Significance of chirality in pheromone science

This is the most common relationship, and the majority (about 60%) of the chiral pheromones belong to this category. (lR,5S,7R)- xo-Brevicomin (76), the aggregation pheromone of the western pine beetle, and (35,4/ )-faranal (95), the trail pheromone of the Pharaoh s ant, are the typical members of this group. 

Response of the gypsy moth to the enantiomers of disparlure (85) showed that (7R,8S)-85 was bioactive, while (7S,8R)-85 was inhibitory. The very strong inhibitory action of the opposite (5 )-isomer of japonilure (R)-87 is remarkable. In practical application of these pheromones, their pure enantiomers have to be manufactured. 

I explained this category in the case of the German cockroach pheromone (104), and also discussed the spined citrus bug pheromone [(3/ ,4S)-74], whose opposite enantiomer was as active as the pheromone itself. Females of the maritime pine scale Matsucoccusfeytaudi) use (3.S ,7R)-118 as the sex pheromone. Its OR,1R )-isomcr also showed bioactivity similar to the natural pheromone, while M. feytaudi males responded very weakly to the two other stereoisomers. It therefore seems that only the stereochemistry at C-7 of 118 is important for the expression of pheromone activity.139 

Females of the Douglas-fir beetle (Dendroctonuspseudotsugae) produce an average of a 55 45 mixture of (R)- and (5 )-119. The combined effect of the enantiomers was additive rather than synergistic, and both enantiomers are required for maximum response.140 

The azuki bean beetle (Callosobruchus chinensis) uses callosobruchusic acid (120) as the pheromone. Although (R)-120 is the major component of the natural pheromone (R/S = 3.3—3.4 1), (7 )-120 is only a half as active as (5 )-120.141 142 

---

Mori, K. (2007). The significance of chirality in pheromone science. Biorg. Med. Chem., 15, 7505-7523. 

The author s overview in Volume 8 of CONAP (first edition) briefly treated the relationship between stereochemistry and pheromone activity among insects.1 The significance of chirality in pheromone science was also discussed in depth by the author in 2007.8 Further examples were reported to show the importance of chirality in chemical communications among microorganisms9,10 and mammals.11 The microbial cases will be summarized in this section. 

---