Sesquiterpenes representative

Differences among individuals manifest themselves not only in the main components but also in the total spectrum. The varying ratios of mono- and sesquiterpene compounds to each other demonstrate it very well individuals with 89% monoterpenes and 11% sesquiterpenes represent one marginal value, while an individual with 20% monoterpenes and 80% sesquiterpenes in the essen tial oil expressed in gas chromatography (GC) peak area percentages is the contrast. 

Harmata et al. have applied their [4+3] cycloaddition/quasi-Favorskii rearrangement to several different classes of natural products. One of these are the sterpuranes, which are sesquiterpenes represented by sterpurene 103 (Scheme 19.27) [57]. Treatment of diene 97 with a shght stoichiometric excess of 2,5-dibromocyclopentanone 98 and triethylamine using tri-fluoroethanol and benzene as the solvent resulted in the formation of cycloadduct 99. This is a relatively rare example of an intermolecular [4+3] cycloaddition in which the diene is used stoichiometrically. Typically, the diene is used in excess relative to the ally lie cation precursor. Reduction of the ketone 99 with lithium aluminum hydride, followed by treatment with potassium hydride to effect the quasi-Favorskii rearrangement, gave aldehyde 101, presumably through intermediate 100. Reduction of aldehyde 101 gave alcohol 102 in 91% yield from ketone 99. Alcohol 102 was subsequently converted into sterpurene 103. 

Although the term terpene once referred only to hydrocarbons current usage includes functionally substituted derivatives as well grouped together under the general term isoprenoids Figure 26 6 (page 1086) presents the structural formulas for a number of representative examples The isoprene units m some of these are relatively easy to identify The three isoprene units m the sesquiterpene farnesol, for example are mdi cated as follows m color They are joined m a head to tail fashion... 

If these assumptions be correct, there must be at least four natural sesquiterpenes of the caryophyllene character, namely, those represented by formulae (1) and (3), and the terp-caryophyllene and im-caryo-phyllene of Semmler. The most characteristic derivatives of the caryophyllenes are the following —... 

In 1959-61, a Czech group [8,9] reported the isolation of a new sesquiterpene lactone from Chrysanthemum (Tanacetum) parthenium as part of a study of the sesquiterpene lactones of the Compositae family. They named it parthenolide. The initial structure for parthenolide was later revised [10,11] and the accepted structure for parthenolide today is represented by structure (1). Parthenolide is a germacranolide-type sesquiterpene lactone. The crystal structure for parthenolide has also been reported [12]. Extractions of C. (T.) parthenium grown in Mexico, known locally as santamaria, did not yield parthenolide [13], but a closely related compound was isolated and named santamarine (3). This suggests that regional variations in the chemical constituents may occur. 

Overall, however, the immensity of temperate land corresponds to a most various secondary metabolic production, different from that of tropical land. The most renowned alkaloids belong to the morphine class (Chart 6.2.A1), and, in combination with isoprenoids, to the ergot and triterpene classes (Chart 6.2. A2). Prominent in the peptides are the cyclosporins (the first of which was isolated from a fiingus collected in Norway), streptogramins, and P-lactams (Chart 6.2.P). The isoprenoids are represented by pyrethrin monoterpenes, cedrane sesquiterpenes, ginkgolide and taxane diterpenes, ophiobolane sesterterpenes, and arborane and amyrin-like triterpenes (Chart 6.2.1). In the polyketides, epothilones, recently discovered from Myxobacteria, and the long known rapamycin, are two prominent classes of macrolides (Chart 6.2.FA/PO/C). 

The biological activity and toxicity of terpenoids to herbivores has been discussed (56,84) and representatives of each major type of terpene are known to be active. Well known examples are sesquiterpene lactones, pyrethrins, and several classes of diter-penes and triterpenes. 

