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a-farnesene

P-farnesene nerolidol

Figure 6.17 The formation offarnesyl pyrophosphate by addition of another molecule of isopentenylpyrophophate (IPP) to geranylpyrophosphate, and some simple sesquiterpenes a-farnesene

P-farnesene nerolidol

Figure 6.17 The formation offarnesyl pyrophosphate by addition of another molecule of isopentenylpyrophophate (IPP) to geranylpyrophosphate, and some simple sesquiterpenes geranyl pyrophosphate, gives farnesyl pyrophosphate, the parent of the sesquiterpenes (Figure 6.17). Hydrolysis, or rearrangement followed by hydrolysis, or dehydration leads to a number of products as for the monot-erpenes. By suitable folding, further cyclic products are obtained. Some monocyclic sesquiterpenes are shown in Figure 6.18. There are many bicyclic (and more complex) sesquiterpenes in plants. Juvabione comes from some species of fir tree, particularly the American Abies balsamea. It was accidentally discovered to be a mimic of insect juvenile hormone (see below) but it only affects the growth of a small number of insects.

Dendrolasin, a defensive compound from the mandibular glands of an ant, may be seen as an oxidation product of p-farnesene. Labelled sodium acetate, sodium mevalonate and glucose were all incorporated into dendrolasin by the ant, but the label was scattered over all the carbon atoms, so that firm conclusions about the biosynthetic route could not be made.

The aggregation pheromone of the rusty grain beetle Cryptolestes ferrugineus is a mixture of large ring lactones called cucujolides l OH"

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