Alcohols as pheromones

The fatty acid content of the ovipositor tips of a variety of Lepidopteran species were determined by acid methanolysis followed by gas-liquid chromatography (GLC) (4.). In each case, unusual fatty acids corresponding to pheromone components were identified. For example, the tufted apple bud moth, Platynota idaeusalis, uses (E)—11—tetradecenyl acetate and alcohol as pheromone components (5.) and also contains (E) -11—tetradecenoic acid in its ovipositor tip. In several species, the fatty acid content of the rest of the insect also was determined. In each instance, the unusual fatty acid components were found only in the ovipositor tip or in the pheromone-producing gland located in the tip. 

Acetalization of oxo aldehydes is used to protect sensitive aldehyde products, especially in asymmetric hydroformylation preventing racemization of an a-chiral aldehyde product [18-22,27]. Acetal formation can also be applied to the synthesis of monocyclic or spirocyclic pyranes as potential precursors and building blocks for natural products such as pheromones or antibiotics. A representative example is the synthesis of the pyranone subunit of the Prelog-Djerassi lactone. For this purpose, various 1,2-disubstituted homoal-lylic alcohols were used (Scheme 3) [32],... 

Three PAG-active compounds were identified from the extracts of pheromone glands of the persimmon fruit moth, Stathmopoda masinissa Meyrick (Lepidoptera Oecophoridae). These were AE,6Z)-4,6-hexadecadienal and the corresponding acetate (EA,Z6- 6 OAc) and alcohol EA,Z6- 6 OY ). A preliminary field trail confirmed that the acetate as a single component attracted male moths, the possible roles of the aldehydes and the alcohol as components of lures remains to be determined. 

The stoichiometric approach has been successfully used as the key step for the synthesis of biologically active compounds, to obtain enantioenriched allylic alcohols, as illustrated by the synthesis of conduritols derivatives 84 or the aggregation pheromone of the Douglas-fir beetle 85 , as well as enantioenriched oxiranes, intermediates for the synthesis of (—)-isomenthone 86 ° (Scheme 34). 

This transformation has been applied to several chiral production processes, the first being the synthesis of a pheromone (Disparlure) intermediate (S) albeit with low turnover numbers and only 91 % ee. Another industrial product is the epoxide of allyl alcohol as developed by PPG-Sipsy, to give a process where catalyst loading was decreased by molecular sieve addition and the safety factors involving peroxide contamination were overcome. These examples are shown in Figure 1.46. 

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. 

Fatty alcohols are found as components of waxes and, e.g., as pheromones in insects (cf. other lipids). 

The majority of the known cuticular lipid constituents that function in chemical communication processes are hydrocarbons (Howard and Blomquist, 1982 Blomquist and Dillwith, 1985 Howard, 1993 Nelson and Blomquist, 1995). Most oxygenated lipids that function as pheromones are not part of the surface lipids but are secretory products of specialized glands (Tamaki, 1985 Am et al, 1986 Morgan and Mandava, 1988). Many of the compounds in pheromones are short-chain unsaturated aldehydes, ketones and acetate esters of short-chain (C10-C14) unsaturated alcohols. Those short-chain lipids (biological activity have been reviewed elsewhere (Blomquist and Dillwith, 1985 Tamaki, 1985 Lockey, 1988 Blomquist et al., 1993 Jurenka and Roelofs, 1993 Howard, 1993). 

However, whereas the silkworm female appears to attract males with a single sex pheromone, many other insects use blends of pheromones as chemical releasers of behavior. This phenomenon is strikingly illustrated in the case of males of the bark beetle Ips paraconfusus (=Ips confusus) which utilize three monoterpene alcohols as an aggregation pheromone (11). Maximum attraction of beetles in the field was exhibited in the presence of a mixture of all three compounds, whereas single or pairs of compounds were considerably less active (12). Similarly, in laboratory bioassays, mixtures of compounds were vastly superior to single constituents as attractants (13). 

Another insect pheromone synthesis illustrates one of the drawbacks of chiral pool approaches. The ambrosia beetle aggregation pheromone is called sulcatol and is a simple secondary alcohol. This pheromone poses a rather unusual synthetic problem the beetles produce it as a 65 35 mixture of enantiomers so, in order to mimic the pheromone s effect, the chemist has to synthesize both enantiomers separately and mix them together in the right proportion. 

While two reactions, chain shortening and 11-desaturation, are key steps in the biosynthesis of many pheromones, these pathways also require a reductive step where the acid group is converted to an alcohol, acetate or aldehyde. Studies on the spruce budworm moth (12), Choristoneura fumiferana, and various Heliothis species (13.) indicate that there is a series of reactions, such as those in Fig. 3, to account for the various functionalities. Alcohols and acetates may be stored or released as pheromone aldehydes are too reactive (and potentially dangerous to the insect) to store and so are only produced immediately before release. 

