Ant pheromones

Probably the best-studied communication behavior in ants is chemical communication, but other sensory modalities, such as mechanical cues, also play an important role in the formation of multicomponent signals in ant communication. Chemical releasers are produced in a variety of exocrine glands, and considerable progress has been made in chemically identifying many of these glandular secretions (for reviews see refs. 1 and 2). In this essay I will not emphasize, however, the natural product chemistry of ant pheromones, but rather concentrate on the proposition that communication in ant societies is often based on multicomponent signals, on nested levels of variation in chemical and other cues, which feature both anonymous and specific characteristics (3). 

The highly organized, emergent social behavior of ants reflects the action of a number of ant pheromones. 

The blind snake Leptotyphlops dulcis is a specialized burrower that feeds on termites and ant brood. It follows the ant pheromone trails to find its prey (Section 12.1). when attacked by ants, this snake tilts its scales individually so that the skin appears silvery. While it writhes, it covers itself with feces and a clear viscous fluid, discharged from the anus. It may also assume a stationary coiled position. when it resumes searching and feeding, it is no longer attacked by ants. The effect lasts from 3 to 30 minutes (Gehlbach etal., 1968). Here a predatory species protects itself from the defensive actions of its prey. 

T )-2,4-dimethyl-2-hexenoic acid, a male ant pheromone in the genus Camponotus ... 

Trifluorinated analogues of monomorin, an indolizidin-type alkaloid that is an ant pheromone,and of vincamine derivatives have been described (Figure 4.54). ... 

Minisci-type substitution is one of the most useful reactions for the synthesis of alkyl- and acyl-substituted heteroaromatics. The acyl radicals are formed by the redox decomposition from aldehyde and /-butyl hydroperoxide or by silver-catalyzed decarboxylation of a a-keto acid with persulfate. Synthesis of acylpyrazines 70 as ant pheromones are achieved by this methodology using trialkyl-substituted pyrazines 69 with the acyl radicals generated from aldehydes or a-keto acids (Equation 10) <1996J(P1)2345>. The latter radicals are highly effective for the acylation. Homolytic alkylation of 6-chloro-2-cyanopyrazine 71 is performed by silver-catalyzed decarboxylation of alkanoic acids to provide 5-alkyl-substituted pyrazines 72 (Scheme 18) <1996CCC1109>. 

A dramatic example is the synthesis of the ant pheromone monomorine 48 already discussed in chapter 8. A bold double C-N disconnection gives the amino-diketone 49 and hence, after FGI of NH2 to NO2, the 1,4-disconnection we have just described. 

Except where indicated, taken from pheromone compendia (a) M. S. Mayer and J. R. McLaughlin. Handbook of Insect Pheromones and Sex Attractants. 1991 CRC Press, Boca Raton, Florida, (b) (Mori, 1998) (c) J. Hardie and A. K. Minks (eds.). Pheromones of Non-Lepidopteran Insects Associated with Agricultural Plants. 1999 CABI Publishing, Wallingford, UK. The major component is listed first. % = Other less abundant pheromone component(s) (u) = further pheromone component(s) remain unidentified. For newly identified honeybee pheromone components, see Keeling et at. (2003), for new ant pheromone components see Baird (2001). 

Despite their critical importance in mediating insect behaviors, we still know very little about the detailed roles and mechanisms of insect cuticular lipids as signal molecules, in part because it is not immediately obvious how such signals could be manipulated and exploited for insect management, as is done with the more well-known volatile sex attract-ant pheromones. Even for the comparatively few species that have been examined in any detail, there are large gaps in our knowledge, for several reasons. 

A synthesis of the enantiomerically pure ant pheromone is required. One suitable starting material might be the enantiomerically pure alkyl bromide shown. Suggest a synthesis of the pheromone based on this or another starting material. 

Wistrand [203] described the highly diastereoselective synthesis of an enantiopure ant pheromone starting from L-proline using an organocopper nucleophile in the presence of borontrifluoride for the amidoalkylation reaction as shown in Eq. (40). 

A synthesis of this enantiomerically pure ant pheromone was required for the purposes of pest control. Given a supply of the enantiomerically pure alkyl bromide as a starting material, suggesta synthesis of the pheromone. 

Enders has used these asymmetric Michael additions as the key steps in the enantioselective synthesis of various esters and alcohols (69-73) which are chiral volatile ant pheromones. In these syntheses, asymmetric Michael additions of the lithio salt of the SAMP hydrazone of propanal to methyl 2-but-enoate and methyl 2-pentenoate were used to establish the chiral centers. Subsequent hydrolysis and reduction of the aldehyde or carboxylic acid ester by conventional procedures afforded the pheromones. ... 

Figure 6.7. Natural products using the [2,3]-Wittig rearrangement as the key step (a) ant pheromone [58] (b) t aromycin A (J768) (c) Prelog-Djerassi lactone (J771) (d) aristolactone...

The regioselective reaction of HC02Et or CO(OEt>2 with an unsymmetrica ketone is important as it activates that side of the ketone towards enolisation (Chapters 14 and 20). Thus ketone (89) gives (90) and not (88) on condensation with CO(OEt)2 as only (90) can form a stable enolate ion (91). The product was needed for a synthesis of the ant pheromone (92) (see Chapter 29). 

This reaction was adapted to the synthesis of the pharaoh ant pheromone monomorine. 

Figure 4.8 Illustrating the formation of 3-ketones, typical of ant pheromones. The polyketide shown in square brackets does not have any real existence...

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