Terpenes basic structure

About 30 000 terpenes are known at present in the literature Their basic structure follows a general principle 2-Methylbutane residues, less precisely but usually also referred to as isoprene units, (Cs), build up the carbon skeleton of terpenes this is the isoprene rule found by Ruzicka and Wallach (Table 1). Therefore, terpenes are also denoted as isoprenoids. In nature, terpenes occur predominantly as hydrocarbons, alcohols and their glycosides, ethers, aldehydes, ketones, carboxylic acids and esters. 

Biaryl structures are wide-spread in many of naturally occuring products including alkaloids, lignans, terpenes, flavonoids, tannins, as well as polyketides, coumarins, peptides, glycopeptides, etc. For example, vancomycin (1) is a basic structure of several related glycopeptide antibiotics [1] balhimycin, actinoidin A, ristocetin A, teicoplanin A2-2, complestatin, etc which are important in medicinal chemistry or as a HPLC chiral stationary phases (vancomycin) [2]. 

Terpene compounds were also examined for inducing activity because they, like the steroids, are isoprene derivatives, although representing simpler molecules than the steroids. The basic structural... 

Terpene compounds have natural occurrence in plants found as major components of most of the plant essential oils. Based on their structural and functional properties, terpene compounds have been classified according to their basic structural unit isoprene containing five carbons, fii the formation of terpenes, prenyldi-phosphate serves as a precursor. The terpene compounds exist in the form of mono-, sesqui-, hemi-, di-, tri-, and tetraterpenes. The mmioterpenes containing two isoprene units are responsible to cmistruct the major portion of all the essential oils. These compounds work as carbure, alcohol, aldehyde, ketone, ester, ether, peroxyde, and phenols [58]. The sesquiterpene compounds contain three isoprene units, and the functional properties are very close to monoterpene compounds. 

The chiral leaving group-Lewis acid combined system is also effective for the enantioselective synthesis of carbocyclic compounds which have the basic structure of terpenes without possessing remarkable functionalized groups [63]. They successfully applied this method to produce (+)-(J )-limonene from the corresponding allylic ether in two steps, obtaining an overall yield of 77%. (Scheme 10.38). 

Alkaloids, nitrogen-containing compounds generally found as secondary metabolites in plants, are also classical examples of renewables. In contrast to terpenes, they show a great variety in molecular structure, and the different classes of alkaloids are usually based on their basic ring systems. Many pharmaceutically active... 

Two entirely different approaches to systematizing the numberings of the basic monocyclic and bicyclic terpene structures were suggested in 1952 by G. M. Dyson of England and N. E. Wolff of Princeton University. It was the opinion of the American committees that these proposals needed considerable developmental work by their proponents before they could be properly evaluated. 

If as above we simply represent alicyclic rings sharing two Gs by a vertical line, then we can represent the basic tetracyclic structure of lanosterol as G61G61 G6 C5 (noting that there are two double bonds and various alkyl substituents and also a 3-hydroxyl on the first of the alicyclic rings). Many subsequent reactions yield cholesterol, a major triterpene membrane component that modifies the fluidity of animal cell membranes and is a precursor for synthesis of animal bile acids (fat solubilizing amphipathic detergents) plant triterpenes and steroid hormones such as the corticosteroids cortisol and cortisone, the mineralocorticoid aldosterone and the sex hormones testosterone and 17-(3-oestradiol. The structure and bioactivity of the plant terpenes is sketched below. 

The bisabolyl cation (P10.1) is the key intermediate in the biosynthesis of the bergamotane, a- and (3-santalane families of terpenes. The biogenetic reactions involved in converting (P10.1) to the final products, are all enzyme mediated, but their chemistry follows the basic principles of carbocation mechanisms. Draw mechanisms to account for the formation of a-bergamotene (P10.2), a-santalene (P10.3) and (3-santalene (P10.4) from the cation (P10.1) and propose a structure for the intermediate (X) (Figure P10). 

Among the worldwide total of 30000 known natural products, about 80% stems from plant resources. The number of known chemical structures of plant secondary metabolites is four times the number of known microbial secondary metabolites. Plant secondary metabolites are widely used as valuable medicines (such as paclitaxel, vinblastine, camptothecin, ginsenosides, and artemisinin), food additives, flavors, spices (such as rose oil, vanillin), pigments (such as Sin red and anthocyanins), cosmetics (such as aloe polysaccharides), and bio-pesticides (such as pyrethrins). Currently, a quarter of all prescribed pharmaceuticals compounds in industrialized countries are directly or indirectly derived from plants, or via semi-synthesis. Furthermore, 11% of the 252 drugs considered as basic and essential by the WHO are exclusively derived from plants. According to their biosynthetic pathways, secondary metabolites are usually classified into three large molecule families phenolics, terpenes, and steroids. Some known plant-derived pharmaceuticals are shown in Table 6.1. 

However, oils occur in much greater concentrations in fruits and seeds. The so-called essential oils are usually sweet, or aromatic smelling organic compounds which may also contain sulfur and nitrogen in addition to the usual carbon and hydrogen. These oils are often of the terpene class with the general formula (C5Hg) , where n > 1, or may be compound types similar to camphor or other oxidation products associated with the basic terpene structure. 

The basic skeleton of isoprenoids may be modified by the introduction of a wide variety of chemical groups, by isomerization, shift of double bonds, methyl groups, etc. Hence a bewildering number of chemical structures arises. In addition compounds derived from other biogenic pathways may contain isoprene residues. For instance the K vitamins (D 8.1), ubiquinones (D 8.3), chlorophylls (D 10.1), plastoquinones, and tocopherylquinones (D 22.4) have isoprenoid side chains with up to ten isoprene units. Polyketides (D 3.3), alkaloids (D 8.4.2), and coumarins (D 22.2.2) may be substituted by dimethylallyl groups. The terpene residues are attached to nucleophilic sites, such as active methylene groups and phenolic oxygen atoms. 

All living organisms produce terpenes for some essential physiological functions including some defense mechanisms for many plants. The enormous number and diversity of structures of terpenoids exist which is attributed to the fact that there are many ways in which the basic C5 units can be combined together and there are... 

Terpenes are hydrocarbon compounds through the condensation of several isoprene units. Terpenoids, in fact, are modified terpenes, wherein some methyl groups have been removed or replaced, often oxygen atoms added. Most of them are multicyclic structures which differ from one another not only in their basic carlxMi skeletons but also in functional groups. The structural unit of terpenoid building blocks is isopentenyl pyrophosphate (IPP). 

Naturally, the pulp yield is reduced in relation to the amount of non-structural material present in the wood. If the extractives content is high and the lignin content is normal, the pulp yield will be correspondingly lower. The basic density of the wood and its extractives content are the two most important parameters for predicting the yield and quality of kraft pulp from eucalypts (57, 67). If the extractives - such as terpenes - are inert to the pulping conditions, there may be no other effect. However, most extractives react with pulping chemicals, and occasionally with the cell wall components, so as to affect further pulp yield and quality (see Sect. 9.3.4). 

Depending on their structure, hydrocarbons occurring in foods can be divided into three basic groups aliphatic, aKcycHc and aromatic hydrocarbons. The most important flavour-active substances (in addition to natural dyes) are terpenic hydrocarbons (terpenes). 

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