produced chemical (called 7-epi-sesquithijene) could be used as an attractant. However, this natural compound can exist in four different structural forms, and in the current manuscript we established what that structural form is. Our finding will help in devising a synthetic route to make this chemical available for field testing against emerald ash borer. The results of this study are of interest to other chemists and entomologists involved in research on potential pest control compounds, and to State and Federal agencies involved in monitoring and controlling emerald ash borer.
7-epi-Sesquithujene is a bicyclic sesquiterpene isolated from the Phoebe oil, essential oil of the Brazilian walnut tree, Phoebe porosa. It is also produced by stressed ash trees and has been shown to elicit strong electrophysiological responses on emerald ash borer, Agrilus planipennis, antennae. In the course of development of a synthetic 7-epi-sesquithujene for field testing against the emerald ash borer, we found that the absolute configuration of this compound had not been determined. We isolated >95%-pure 7-epi-sesquithujene from the Phoebe via successive fractionation, conventional and argentation (HPLC) chromatographies. We found that the specific optical rotation of this compound matches the one of a synthetic product of a known stereostructure. We also synthesized two other diatereomers of sesquithujene and developed a chiral GC method to separate all four stereoisomers. Based on the specific rotation, stereoselective syntheses and chiral GC analyses, 7-epi-sesquithujene present in the Phoebe oil and white ash was found to be (1S,5S)-5-[(1'R)-1',5'-dimethyl-4'-hexenyl]-2-methylbicyclo[3.1.0]hex-2-ene ((1S,5S,1'R)-1).