Pheromones, unsaturated

By the radical pathway l, -diesters, -diketones, -dienes or -dihalides, chiral intermediates for synthesis, pheromones and unusual hydrocarbons or fatty acids are accessible in one to few steps. The addition of the intermediate radicals to double bonds affords additive dimers, whereby four units can be coupled in one step. By way of intramolecular addition unsaturated carboxyhc acids can be converted into five raembered hetero- or carbocyclic compounds. These radical reactions are attractive for synthesis because they can tolerate polar functional groups without protection. 

Fig. 2 Action of desaturases and limited chain shortening can produce a variety of mono-unsaturated acyl-CoA precursors that can be modified to form unsaturated pheromone compounds. The arrow pointing down indicates limited chain shortening by two carbons. Modification of all 16-, 14-, 12-, and 10-carbon acyl-CoA derivatives on the carbonyl carbon can account for the majority of monounsaturated acetate esters, aldehydes, and alcohols identified as sex pheromones...

The unsaturated lactone in (4.71) adds to ethylene to give a precursor of the pheromone ( )-grandisol (4.71)483). 

In contrast to pheromones that involve single complex compounds, many moth species have been found to utilize a specific blend of relatively simple fatty acid-derived compounds. It appears that the evolution of a unique enzyme, A1 desaturase, used in combination with 2-carbon chain-shortening reactions (Figure 3) has allowed moth species to produce a variety of unsaturated acetates, aldehydes, and alcohols that can be combined in almost unlimited blends to impart species specificity. For example, biosynthetic precursors for the six-component pheromone blend of acetates for the cabbage looper moth (12) (Figure 2) can be determined easily from the cascade of acyl intermediates produced by the A11-desaturase and chain-shortening reactions (Figure 3). 

While these functionalized ethers maybe long range signals,long chain unsaturated ketones, isolated from the elytra of females of the related species Anoplophora malasiaca, act as contact pheromones. The mixture of 10-hepta-cosanone, (Z)-18-heptacosen-10-one, (18Z,21Z) -18,21 -heptacosadien-10-one and (18Z,21Z,24Z)-18,21,24-heptacosatrien-10-one 188 proved to show pronounced biological activity [349]. 

Females of the cowpea weevil, Callosobruchus maculatus, release a male attracting pheromone from the tip of their abdomen. The volatile signal contains five unsaturated, branched C8-acids 208-212 [376,377]. Individual compounds proved to be active while mixtures showed additive effects. Similarly, compounds 208 and 209 have been identified as the female produced sex pheromone of C. subinnotatus [378], while 209 had been described as the sex pheromone of C. analis [379]. However, GC-MS analyses of female produced volatiles of C. analis failed to detect any of the C. maculatus compounds, but did find an unidentified C8-acid with a retention time different from any of the C. maculatus acids [377]. 

A very simple synthesis of the pheromone exo-brevicomin (4i) proceeds via an electrochemical Kolbe condensation between the unsaturated carboxylic acid 39 and the ketoacid 40, followed by hydroxylation of the double bond with OSO4, as... 

This long-chain unsaturated ester serves as one component of a mnlticomponent female sex pheromone for 140 species of moths as well as the Asian elephant. This is nnlikely to cause any real confnsion in nature. On the one hand, the 140 species of moths keep ont of each other s way and out of the elephant s way by varying the nature and relative concentrations of other components in the multicomponent pheromone. On the other hand, the male elephant is not likely to detect the extremely small amonnts of this pheromone released by female moths. Chemistry aside, there are other obvions difficnlties in moths mating with elephants in the wild. 

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