Pheromones bioactivity relationships

By synthesizing pure enantiomers of pheromones, various stereochemistry-pheromone activity relationships could be clarified. For example, in the case of sulcatol (6-methyl-5-hepten-2-ol),both the enantiomers are necessary for bioactivity. For other relationships, please refer to [4-9]. 

It was clear in 1973 that the stereochemistry-bioactivity relationships among pheromones would be elucidated only after successful synthesis of both the pure enantiomers of pheromones. If a synthetic... 

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

The relationships between stereochemistry and bioactivity among pheromones are diverse and far from straightforward. Organisms utilize chirality to enrich and diversify their communication systems.8,9 It must be emphasized that such diversity could be found only through experiments by using pure pheromone enantiomers of synthetic origin. In this section, several examples will be given to illustrate the diverse stereochemistry-bioactivity relationships. 

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]. 

Another important problem in 1973 when I started my pheromone synthesis was the relationship between the absolute configuration of a pheromone and its bioactivity. At that time there was no experimental result about the relationship, just because no one synthesized both the pure enantiomers of a pheromone. I really wanted to know the relationship, because among other bioactive compounds, there were several known cases, as shown in Figure 4.2. Only a single enantiomer of glutamic acid and also that of estrone are bioactive, while both the enantiomers of carvone as well as those of camphor were odoriferous. 

Because synthetic ( )-87 was pheromonally inactive, Tumlinson et al. carefully studied in 1977 the relationship between the enantiomeric purity of 87 and its pheromone activity.60 They synthesized the enantiomers of 87, starting from the enantiomers of glutamic acid. The bioactive enantiomer is (/ )-(—)-87, and (5 )-(+)-87 severely inhibits the action of (R)-87. Accordingly, (R)-87 of 99% ee is only two-thirds as active as pure (R)-S7 that of 90% ee is one-third as active, that of 80% ee is one-fifth as active as pure (R)-87. Both (7v )-87 of 60% ee and ( )-87 were inactive. These results illustrate convincingly the importance of enantiomeric composition in chemical communication. Later in 1996, Leal found that the sex pheromone of the female scarab beetle (Anomala osakana) is (S )-87, while (R)-87 interrupts the attraction caused by (.S )-87,61 Thus, chirality accounts for species discrimination. 

Extensive joint works by biologists and chemists revealed that diversity is the keyword of pheromone response. I never dreamed of such diversity when I began my pheromone research. At present, this kind of diversity can be clarified only through experiments. It is therefore a prerequisite to study the relationship between stereochemistry (including cis/trans-isomerism) and bioactivity, if we want to use a pheromone practically. 

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