Monoterpenes biosynthesized

Terpenes (and terpenoids) are further classified according to the number of 5-carbon units they contain. Thus, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, sesquiterpenes are 15-carbon molecules from three isoprene units, diterpenes are 20-carbon substances from four isoprene units, and so on. Monoterpenes and sesquiterpenes are found primarily in plants, but the higher terpenoids occur in both plants and animals, and many have important biological roles. The triterpenoid lanosterol, for example, is the precursor from which all steroid hormones are made. 

Previously, the 14C-labeled mevalonic acid (12) was shown to be incorporated into the acid moiety [28, 29]. However, monoterpenes are generally biosynthesized via the MEP but not the mevalonate pathway. Hence, the author employed [1-13C] D-glucose (Fig. 2) as the precursor to examine whether the acid moiety is produced... 

Whereas some species oxidize host terpenes more randomly, producing an array of rather unspecific volatiles with little information, others use highly selective enzyme systems for the production of unique olfactory signals. However, apart from transformations of monoterpene hydrocarbons of host trees, oxygenated monoterpenes may well be biosynthesized de novo by the beetles (see below). 

It is well known that the steroid hormones in mammals are biosynthesized from cholesterol. This compound is derived from the acetate-mevalonate pathway through the monoterpene geranyl pyrophosphate, which undergoes several enzymatic reactions to form the triterpene squalene. 

Section 26.8 X fi-Thujone a toxic monoterpene present in absinthe Terpenes and related isoprenoid compounds are biosynthesized from isopentenyl pyrophosphate. 

Figure 6.11 Biosyntheses of isoprenoid pheromone components by bark and ambrosia beetles from host conifer monoterpenes. (A) Conversion by the male California fivespined ips, Ips paraconfusus Lanier (Coleoptera Scolytidae), of myrcene from the xylem and phloem oleoresin of ponderosa pine, Pinus ponderosa Laws., to (4S)-(+)-ipsdienol and (4S)-(-)-ipsenol, components of the aggregation pheromone (Hendry et al., 1980). (B) Conversion by male and female I. paraconfusus of (1 S,5S)-(-)-a-pinene (2,6,6-trimethyl-bicyclo[3.1,1]hept-2-ene) from the xylem and phloem oleoresin of P. ponderosa to (1 S,2S,5S)-(+)-c/s-verbenol (c/s-4,6,6-trimethyl-bicyclo[3.1,1]hept-3-en-2-ol), an aggregation pheromone synergist and of (1 R,5R)-(+)-a-pinene to (1 fl,2S,5fl)-(+)-frans-verbenol (frans-4,6,6-trimethyl-bicyclo[3.1,1]hept-3-en-2-ol), a compound of unknown behavioral activity for /. paraconfusus. Male and female western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera Scolytidae), convert (1 S,5S)-(-)-a-pinene to (1S,2ft,5S)-(-)-frans-verbenol, an aggregation pheromone interruptant and (1R,5R)-(+)-a-pinene to (1 R,2S,5R)-(+)-frans-verbenol, a compound of...

Terpenes are classified according to the number of isoprene units they contain. Thus, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, sesquiterpenes are 15-carbon molecules from three isoprene units, and so on (Table 27.3). 

Terpenes are most familiar, at least by odor, as compounds of the so-called essential oils obtained by steam distillation or ether extraction of various plants. Thousands of different terpenes are known. According to the isoprene rule proposed by L. Ruzicka in 1921, they can be considered to arise from head-to-tail joining of simple five-carbon isoprene (2-methyl-1,3-butadiene) units. Terpenes are subdivided into groups depending on the number of isoprene units [9]. For example, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, which can be divided into aliphatic, monocyclic, or bicyclic species Some typical exponents of each monoterpene subgroup are shown in Fig 1... 

Terpenes are are a class of compounds whose chemical structures are based on a number of isoprene units , derived from the hydrocarbon CH2=C(CH3)-CH=CH2 they may themselves be hydrocarbons, but may also contain alcohol (OH), aldehyde/ketone (CO) and carboxylic acid (COOH) groups. Monoterpenes are Cm compounds derived from two isoprene units, sesquiterpenes (Cu) are derived from three isoprene units, diterpenes (C20) from four and tritepenes (C30) from six. Terpenes are widespread in plants, where they are largely responsible for the odor, and they are the major constituents of plant-derived essential oUs . Among the best known terpenes are 3-pinene (turpentine), camphor, menthol and citroneUal (aU monoterpenes) and farnesol (a sesquiterpene that is a constituent of the essential oils of many plants). Certain terpenes have important biological roles vitamin A, for example, is a diterpene, and steroid hormones have a structure related to triterpenes (and are biosynthesized by a similar route). 

The biosyntheses of other monoterpene hydrocarbons, such as those of sabinene, and (-t-)-car-3-ene, are considered to involve the cyclization of such cyclohexenyl homoallyl cations to three-membered ring derivatives. ... 

