Chiral insect sex pheromones

Asymmetric syntheses directed toward construction of enantiomers of the western and southern corn root-worm pheromones are described. A brief review of the subject of asymmetric synthesis as it is related to the synthesis of insect sex pheromones is presented. The laboratory s previous research with chiral pheromones is summarized (Japanese beetle, white peach scale, and lesser tea tortrix) before detailing synthetic work on the pheromones of the aforementioned rootworm species. Throughout the course of the synthetic effort, cholesteric stationary phases for GLC have found use. Their superior ability to separate crucial diastereomeric intermediates for synthesis is detailed. 

Laevoglucosenone (27) provides a convenient starting material for a chiral synthesis of the insect sex pheromone serricornin (28) and for (-)-6-multistriatin (29)(Scheme 7), the kinetically formed C-2 axial epimer of the 2,4-di-C-methyl-anhydro sugar intermediate isomerizing to the required C-2 equatorial isomer in acid. ... 

In another example, the organocatalytic a-chlorination was successfully employed to constmct the chiral epoxides in the synthesis of two insect sex pheromones 107 and 108, which were isolated from the pine looper moth Bupalus piniarins and the tussock moth Orgyia postica, respectively. The synthesis of these enantiopure compounds may offer a solution to pest control. 

Pheromones of insect species in the order Coleoptera are characterized by considerable structural diversity. Unlike the lepidopterous sex pheromones, which are nearly all tatty acid derivatives, coleopterous sex pheromone structures range in complexity from the relatively simple 3,5-tetradecadienoic acid of the black carpet beetle to the tricyclic terpenoid, lineatin, of the striped ambrosia beetle. While the sex pheromones of many beetles consist of mixtures of compounds that act synergistically to elicit a behavioral response, other Coleoptera species appear to use only a single compound for chemical communication between the sexes. In the latter case the compound usually has at least one chiral center and chirality plays a major role in determining pheromone specificity. 

Chiral columns are also employed in pheromone research for the determination of the absolute configuration of stereoisomers. The configuration of 4-methylheptan-3-ol and 4-methylheptan-3-one, sex pheromones of the oak bark beetle, were determined using a fused silica column coated with octakis [6-0-methyl-2,3-di-0-pentyl]-7-cyclodextrin. The elution order of the ketone stereoisomers was determined according to the literature and the natural compound was found to be (S)-methylheptanone. The absolute configuration of the alcohol present in the insects was determined by comparison with authentic standards and was found to be (3R, 4S)-methylheptanol. 

The use of GC-EAD allows the rapid screening of compounds and extracts in order to identify those eliciting a response and eliminate those not detected by the insect. GC-EAD takes full advantage of the separation capabilities of GC together with the detection capabilities of the EAD. Stereochemical determination can also be achieved using GC-EAD, and the use of chiral stationary phases allowed the stereochemical identification of the sex pheromone of the brown-banded cockroach. 

Insects have been ideal organisms on which to carry out semiochemical studies and as a majority of their pheromones are volatile or semivolatile they are particularly suited to GC-MS analysis. This, coupled with the slower introduction of LC-MS explains why the use of HPLC in pheromone identification is more limited however, this is changing. A recent report used the greater resolving power of chiral LC compared to chiral GC to directly measure the natural ratio of enantiomers of (Z,Z)-cis-3,4-epoxy-6,9-non-adiene, the female sex pheromone of the Japanese giant looper moth. This article also suggests that with the use of microcolumns LC-MS has the potential to rival GC-MS for sensitivity, thus taking HPLC out of its previous use of prefraction prior to GC-MS analysis and the purification and separation of synthetic pheromones. 

Another interesting situation is the olive fruit fly (Bactrocera oleae). The female produces the sex pheromones J -olean and S-oleanasdrawninFigure4.10 [19]. The J -olean excites males, and the S-olean excites herself One final example of the amazing variety of ways in which insects use chirality is the... 

Rossi, R., and A. Carpita Insect pheromones — synthesis of chiral sex pheromone components of several species of Trogoderma (Coleoptera Dermestidae). Tetrahedron 33,2447—2450(1977). 

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