Pheromones structure

Coleoptera comprise the largest order of insects and accordingly pheromone structures and biochemical pathways are diverse [98, 99]. Beetle pheromone biosynthesis involves fatty acid, amino acid, or isoprenoid types of pathways. In some cases dietary host compounds can be converted to pheromones, but it is becoming apparent that most beetle pheromones are synthesized de novo. 

FIGURE 2 Pheromone structures of the American cockroach (periplanone B), the brownbanded cockroach (supellapyrone), bark beetles (ipsdienol enantiomers), and the cabbage looper moth (six acetates). 

Third, some of the pheromone components are simple and cheap compounds such as straight-chain esters and aldehydes, that are readily available in bulk. Others fall into a middle ground, whereby multigram-scale synthesis to produce sufficient material for use as trap lures should be possible. However, the pheromone structures of a number of species appear to be of sufficient complexity that it is unlikely that they could be made in sufficient quantity and at affordable cost for widespread use in pheromone-based control programs. 

Attractive Compounds. Though the first report on the identification of a pheromone from a scarabaeid beetle dates back more than 30 years - phenol as an attractant for males of the gras grub beetle Costelytra zealandica [135] which turned out to be produced by beetle associated bacteria [136] - most of the pheromone structures known today have been elucidated during the last decade [3,137,138]. 

Figure 1 Peptide pheromone structures determined by NMR. (a) Structure of peptide pheromone (PinA) from Lactobacillus plantarum required for piantaricin biosynthesis. (b) Structure of peptide pheromone (ComC) from Streptococcus pneumonia required for competence deveiopment. ...

As discussed below, l,3,7-trimethyl-(Z)-2,6-octadienyl formate and 1,3,7-trimethyl-(Z)-2-octenyl formate, prepared as mimics of the aggregation pheromone structure, had alarm pheromone-like activity, whereas 1,3,7-trimethyloctyl formate and simplified 1-methylalkyl formates showed aggregation pheromone-like activity with C. lactis, whose alarm pheromone is neral (2) (Honma et al, 1995). The evidence suggests that for those species which use neral (2), geranial (6), or neryl formate (1) as alarm pheromones, the presence of (Z)- or ( )-allylic double bonds in the molecules are essential for biological activity. 

The behavior of the males was used in a bioassay-guided identification of the pheromone, which was extractable by polar solvents such as water or methanol. The bioassay apparatus consisted of a cardboard channel with silk samples treated with different extracts. A positive response consisted of a male producing a typical drumming behavior upon contact with a stimulus. Because males responded to some extent to silk without pheromone, individual spiders were tested first with inactive silk, followed by extract-treated silk (Tichy et al, 2001). GC-MS analyses of the active silk extracts were not successful, even using several derivatization procedures. However, the pheromone structure was deduced by NMR spectroscopy... 

Many studies have provided evidence that pheromones on the silk and/or the cuticle of females stimulate courtship or related behaviors in males, as do the few pheromones that have been fully identified to date. Contact with the pheromone and with silk or cuticle is usually necessary to evoke the proper courtship responses. Olfactory cues, such as those in A. aperta, may release courtship when the male is in contact with silk. There are insufficient data to draw conclusions about which classes and types of chemical might typically be used for the various kinds of pheromone, particularly as the few identified pheromone structures vary widely in polarity, volatility, and other chemical characteristics. 

The goal of this chapter is to provide an overview of the occurrence of Type II polyene pheromones and their derivatives, and their chemistry, including their biosynthesis and synthesis. The older literature in this subject area was reviewed in Millar (2000), and summarized more recently in Ando et al. (2004). Thus, this chapter will provide a comprehensive summary of all known Type II pheromone structures and their occurrence in Tables 1 1, whereas the text will focus more on work over the past ten years. The interested reader is further directed to three useful online databases, two of which focus on lepidopteran pheromones (www.tuat.ac.jp/ antetsu/review/e-List.pdf Ando, 2003 www-pherolist.slu. se/pherolist.php Witzgall et al., 2004) and the third of which covers insect pheromones in general (www.pherobase.com El-Sayed, 2008). 

Scheme 1. Examples of Type II lepidopteran pheromone structures...

Within the Lymantriidae, patterns of pheromone use are not yet clear, and there appears to be the greatest diversity of pheromone structures. Roughly two-thirds of the approximately thirty species for which pheromones or sex attractants have been reported have polyenes, epoxides, ketones, or polyunsaturated esters that could be classified as belonging to the Type n class, whereas the remainder use branched-chain epoxyalkane pheromones. Remarkably, even within a genus (e.g., Lymantria or Euproctis), congeners produce pheromones of different classes (Table 18.4). 

