Chiral pheromones

The authors then used a modification of their Lipase-AK route to produce the natural enantiomer, as described in detail in the chapter by Kenji Mori in this volume. Instead of using the enzyme to execute a stereoselective monohydrolysis of meso diacetate 140, the enzyme was used to esterify selectively one of the hydroxy groups of meso diol 128, resulting in the antipodal hydroxyester. After oxidation of the free hydroxyl to the acid, and recrystallization of its salt with (JR)-l-naphthylethylamine, the purified acid was then carried through the remaining steps to furnish the chiral pheromone compound (see the chapter by Kenji Mori in this volume). 

Leal W. S. (1996) Chemical communication in scarab beetles reciprocal behavioral agonist-antagonist activities of chiral pheromones. Proc. Natl. Acad. Sci. USA 93, 12112-12115. 

Bell, T. W. and Ciaccio, J.A. (1988). Alkylative epoxide rearrangement, application to stereoselective synthesis of chiral pheromone epoxides. Tetrahedron Lett., 29, 865-868. 

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. 

The existence of chirality in pheromone molecules has been recognized since 1966, but as Silverstein (7) explains, most of us ignored it because the insects responded to the synthesized racemic compounds. Thus the insects response to the chiral pheromones identified in earlier work appeared to fall into the first category described by Silverstein (5), i.e., the insect produced and responded to a single enantiomer and the other enantiomer was inactive. Furthermore, the paucity of natural pheromone obtainable from the insects makes it difficult, and in most cases impossible, to determine the stereochemistry of the natural material. 

This is the most common relationship, and the majority (about 70%) of the chiral pheromones belongs to this category. Only the (lR,5S,7R)-isomer of exo-brevicomin (entry 41) is bioactive [207]. (3S,4R)-Faranal (entry 19) is the bioactive enantiomer of the trail following pheromone of the pharaoh s ant [208]. 

Chiral pheromones whose single enantiomers show bioactivity... 

Chiral pheromones whose stereochemistry-bioactivity relationships are diverse and complicated... 

Ashvar CS, Stephens PJ, Eggimann T, Wieser H. Vibrational circular dichroism spectroscopy of chiral pheromones frontalin (l,5-dimethyl-6,8-dioxabicyclo [3.2.1] octane). Tetrahedron Asymmetry 1998 9 1107-1110. 

Chiral 1,3-dialkylallenes. These aUenes can be obtained by reaction of lithium dialkylcuprates with one of the diastereomeric carbamates obtained from racemic secondary propargylic alcohols and the reagent (1). An example is the synthesis of chiral pheromone of the male bean weevil, (R)-( —)-6, as outlined in scheme (I). ... 

Comparison of Racemic and Chiral Pheromone. Lures, replicated 6 times, were loaded with either 25 pg of (5)-(+)-lavandulyl senecioate, or 50 pg of the racemic material. Traps were set out on 21 September and collected on 28 September 2001. Trap counts were compared with a two-sample /-test. 

Having verified the stereoisomeric purity of alcohol 1, a portion was converted to the chiral pheromone, (5)-(+)-lavandulyl senecioate 2a (78% yield), by treatment wiA senecioyl chloride and pyridine in ether 16). 

Figure 4 Experimental (in CCI4) and theoretical (ab initio DFT, B3LYP/6-31G ) spectra of (1R, 5S)-(+)-frontalin (A) absorption spectra, (B) VCD spectra. Reprinted with permission from Ashvar CS, Stephens PJ, Eggimann T and Wieser H (1998) Vibrational circular dichroism spectroscopy of chiral pheromones frontalin (1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane). Tetrahedron Asymmetry S 1107-1110. 1998 Elsevier Science B.V.

Asymmetric acetylation of ( )-40 with vinyl acetate and lipase PS furnished (R)-acetate 41 and (S)-alcohol 40. The former was converted to the axially chiral pheromone of the dried bean beetle (Figure 24.21) [25]. 

The enantiomeric composition of several insect pheromones has been determined by employing a chiral derivative and chiral lanthanide shift reagents (45). The amount of material required was of the order of 5—500 ig of substrate. As the enantiomeric composition of chiral pheromones is of fundamental importance to their efficacy and appears to play a role in speciation, one can expect its determination to become a standard procedure. 

The synthesis of chiral pheromones has been recently reviewed (633). 

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