O

a hexaketide

2,8-dimethyM ,7-dioxo-spiro[5,5]undecane

2,8-dimethyM ,7-dioxo-spiro[5,5]undecane

Figure 4.16 Two examples of cyclic ketal pheromones and the possible routes to their formation. Note that for the last compound, a dimethylspiroundecane, a number of isomers are possible traps for this forest pest. It has been pointed out by Francke that many C9 compounds like chalcogran could be derived by splitting unsaturated C18 acids. There are many C9 compounds used as pheromones. In this case a derivation from linolenic acid can be suggested (Figure 4.17). Note that the (2S,5i?)-form is active while the (25',55)-form is not, but the presence of the (2S,5S)-form does not affect the activity of the active enantiomer.

chalcogran

Figure 4.17 Suggested origin of the pheromone chalcogran from linolenic acid chalcogran

Figure 4.17 Suggested origin of the pheromone chalcogran from linolenic acid

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