Lesser tea tortrix. A minor component of the sex pheromone blend of this moth is 10-methyl-l-dodecanol acetate, V, (Figure 10) (48). Mori has synthesized the enantiomers both compounds were constructed from (R)-(+)-citronellol (49). The racemic target compound was synthesized by alkylating 10-undecenoic acid (as its dianion) with ethyl iodide (50). Reduction of the carboxyl to a methyl group was accomplished by standard procedures. Hydroboration of the olefinic link with disiamylborane and oxidative workup yielded the primary alcohol which was then acetylated to give the racemic pheromone structure. The overall yield from undecenoic acid was 40-45% without any extensive effort to optimize. 

A unique pheromone structure is represented by the alkaloid l,3-dimethyl-2,4-(17/,3 /)-quinazolinedione (Ar56), which is the sex pheromone of the pale-brown chafer Phyllopertha diversa260 Its degradation with special enzymes on the antennae leading to signal inactivation has been described 261... 

Pheromones of insect species in the order Coleoptera are characterized by considerable structural diversity. Unlike the lepidopterous sex pheromones, which are nearly all tatty acid derivatives, coleopterous sex pheromone structures range in complexity from the relatively simple 3,5-tetradecadienoic acid of the black carpet beetle to the tricyclic terpenoid, lineatin, of the striped ambrosia beetle. While the sex pheromones of many beetles consist of mixtures of compounds that act synergistically to elicit a behavioral response, other Coleoptera species appear to use only a single compound for chemical communication between the sexes. In the latter case the compound usually has at least one chiral center and chirality plays a major role in determining pheromone specificity. 

Bark beetles are of great economic importance, which is one of the reasons more research has been done on the pheromones of the Scolytidae than on those of any other family of Coleoptera. Their pheromone systems also seem to be typical of the Coleoptera in that while there is considerable diversity in pheromone structure within this family, there also seems to be a pattern of structures, particularly within a genus. The first pheromone identified from a coleopterous species was from Ips paraconfusus Lanier (then I. confusus) by Silverstein et al. (13). Three compounds — ipsenol (I), ipsdienol (II), and cis-verbenol (III)... 

Although insect pheromone structures represent a myriad of chemical functionalities [6], the composite pheromones can be classified into six behaviourally functional groups sex, aggregation, dispersal (spacing or epideictic), alarm, recruitment (trail), and maturation. 

The sex pheromone structure, 10-methyl-2-tridecanone, was synthesized using the carboxyl group as the source of the methyl branch (lA) (Figure 6). Undecylenic acid was a-propylated and resolved via amides. The procedure followed allowed us to obtain the alcohols,(R)- and (S)-2-propyl-10-undecenol (>99.6% ee). The corresponding bromide was reduced with lithium triethylborohydride (15) then the double bond was converted to a methyl ketone by a) oxymercuration, b) reduction of the C-Hg bond with sodium borohy-dride, and c) oxidation with dichromate. The male southern corn rootworm responds only to the (R)-configuration no biological activity was noted for the (S)-enantiomer. Therefore, in this instance the racemic compound would be predicted to monitor this species adequately. 

Pheromones, structure, synthesis, biological activity of 82YGK1068, 82YZ899 81YGK63. 

Despite these advances, our knowledge about pheromone structure, production, and effects in marine invertebrates is scarce. A Boolean literature search from the past 20 years (1990-2009) showed that most pheromone studies with marine invertebrates have investigated crustaceans, polychaetes, and molluscs (Fig. 1.2). Especially during... 

Fig. 27.2 Pheromone structures of some groups of moth and beetle pests. The names of the chemical structures in the blend of boll weevil pheromone components (2e) are (Z)-2-(3,3, dimethyl)-cyclohexylideneethanol (grandlure II) and (Z)-(3,3-dimethyl)-cyclohexylideneacetalde-hyde (grandlure HI). The chemical name of S-rhynchophorol (2f) is 4S-( )-6-methyl-2-hepten-4-ol. From The Pherobase (http //www.pherobase.com)...

There are many more pheromone structures derived from fatty acids, but they all arise by chain extension or shortening, double bond introductions, oxidations and reductions as outlined in these examples. 

The nature of functional groups in a pheromone can be determined by chemical modification coupled with a sensitive bioassay of the converted material. For example, if a pheromone loses activity after saponification and regains it upon acetylation it likely contains an acetate group. Loss of activity after hydrogenation indicates unsaturation. Inscoe and Beroza (IS) tabulated many of the typical functional group tests that can be used in pheromone structure elucidation. These tests need not be restricted to purified material they can be employed on crude extracts as well and the results may suggest purification methods to be used (or avoided). 

Three examples of how some of the above methods have been successfully combined to elucidate pheromone structures are given below. 

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