More extensive studies have been done on the spruce budworm, Choristoneura fumiferana, (2JL) which uses (E) - and (Z) -11-tetradecenal as pheromone components. Once again, the first step appears to be reduction of the acid to an alcohol. Then an acetyl Co A fatty alcohol acetyltransferase converts the alcohol to the acetate ester (12.). The enzyme is specific for alcohols with chain lengths of 12-15 carbons, and prefers monounsaturated alcohols to saturated ones. It is located specifically in the pheromone gland, and appears to be microsomal. 

The redbanded leafroller moth uses a mixture of (E) and (Z) -11-tetradecenyl acetates as pheromone components. The pheromone gland of this insect also contains an acetyl Co A fatty alcohol acyl transferase (22.). This enzyme will acetylate 12, 14 and 16 carbon alcohols, and prefers the saturated alcohol to the Z monounsaturated derivative, and the Z to the E, in the approximate ratios of 5 3 1 for saturated, Z and E, respectively. 

Aldehydes are produced via the action of alcohol oxidizing enzymes. In those species studied, a primary alcohol oxidase which appears to require only molecular oxygen and the alcohol substrate is involved (5, 29, 33, 34). However, the action of alcohol dehydrogenases which do not require molecular oxygen to function can not be discounted where aldehydes or ketones are produced as pheromones by other insects. 

As discussed earlier, the sixteen carbon aldehydes, used as pheromone components by all Heliothis species studied to date, are formed by the action of a primary alcohol oxidase in H. virescens. 

CisHjaOj, Mr 254.41, oil. The typical basic structure of many sexual pheromones of butterflies. Particularly widely distributed are 6-, 8- and 12-, as well as (Z)-9-T. and ( )-11-tetradecenyl acetate. The corresponding fiee alcohols and aldehydes are also known as pheromones. Dodecenyl acetates (C 4Hjt02, Mr 226.36, oil) and dodecyl acetates are also widely distributed. ( -7-Dodecenyl acetate is particularly abundant and is also known as the sexual pheromone of elephants see elephant pheromone. 

The first insect pheromone to be isolated and characterized was bombykol (structure 72) from the silk moth, Bom-byx mori, by Butenandt and co-workers (Kelly, 1990), Pheromone glands (500,000) were extracted to yield 12 mg of the 4 -nitroazobenzene-4-carboxylic acid ester of the volatile alcohol. As few as 2500 molecules of the pheromone is enough to elicit behavior in the male moth (Hecker and Butenandt, 1984 Kelly, 1990). 

A number of mammalian pheromones are combinations of low-molecular-weight carboxylic acids. In other mammals, steroids, sulfur-containing compounds, amines, and alcohols play pheromonal roles some of these compounds also are derived from carboxylic acids (Albone, 1984 Harbome, 1982). Macrocyclic lactones such as civetone (77) and mus-cone (78) are the active odor compounds of the civet cat and the musk deer, respectively. 

The nomenclature of esters is relatively simple, because it is similar to the nomenclature of salts. For instance, the ester obtained from methanol and ethanoic acid (acetic acid) is called methyl ethanoate (methyl acetate). Esters are compounds that comprise a large number of structures depending on what the alcohol and acid components are. Esters with a small molecular mass are volatile substances, in most cases with a pleasant odor. For instance, butyl acetate is responsible for the odor of apples. In nature, some esters serve as pheromones for insects, for example isoamyl acetate which attracts butterflies. Other kinds of esters can be large molecules as for instanee waxes and fats where both the alcohol and the acid components can be long-ehained or eomplicated structures. These natural esters will be diseussed in the ehapter on lipids. In industry, esters are used in the fabrication of polymeric fibers for textile materials and plastic materials for various uses. The most common material is polyethylene terephthalate (PET), the ester prepared from terephthalic acid and ethylene glycol. 

The famesenes are branched hydrocarbons with four double bonds (Fig. 96.9). E.E-a-famesene and E-p-famesene are widespread in essential oils, whereas E,Z-a-famesene and Z,Z-ot-famesene are not reported to occur in nature. Z, -a-famesene is a constituent of the trail pheromone of the red fire ant. The oxidation products, famesols as primary alcohols, as well as E- and Z-nerolidol as tertiary alcohol are occasional essential oil constituents. 

Lipids are important as pheromones, precursors of pheromones, or carriers of pheromones in plants and animals. The topic has been reviewed for vertebrates and insects by Shorey (1976) and for invertebrates (mainly helminths) other than insects by Haseeb and Fried (1988). Lipophilic pheromones or their carriers are mainly glycerides, free fatty acids, and sterols. Insects excrete long-chain alcohols, alkyl acetates, aldehydes, and ketones that serve as intraspecific pheromones (Mahadevan and Ackman, 1984). 

Among the higher aldehydes ( )-2-tridecenal is responsible for the bug-like odor note in coriander seed oil (Coriandrum sativum L.) (545). In addition, ( )-2-dodecenal and ( )-2-decenal, together with the saturated members with 9 to 12 carbon atoms, were found in the same essential oil (626). It should be pointed out that the oil of coriander leaves, widely employed as a flavoring commodity in certain Eastern dishes consists of nearly 90% of aliphatic aldehydes (370). As is well known, quite a number of simple long-chain unsaturated aldehydes, alcohols and esters act as pheromones in various insects (41). 

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