Pheromones structural diversity

Contrary to the structure similarity of the pheromones secreted by taxonomical related moths, some differences are necessary for their sexual communication systems to play an important role in their reproductive isolation. In addition to further modifications of the various structures, diversity of the lepidopteran sex pheromones is generated by blending multiple components. Innumerable pheromone blends are based not only on combinations of different components but also on variations in the mixing ratio. A pioneer study with Adoxophyes spp. (Tortricidae Tortricinae) had already proposed this concept in the early 1970s. While the smaller tea tortrix (A. honmai) and the Japanese summerfruit tortrix (A. oranafasciata) had been considered to be variant strains with different host preferences in the same species, Tamaki et al. found that females of the former pest insect in the tea garden secreted Z9-14 OAc and Zll-14 OAc in a ratio of 7 4 but females of the latter defoliator of apple trees secreted them in a ratio of 13 4 [127,128]. Furthermore, two other components (Ell-14 OAc and MelO-12 OAc) were subsequently identified from the former species [129]. 

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. 

There have been a couple of recent and excellent reviews of the ultrastructure of exocrine cells in general (Quennedey, 1998) and pheromone-secreting cells in social insects in particular (Billen and Morgan, 1998). This chapter attempts to survey the structural diversity of cells that produce sex pheromone in insects, particularly from a phylogenetic perspective, in part based on advances made... 

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). 

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)... 

The male D. crlstata respond to 8-methyl-2-decanol acetate. However, when the four isomers of the acetate were tested, D. crlstata males responded only to the (2S,8R)-isomer (39). Thus both structural diversity and stereoisomerism are being used by this group of insects to achieve specificity in their chemical signals. NO evidence of multicomponent pheromones in this group has yet been discovered. 

This group of natural compounds is also structurally diverse ranging from the simple dienes like a sex pheromone (4E,7Z)-4,7-tridecadienyl acetate or ( )- , )-coriolic acid through typical polyenes like the all-trans-stereomer of ethyl retinoate to the more complex, optically active calyculins A and B. In the total syntheses of polyenes presented below, the structurally complex phosphonate or bisphosphonate reagents were used in the Horner-Wittig olefination reactions solely or in combination with the Suzuki coupling. 

The polycycles, synthesized with the use of phosphonates and discussed below, represent a group of structurally diverse compounds that exhibit a wide spectrum of biological activity. They are antibacterial or spasmolytic agents, pheromones and ingredients of fragrance oils. In this Section syntheses of... 

The chiral pool approach for the synthesis of enantiomerically pure compounds uses readily available sources of enantiomerically pure starting materials, usually naturally obtained. The most common sources are amino acids, monosaccharides and terpenes. Using this approach a number of structurally diverse enantiomerically pure compounds have been synthesised by carrying out a series of chemical transformations which will preserve the chiral information. There are both simple and more complex examples of this approach. For example, the insect pheromone (/ )-sulcatol (3) and the more complex fragment of brevetoxin B (2) are both prepared from 2-deoxy-D-ribose (Scheme 4.1) [2, 3]. 

Thus, starting from ethyl (5)-p-hydroxybut5rrate, pheromones of diverse structural types, such as (5)-sulcatol [26], femilactone II [27], (25,6i )-2-methyl-l,7-dioxaspiro[5.6]-dodecane [28], (25,6/ ,S5)-2,8-dimethyl-l,7-dioxaspiro[5.5]undecane [29], (2R,5S)-2-methyl-5-hexanolide [31], and (2S,SjR)-8-methyl-2-decanol propanoate [32], have been synthesized. Methyl (5)-P-hydroxybutyrate has also been used for the synthesis of (25,35,75)-3,7-dimethylpentadecan-2-ol [33]. In these syntheses, the configurations at the... 

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