Tissue Cultures, Microbial Transformations.—Little success has rewarded the search for cell cultures that effectively biosynthesize monoterpenes de novo. The most impressive studies utilize cultures from a variety of Mentha spp. yields of oil were some 60 % (w/v) of those in the parent plants, but the monoterpene products were generally more oxidized (i.e. ketones extra C=C bonds predominated). In vitro, oxidation at C-3 of the menthane skeleton was also restricted, apparently owing to an inhibition of the enzymic reduction of the 4(8) double bond in the intermediates formed.925 926 Colchicine stimulated synthesis of essential oil by Mentha cultures.927 Iridoid glucosides have been produced by cultured cells of Gardenia spp.673 Menthone was biotransformed to neomenthol by Mentha suspension cultures,928 and Nicotiana lines oxidized linalool and its derivatives at C-10 to aldehydes and alcohols,929 and also foreign substrates such as a-terpineol (at C-6 and C-7) and /raw.s-/ -menthan-9-en-l-ol (at C-4 and C-10).930... 

Formation and metabolism of monoterpenes by yeasts. Although certain species of yeasts are capable of producing monoterpenes (80,81), the wine yeast species Saccharomyces cerevlslae appears not to share this capacity (82). Accordingly, it has been concluded that terpene composition in various grape cultivars and varietal wines is not Influenced by fermentation (6,82). Although apparently unable to biosynthesize monoterpenes, wine yeasts may carry out certain transformations of these compounds (e.g. double bond reduction) (83). 

The methylcyclopentanoid monoterpenes arise from geranyl-PP via an intramolecular stereocontrolled Mannich type condensation of a dialdehydic or a trialdehydic intermediate, as shown in fig.4. The resulting cyclopentanaldehydic compound has been named iridodial or iridotrial, depending on the nature of the biosynthesized compound and of its biogenetic pathway. 

The parent compound of the S. is secologanin, a key compound in the biosyntheses of most indole alkaloids, the Cinchona, ipecac, and pyrroloquinoline alkaloids as well as simple monoterpene alkaloids. Over 1000 indole alkaloids are formed from secologanin in vivo - comprising almost a quarter of this large group of natural products. 

The stmcture of presqualene resembles that of chrysan-themic acid (11), a monoterpene acid found in pyrethrins (Fig. 23.3) that may be biosynthesized from two moieties of dimethylallyl pyrophosphate (DMAPP) in a fashion analogous to the formation of presqualene pyrophosphate (Poulter, 1990 Poulter and Rilling 1981). 

T.a. are biosynthesized from mevalonic acid, but the origin of the nitrogen is not known. They therefore differ from the iridoid, isoquinoline and indole alkaloids, in which a monoterpene is linked to an amino acid. 

Thiols in Biochemistry.—Monoterpene keto-thiols (28, and the m-isomer) are the first of their type to appear in Nature. The major interest in biosynthesized thiols remains within the polypeptide field, and the identification, reactivity, and function of cysteine residues in polypeptides and proteins feature prominently in the literature. 

Conifer resin, which is a mixture of monoterpenes and diterpenes is an important protective compound against bark beetles and other conifer herbivores. The volatile monoterpenes emanating from a specific tree is often the cue for bark beetles to find a tree where the tree defenses could be compromised from abiotic or biotic stresses. The synchronized mass attack is the strategy bark beetles use to reduce the effects of resin-based defenses in conifers. Aggregation hormones released by bark beetles are oxidized monoterpenoids such as ipsdienol, ipsenol and verbenol. It is believed that these compounds can be oxidation products of host plant monoterpenes such as myrcene. Recently it has been observed that most of the monoterpenoid aggregation pheromone components are biosynthesized de novo in bark beetles [7]. 

This complexity of EOs phytochemistry led to a certain inconsistency of the chemical composition of an essential oil. In fact, several factors influence the balance of the compounds within EOs. Terpenoids and isoprenoid are synthesized through secondary metabolism of the plant. Monoterpenes are biosynthesized in plastid via two 5-carbon precursors, that is, isopentenyl pyrophosphate and dimethylallyl pyrophosphate, which condense to give the monoterpenes (10-carbon). The sesquiterpenes (15-carbon) are formed via the mevalonate pathway in the cytosol. Phenylpropanoids are derived mainly from the shikimate pathway [5]. 

The biosyntheses of terpenes belong to the most diverse strategies developed by nature. As mentioned earlier at Chapter 5, just two simple building blocks (compounds 1 and 2) are necessary to generate a fascinating diversity of different (biologically relevant) molecules. With respect to the syntheses of monoterpenes, the three isomeric diphosphates 3-5 are the stractural key intermediates. By rather... 

With respect to the biosyntheses of menthane-type monoterpenes, the menthyl cation C can either lose a proton resulting in the formation of Umonene (16), or it may be directly attacked by H O to give a-terpineol (17), which can... 

Limonene (16) can also serve as the starting material for a series of further transformations to obtain such important oxygenated monocyclic monoterpenes like menthol (38) or others as shown in Scheme 6.7. These are further impressive examples how nature can anploy rather simple molecules like 16 that contain at least two activated sites for further enzyme-catalyzed transformations to get access to a very diverse assembly of different metabohtes. Hereby, allyUc oxidations and subsequent (stereoselective) redox state manipulations as well as isomerization reactions are the main chemical transformations. Further dehydrogenation reactions of either limonene or advanced oxygenated monocyclic terpenes can also lead to an aromatization giving access to a small group of aromatic compounds (e.g., p-cymene (39) or thymol (40)) that are not biosynthesized by more common pathways like the shikimic acid pathway [1,3]. 

Cramer, F., und W. Rittersdorf Die Hydrolyse von Phosphaten und Pyrophospha-ten einiger Monoterpenalkohole. Modellreaktionen zur Biosynthese der Monoterpene. Tetrahedron 23, 3015 (1967). 

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