Aromatic Pheromones

A number of compounds easily recognized as derivatives of the phenyl-C3 series have been identified as pheromones (Figure 8.2). For example, ethyl cinnamate has been found as a component of the male sex phero-mone of the oriental fruit fly Grapholitha molesta. 2-Phenylethanol has been found in the mandibular glands of the ant Camponotus clarithorax, o

/ — x „ v, . pyridoxal /=\ 0 o in mammals /=\ V „,<

,0 s0h phenylpyruvic acid

NHp phenylalanine nh;

,0 'oh tyrosine phenylpyruvic acid

NHp phenylalanine nh;

tyrosine

ch30

H0A\

ch2-oh coniferyl alcohol lignin

Figure 8.2 Some simple phenyl- C3 derivatives from phenylpyruvic acid, including some insect pheromones. The formation of 1-phenylethanol has not been investigated. Benzaldehyde can be formed in more than one way. Coniferyl alcohol, an attractant for a fruit fly is the precursor of the important plant product lignin

-ch2

nh2 phenylalanine

Figure 8.3 The oxidation of phenylalanine with the NIH shift and without it. The dot on hydrogen represents a label tyrosine h+ + h0-{ />— ch2-t~ct nh2 oh h

Figure 8.3 The oxidation of phenylalanine with the NIH shift and without it. The dot on hydrogen represents a label and provides the male sex pheromone of the lepidopteran bertha army-worm Mamestra configurata. In the latter case labelling showed that the 2-phenylethanol was derived from phenylalanine, and the route probably went via cinnamic acid, since the pheromone was also produced from [3-14C]cinnamic acid. It was suggested that phenyllactic acid was also an intermediate and the final precursor was the glucoside of phenylethanol. CKJ-l-Phenylethanol is the trail pheromone of the ant Aphaenogaster cockerelli. Benzaldehyde has been found widely in Coleoptera and in some Hymenoptera, and is often associated with HCN in millipedes and some insects as a defensive secretion (Chapter 10). Benzoic acid (in Coleoptera) and phenylacetic acid (in ants) are also widely found, as well as a number of simple esters of phenylacetic acid. Coniferyl alcohol is an attractant for females of the oriental fruit fly, but its immediate precursors are obtained from flowers (Chapter 10).

Adult males of a number of Lepidoptera use simple phenyl-Cb and - C2 compounds like benzyl alcohol, benzaldehyde, /?-hydroxybenzaldehyde, phenylacetaldehyde and 2-phenylethyl acetate as copulating pheromones. Adult males of leaf-footed bugs {Leptoglossus species) use a variety of simple aromatic compounds in abdominal glands, apparently for species recognition. Among these are guaiacol, vanillin, cinnamyl alcohol and syringaldehyde (Figure 8.4). Their origin has not been studied. The curious example of 2-nitroethenylbenzene (2-nitrostyrene) (Figure 8.4) has been found in the defensive secretion of the millipede Eucondylodesmus elegans, and shown to be repellant to ants. When [2H8]phenylalanine was fed to the millipedes, [2H7]-2-nitroethenylbenzene was detected by mass spectrometry.

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