Aromatic Pheromones

In contrast to the rutelines, the melolonthine scarabs generally use terpenoid-and amino acid-derived pheromones (reviewed in Leal, 1999). For example, the female large black chafer, Holotrichia parallela Motschulsky, produces methyl (2.S, 3. Sj - 2 - am ino-3-methy lpcn tanoatc (L-isoleucine methyl ester) as an amino acid-derived sex pheromone (Leal et al., 1992 Leal, 1997). There is no direct evidence that the chafer beetles or any other Coleoptera use the shikimic acid pathway for de novo pheromone biosynthesis, but some scarabs and scolytids (see section 6.6.4.2) may convert amino acids such as tyrosine, phenylalanine, or tryptophan to aromatic pheromone components (Leal, 1997,1999). In another melolonthine species, the female grass grab beetle, Costelytra zealandica (White), the phenol sex pheromone is produced by symbiotic bacteria (Henzell and Lowe, 1970 Hoyt et al. 1971). 

Figure 10 summarizes some results of the lipid-oxidation system in basldlomycetes, leaves, fruits, vegetables, and cereals. It can be seen that there is a development with evolution and differentiation. The enzyme system is highly substrate specific to a (Z,Z)-1,4-pentadiene system converting linoleic- and linolenic acids into carbonyls and oxoacids which may undergo further isomerization (E3) and/or reduction (E4). Some of the components formed are very potent aromatics, pheromones, and wound hormones. Basidio-mycetes and Fungi produce (-)-1-octen-3-ol as their sensorial principle. 9-Oxodecanoic acid is known as queen substance and is the sex pheromone of honey bees. 

When allylic compounds are treated with Pd(0) catalyst in the absence of any nucleophile, 1,4-elimination is a sole reaction path, as shown by 492, and conjugated dienes are formed as a mixture of E and Z isomers[329]. From terminal allylic compounds, terminal conjugated dienes are formed. The reaction has been applied to the syntheses of a pheromone, 12-acetoxy-1,3-dode-cadiene (493)[330], ambergris fragrance[331], and aklavinone[332]. Selective elimination of the acetate of the cyanohydrin 494 derived from 2-nonenal is a key reaction for the formation of the 1,3-diene unit in pellitorine (495)[333], Facile aromatization occurs by bis-elimination of the l,4-diacetoxy-2-cyclohex-ene 496[334],... 

Some male arctiid moths produce their courtship pheromone from dietary pyrrolizidine alkaloids acquired during feeding by the larvae [ 126]. Conversion of monocrotaline to hydroxydanaidal by males is accomplished by aromatiza-tion, ester hydrolysis and oxidation of an alcohol to the aldehyde [7]. In the case of Utetheisa ornatirx the stereo-configuration at C7 of the dietary alkaloid is the same as the pheromone released (R). In contrast, another arctiid, Creatono-tos transiens, can convert a dietary precursor alkaloid with the (S) configuration at C7 (heliotrine) to (l )-hydroxydanaidal. The biosynthesis occurs by first oxidation-reduction at C7 to convert the stereochemistry and then proceeds through aromatization, hydrolysis, and oxidation [7]. 

The repertoire of chemicals that can be used for communication is limited by the biosynthetic ability of the insect. Compared to other insect orders, pheromone biosynthesis in Hymenoptera has received little study [191]. However, the biosynthetic origins of chemically diverse hymenopteran semiochemicals likely include aromatic, fatty acid, and terpenoid pathways as well as simple modifications of host-derived precursors. Notable recent studies include the biosynthesis of the fatty acid components (2 )-9-oxodec-2-enoic acid 52 and (2 )-9-hydroxydec-2-enoic acid of the honeybee queen mandibular pheromone from octadecanoic acid [192,193], and the aliphatic alcohol and ester... 

Pheromone chemistry in scarab beetles, chafers, and dung beetles covers a wide range of structures, including esters of amino acids and aromatics as well as branched and straight chain aliphatic compounds, among which a row of y-lactones forms a most characteristic group. 

Insects communicate through the use of a great variety of volatile pheromones. As mentioned in Chapter 8, Section A,l, some moths utilize acetate esters of various isomers of A7 and A11 unsaturated C14 fatty acids as sex pheromones. Some other moths convert the trans-l 1 -tetradecenyl acetate into the corresponding C14 aldehyde or alcohol, while others use similar compounds of shorter (Cn - C12) chain length.143 Some ants use ketones, such as 4-methyl-3-heptanone, as well as various isoprenoid compounds and pyrazines as volatile signaling compounds.144 Other insects also utilize isoprenoids,145 alkaloids,146 and aromatic substances as pheromones. 

Analytical Properties Separation of positional isomers of aromatic compounds and geometrical isomers of sex pheromones Reference 7... 

Male moths and butterflies have proven to be an especially rich source of interesting natural products. The sex pheromone produced in the wing glands of the lesser waxmoth, Achroia grisella, is composed of n-undecanal and (Zj-ll-octadecenal (98), whereas that of the greater waxmoth also contains n-undecanal (.99) but is dominated by n-nonanal (100). The scent brushes of male noctuid moths produce large amounts of aromatic compounds and terpenes which are believed to function as aphrodisiacs (101). Benzaldehyde, 2-phenyl ethanol, benzyl alcohol, 6-methyl-5-hepten-2-one, pinocarvone, and isobutyric acid have been identified in the secretions of different noctuid species (102), and it appears that these pheromones may possess some chemotaxonomic value. 

In addition to acyclic ketones, dolichoderine ants in the genus Azteca generate an alarm signal with 2-methylcyclopentanone (xxxi),cis-l-acetyl-2-methylcyclopentane (XXXII), and 2-acetyl-3-methylcyclopentene (XXXIII) (128). That some ant species utilize aromatic compounds as alarm pheromones is demonstrated by the identification of methyl 6-methyl salicylate (XXXIV) in the... 

An asymmetric reducing agent (49), prepared from LAH, (-)-)V-methylephedrine (14) and 3,5-di-methylphenol in a 1 1 2 ratio, reduces acetophenone with 83.8% A series of aromatic and alkynyl ketones are reduced by (49) to the corresponding (f )-alcohols (Scheme 1)P Some of the products are useful intermediates for the synthesis of 7-lactone insect pheromones. " ... 

As shown in Fig. (12), conversion of plant PAs into the pheromone has been suggested to occur in U. ornatrix through aromatization of the dihydropyrrole ring of monocrotaline, followed by ester hydrolysis and... 

Acylpyrazines, constituents in foodstuffs and pheromones, have been prepared by the Minisci-type radical reactions of pyrazines even though these methods often suffer from poor regioselectivity of aromatic substitution. Alternatively, synthesis of acetylpyrazines and propionylpyrazines 33 was achieved via a Stille coupling of bromopyrazines 31 with tributyl-(l-ethoxyalkenyl)tin (32), followed by acidic hydrolysis of the ether derivative [24]. 

In this work, we showed the usefulness of cm-selective hydrogenation of aromatic rings in pheromone synthesis, and also illustrated the usefulness of GC comparison in stereochemical investigation. 

---