Myrcene precursor

Byers J. A. and Birgersson G. (1990) Pheromone production in a bark beetle independent of myrcene precursor in host pine species. Naturwissenschaften 77, 385-387. 

Attempts to investigate boll weevil (Anthonomus grandis) pheromone biosynthesis have identified isomerization, dehydration, and oxidation of the pheromone alcohols, and anticipated allylic oxidation of myrcene and limonene, but no evidence for the cyclization of acyclic precursors. The aggregation pheromones of bark beetles have been reviewed. Ips calligraphus responds to ipsdienol only in the presence of the c/5-verbenol (32) large additional concentrations of the enantiomer (l/ ,4i ,5/ )-(32) reduce beetle response. 5-(-)-Ipsenol, the pheromone of Ips grandicollis, increases the response of /. avulsus to its own pheromone ipsdienol. ... 

Detailed investigations of myrcene in hydroformylation reactions were made by Gusevskaya [45], The reaction led to nine products the major products are shown in Scheme 15. Different precursors and ligands were studied in this reaction. 

The faecal pellets of the bark beetle Ips paraconfusus which had fed on the phloem of Pinus ponderosa contained large quantities of the aggregation pheromones cis-verbenol (24), ipsenol (25), and ipsdienol (26). The pheromones originate in the hindgut, but, although there is a precursor-product correlation between a-pinene or myrcene from the phloem and the pheromone terpenoids, the biosynthetic site is unclear. The demonstration68 of the conversion of a-pinene into cis- and trans-verbenol (27) by Bacillus cereus found in the gut of I. paraconfusus has led to the... 

Routes to furan monoterpenes from other monoterpenoids are well known, and the photooxygenation route from myrcene (7) to perillene (849) was discussed in Vol. 4 (p. 561). Using the aldehyde 863 led, by the same route ( 62, then ferrous ion) to perillenal (846). The simplest reported preparation of perillene (849) from a dimethyloctane monoterpenoid precursor is certainly the autoxidation of citral enol acetates (864), yielding 11% of a mixture of perillene (849) and rose furan (848) after passing air through a chloroform solution for 24 hours. 

Monoterpene biosynthesis has been studied in conifers using labeled precursors such as carbon dioxide, acetate and mevalonate (63,64). Specifically labeled precursors have been employed to deduce mechanistic features of a-plnene (65,66) and 3-carene (67,68) biosynthesis in pine species. Glelzes and co-workers (69) have argued, by way of time-course studies, that the initial formation of acyclic hydrocarbons (oclmene, myrcene) from C02 in Pinus pinaster needles indicated that these olefins serve as precursors to cyclic monoterpenes (a-plnene, 8-pinene) by a reversible protonatlon mechanism. These suggestions, however, are without precedent, and run counter to direct evidence demonstrating that the cyclizatlon of geranyl pyrophosphate occurs without the involvement of free intermediates (17). 

Most pheromones are synthesized de novo in the animal body. Some, however, are taken up from plant sources and are used directly or in a modified form (cf. the pyrrolizidines secreted as sex pheromones from male Danaid butterflies and myrcene used as sex pheromone of Dehdroctonus brevicomis Table 66). In Creatonotos moths, pyrrolizidine alkaloids ingested by the larvae with the diet, in addition to their action as pheromone precursors, show hormone-like activity and control the morphogenesis of the scent organs. 

A range of monoterpenes has been identified from Nasutitermes species (Prestwich, 1979 Baker and Walmsley, 1982) of which a-pinene, /J-pinene, limonene, terpinolene, and myrcene are the most common. In Trinervitermes gratiosus, intraspecific variations occur (Prestwich, 1978) in allopatric populations from Kenya. Major soldiers produce a-pinene. Minor soldiers from two populations produce a-pinene, -pinene, camphene, and limonene, but only a-pinene in the other group. More pronounced variations occur in the diterpenes, and populations of this species and T. bettonianus (Prestwich and Chen, 1981) are easily distinguished on the basis of the diterpene profiles of major and minor soldiers (Fig. 16.15). These population differences are not due to diet, and injection of labelled precursors (Prestwich et al., 1981) into Nasutitermes octopilis has demonstrated that the soldiers are capable of synthesizing the mono- and diterpenoid components of their secretion. 

Several forms of aging of SOA vapors have been observed. One clear form is oxidation of multiply unsaturated alkenes. Many terpenes have multiple unsaturations, and in some cases different double bonds have very different rate constants for reaction with ozone. Examples include terpinolene, myrcene, hmo-nene, a-humulene, and p-caryophyllene [149, 150]. In these systems, ozone will react with one double bond in the terpene and produce some SOA. However, after the precursor is completely removed, SOA levels can continue to rise as the first-generation semi-volatile products continue to react with ozone to produce less volatile second-generation products [149]. 

Natural (-)-menthol is synthesised commercially on a multi-ton scale from the inexpensive achiral precursor myrcene in an elegant application of the asymmetric 1,3-hydrogen shift (see section 6.4.2). The synthesis is so good that it competes with the traditional isolation method from oil of wintergreen. 

Myrcene (32) is also koown as p-myrcene and its systematic name is 7-methyl-3-methylene-l,6-octadiene. It is very widespread in nature. This is not surprising as it is formed in nature by elimination from geranyl pyrophosphate, the precursor of all monoterpenoids. It can also be formed by elimination of water from alcohols such as geraniol or linalool, and so its presence in namral extracts may be as an artifact (formed during the extraction process) rather than as a genuine plant metabolite. 

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