Head-to-tail rearrangement of four isoprene units results in the formation of diterpenes (C20H32), as seen also in Fig. 4.2. Diterpenes are generally found in resins, e.g. pimaric acid and abietic acid. Some diterpenoids are also constituents of essential oils, e.g. phytol [3, 7-14, 37, 52, 53]. Like sesquiterpenes, diterpenes are heavier than monoterpenes therefore, they require more energy to go to the vapour phase. For this reason, longer distillation times are necessary for their recovery. The DNP lists 118 different structural types for diterpenoids [37]. Important diterpenes found in essential oils will be detailed. Some representatives of volatile diterpenes are as in Structure 4.32. 

Intramolecular [2 + 2] photocycloadditions of 3-alkenylcyclopent-2-enones represent the key step in the total synthesis of various natural products, e.g. pentalenolactone 6-methyl ester19 and pentalenic acid,20 as well as in the preparation of strained fenestranes21 and laurenene.22 Similarly, the photoisomerization of 3-alkenylcyclohexcnoncs to tricyclo[6.3.0.01-6]undecanones are steps in the syntheses of tricyclic sesquiterpene isocomene23 and precursors to members of the acorane family.24... 

Synthetic applications of these photocycloadditions to aromatic compounds are sometimes hampered by low chemical yields and poor selectivity in the photoreactions. However, a number of elegant syntheses of tricyclic sesquiterpenes have been hased on intramolecular 1,3-phutocycloadditions ie.g. 3. SI), and these represent a completely new approach to the preparation of such systems. 

The family Lauraceae consists of 50 genera and 2000 species of trees, shrubs, and herbs, of which 70 are of medicinal value in the Asia-Pacific region. Lauraceae are well-known for elaborating isoquinoline alkaloids and sesquiterpenes, the latter most likely representing a vast source of material for the search for NOS. Examples of such compounds are costunolide and dehydrocostunolide found in the leaves of Laurus nobilis (bay leaf, laurel), the leaves of which are widely used as a spice, antiseptic, stomachic, and to treat rheumatism in traditional European medicine (58). The potential of Neolitsea zeylanica Nees (Merr.) as a potential source of NOS inhibitor is discussed here. 

The trichothecenes, a group of sesquiterpenes having a reasonably complex tricyclic structure, represent useful targets for the synthetic application of cyclohexadienyliron complexes. Several members of... 

Nearly 40 halogenated eudesmanes and related halogenated sesquiterpenes were documented in the first survey (1), and terrestrial eudesmanes of all types are well represented with some 100 known examples (588). 

The terpenoids form a large and structurally diverse family of natural products derived from C5 isoprene units (Figure 5.1) joined in a head-to-tail fashion. Typical structures contain carbon skeletons represented by (Cs) , and are classified as hemiterpenes (C5), monoterpenes (C10), sesquiterpenes (C15), diterpenes (C2o), sesterterpenes (C25), triterpenes (C30) and tetraterpenes (C40) (Figure 5.2). Higher polymers are encountered in materials such as rubber. Isoprene itself (Figure 5.1) had been characterized as a decomposition product from various natural cyclic hydrocarbons, and was suggested as the fundamental building block for these compounds, also referred to as isoprenoids . Isoprene is produced naturally but is not involved in the formation of... 

The formation of the sesquiterpene (+)-5-epi-aristolochene (2) represents, from a biosynthetic point of view, the transformation requiring the fewest steps among those discussed in this review. A single enzyme, tobacco 5-epi-aristolochene synthase (TEAS), converts the biosynthetic precursor, farnesyl diphosphate (6), to... 

Several sesquiterpene skeletons include cyclobutane rings [78]. Some representative examples are summarized in Sch. 20. As can be easily seen, syntheses of caryophyllanes 78 and panasinsanes 79 are based on photocycloadditions to 2-methylpropene, those of tritomaranes (kelsoanes) 80, protoilludanes 81, and sterpuranes 82 are based on photocycloadditions to ethylene, while the bourbonane skeleton 83 is accessible via... 

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