Isomere, pheromone, separation

Product stereochemistry is a critical factor determining the applicability of metathesis pheromones to insect control [23]. The steric course of the metathesis reaction normally results in a (thermodynamic) cis/trans mixture, whereas the physiologically active pheromones are either isomerically pure compounds or specific cis/trans mixtures. When it is necessary to obtain a single stereoisomer, the separation step required is tedious and expensive. The synthesis of pure cis isomers via the metathesis reaction, therefore, forms a challenge for catalyst development. 

G. c. conditions have been established for the separation of 24R- and 245-isomers of 24-methyl-steranes and -stanol acetates, and are applied to the analysis of steranes in a sedimentary rock and in petroleum.Isomeric 24-ethyl-steranes were sufficiently separated under the same conditions to allow a rough analysis of 24i -245 mixtures. Liquid crystalline cholesteryl cinnamate has proved effective as a stationary phase for the capillary-g.c. separation of insect pheromones e.g. tetradecen-l-yl acetates differing in the position of unsaturation). 

Bark beetles of the genus Ips are pests which attack pine and spruce trees. They use ipsdienols as aggregation pheromones, Ips confusus emitting the (5)-(-l-)-, and Ips paraconfusus the (.K)-(-)-enantiomer The beetles receive the myrcenes (section 2.2) occurring in conifers with their food and metabolize them to ipsdienols some evidence for de-novo synthesis by the bugs is also reported. In order to catch the beetles, pheromone traps are supplied with both enantiomers of ipsdienol which are produced from (-l-)-verbenone, a constituent of the Spanish verbena oil (section 2.4.3). This terpenone, also available by oxidation of a-pinene, is isomerized to the enantiomers of 2(10)-pinen-4-one via three steps (reduction, protonation, oxidation). After separation, both enantiomers are reduced by lithiumaluminumhydride. Pyrolytic cycloreversion of the resulting diastereomeric 2(10)-pinen-4-ols provides the enantiomers of ipsdienol... 

Mixtures of pheromones can often be complex and demanding to separate, particularly when isomers of molecules are present. This is particularly acute in the study of social insect cuticular hydrocarbons and which are often complex mixtures of 50 or more different hydrocarbons of increasing chain length (Figure 8). For these mixtures the separation of isomeric hydrocarbons such as 9-, 11-, and 13-methyl-heptacosane is not possible, which has a consequent impact on peak integrations and statistical correlation of these data with colony function. 

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