Terpenes monoterpenes

The root of carrot Daucus carota) is eaten raw or cooked. The characteristic aroma and flavour of carrots are mainly due to volatile compounds, although non-volatile polyacetylenes and isocoumarins contribute significantly to the bitterness of carrots [1,2]. More than 90 volatile compounds have been identified from carrots (Table 7.9) [207-215]. The carrot volatiles consist mainly of terpenoids in terms of numbers and amounts and include monoterpenes, sesquiterpenes and irregular terpenes. Monoterpenes and sesquiterpenes account... 

Kubeczka (J58) utilized this general approach to separate a terpene mixture Into oxygenated terpenes, monoterpene hydrocarbons and sesquiterpene hydrocarbons fractions before a final analytical separation. He used a C-18 reverse phase system operated in the semi preparative mode to obtain h1s preliminary separations. The sample fractions were then analyzed by liquid-solid chromatography using deactivated silica gel (4.8% water/n-pentane) at -15 °C. 

The isoprene molecules are usually (though not always) joined head-to-tail. The simplest terpenes (monoterpenes) are the chief constituents of the essential volatile oils obtained from the sap and tissues of certain plants and trees. These have been used in the manufacture of perfumes from earliest times. In particular, the monoterpenes extracted from pine trees, or obtained as by-products in paper pulp manufacture, have been used for many years as paint solvents (Chapter 9) and anti-oxidants (Chapter 10). 

Isoprene is a hydrocarbon and is the basic building block of many essential oils, either in the form of a terpene or in an oxygenated form (e.g., alcohol, aldehyde, etc.). The components of an essential oil can be roughly classed into the following types terpenes (monoterpenes and sequiterpenes), oxygenated compounds, alcohols, phenols, aldehydes, ketones, esters, lactones, coumarins, ethers, and oxides. 

Keywoids. Terpene, Monoterpene, Sesquiterpene, Diterpene, Cyclase, Geranyl diphosphate, Farnesyl diphosphate, Geranylgeranyl diphosphate... 

Most essential oils contain a significant proportion of terpenes (monoterpenic and sesquiterpenic hydrocarbons). For example, their level in some citrus essential oils is 95% or more. These substances are not usually essential to the smell and aroma character of essential oils, as the most important odoriferous compounds are alcohols, aldehydes, ketones, esters and other compounds. Furthermore, terpenic hydrocarbons are a reason for the limited solubility of essential oils in diluted ethanol and are often the cause of deterioration of essential oils that easily oxidise or polymerise. By removing hydrocarbons from essential oils, concentrates are obtained. Monoterpene-free or sesquiterpene-free essential... 

Problem 11.2 Classify the following terpene (monoterpene, diterpene, etc.) and indicate its division into isoprene units. Then, identify the conjugated double bonds. 

The enzyme catalyzed reactions that lead to geraniol and farnesol (as their pyrophosphate esters) are mechanistically related to the acid catalyzed dimerization of alkenes discussed m Section 6 21 The reaction of an allylic pyrophosphate or a carbo cation with a source of rr electrons is a recurring theme m terpene biosynthesis and is invoked to explain the origin of more complicated structural types Consider for exam pie the formation of cyclic monoterpenes Neryl pyrophosphate formed by an enzyme catalyzed isomerization of the E double bond m geranyl pyrophosphate has the proper geometry to form a six membered ring via intramolecular attack of the double bond on the allylic pyrophosphate unit... 

Terpenes, specifically monoterpenes, are naturally occurring monomers that are usually obtained as by-products of the paper and citms industries. Monoterpenes that are typically employed in hydrocarbon resins are shown in Figure 2. Optically active tf-limonene is obtained from various natural oils, particularly citms oils (81). a and P-pinenes are obtained from sulfate turpentine produced in the kraft (sulfate) pulping process. Southeastern U.S. sulfate turpentine contains approximately 60—70 wt % a-pinene and 20—25 wt % P-pinene (see Terpenoids). Dipentene, which is a complex mixture of if,/-Hmonene, a- and P-pheUandrene, a- and y-terpinene, and terpinolene, is also obtained from the processing of sulfate Hquor (82). 

Terpenes (Section 26.7) Compounds that can be analyzed as clusters of isoprene units. Terpenes with 10 carbons are classified as monoterpenes, those with 15 are sesquiterpenes, those with 20 are diterpenes, and those with 30 are triterpenes. 

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. 

The use of volatile chemicals as systematic markers has the obvious advantage of lending itself to quantification through GLC. In many, if not most, of the cases discussed below, qualitative differences in monoterpene profiles would not have been sufficient to allow distinctions to be made between taxa, or even between individuals within a population. This is true because most conifers synthesize many of the same monoterpenes, although often in vastly different relative concentrations. It is these quantitative differences that have been constructively used in the following examples. Structures of the terpenes commonly studied are presented in Fig. 3.7. 

Genetics of terpenes. II. Genetic variatnces and interrelationships of monoterpene... 

Hoffmann and coworkers have elaborated an appealing three-component domino Knoevenagel/hetero-Diels-Alder procedure [395]. These authors converted cy-clohexane-l,3-dione, formaldehyde and several as dienophiles acceptor serving monoterpenes into a variety of polyketide terpenes of type 2-790 (Scheme 2.175). 

The three classes of terpenes have different temperature profiles. These differences can be related to their boiling points, which are related to their molecular weight and their number of carbons [49]. Monoterpenes are highly volatile compounds (limonene bp763... 

B. frereana and B. papyrifera olibanum have very different terpenic composition from the others. B. frereana olibanum contains the same monoterpenes as olibanum from B. carteri, B. sacra or B. serrata, but is very poor in sesquiterpenes and contains none of the diterpenic biomarkers cited before. Two unidentified compounds (55 and 56) seem to be specific and the main diterpenes, present in high level, are four dimers of a-phellandrene. Dimer 3 (113) is the major component. On account of its absence in the other olibanum samples, it can be considered as characteristic of B. frereana olibanum. 

From their carbon skeletons terpenes can be seen as isoprene (C5) oligomers. Terpenes are classified according to their number of isoprene units as monoterpenes (C10), sesquiterpenes (Q5), diterpenes (C2o), etc. /1-Carotene (1) is a tetrater-pene. 

In order to obtain lactones from natural alkenols, we investigated the cyclocarbonylation of monoterpenic alcohols. The catalytic precursor is [PdCl2L2] in the presence of a slight excess of tin chloride and phosphine ligands. Dihydromyrcenol, a representative acyclic terpene containing a termi-... 

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). 

Oxygenated monoterpenes which are found in almost every bark beetle species attacking coniferous trees, include czs-verbenol 246, frans-verbenol 247, and myrtenol 248, representing primary products of allylic oxidation of the host terpene a-pinene 45. Further oxidation of 247 or 248 leads to the... 

In European Reticulitermes termites however, 16 known terpene compounds were isolated from the soldier frontal gland secretion, including monoterpenes, sesquiterpenes, diterpenes, and one sesterterpene [184]. 

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