Sesquiterpenes diverse production

The diverse, widespread and exceedingly numerous class of natural products that are derived from a common biosynthetic pathway based on mevalonate as parent, are synonymously named terpenoids, terpenes or isoprenoids, with the important subgroup of steroids, sometimes singled out as a class in its own right. Monoterpenes, sesquiterpenes, diterpenes and triterpenes are ubiquitous in terrestrial organisms and play an essential role in life, as we know it. Although the study of terrestrial terpenes dates back to the last century, marine terpenes were not discovered until 1955. 

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 Ci5 terpenoids known as sesquiterpenoids are the most chemically diverse group of terpenoids known in nature. Like monoterpenoids, many sesquiterpenoids contribute to the flavor and fragrances of a variety of plant products. To date about 10,000 sesquiterpenoids are known (32), and in the plant kingdom they commonly occur as hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, lactones, and oxiranes. The acyclic sesquiterpene hydrocarbons a- and p-farnesenes (HI and H2, respectively) (Fig. 8) are constituents of the oils... 

The class of natural products under focus of this work, the sesquiterpene lactones (STLs) represent one prime example, as a very large group of secondary metabolites of high diversity, with respect to chemical structure as well as biological activity. The first section of this contribution ( Structural Diversity of Sesquiterpene Lactones ) therefore focuses on a general description and discussion of STL structure in terms of chemical and biological diversity. 

The terpenoids, which are composed of the five-carbon isoprenoids, constitute the largest family of natural products with over 22,000 individual compounds in this class having been described. The terpenoids (hemiterpenes, monoterpenes, sesquiterpenes, diterpenes, triterpenes, tetraterpenes, polyterpenes, and the like) play diverse functional roles in plants as hormones, photosynthetic pigments, electron carriers, mediators of polysaccharide assembly, structural components of membranes, and defense compounds. Many compounds used by man including resins, latex, waxes, and oils contain plant terpenoids. 

MeUdwlites Some moss species contain considerable amounts of aiachidonic acid. M. form a surprising diversity of previously unknown secondary metabolites. Phenolic compounds and terpenes dominate although clear differences between the individual classes of M. are apparent. Anthocerotae are characterized by lig-nans, liverworts mainly by terpenes - mostly sesquiterpenes (often enantiomers of those occurring in higher plants) - and bibenzyl or bisbibenzyl derivatives, Musci by the occurrence of biflavonoids, sphagnorubins (peat mosses) and coumarin derivatives (Polytrichaceae). Alkaloids are very rare. Recently sterile cultures (in vitro culmres ) have been introduced to obtain the secondary metabolites from M. The production of substances corresponds qualitatively to that of M. in natural locations. 

In this instance, the sesquiterpene olefin cyclase activity could not be separated from the patchoulol synthase activity and showed similar pH and metal ion requirements, suggesting that the olefmic products are derived by diversion of the various carbocation intermediates (Cane, 1990). 

The biosynthesis of cyclic sesquiterpenes probably includes the formation of enzyme-bound intermediates (Figs. 107 and 108). It is accompanied by the shift of double bonds, hydride ions, etc. The diversity of chemical structures of sesquiterpenes is greater than that of mono-, di-, and triterpenes due to the many different types of cyclizations occuring in this group of secondary products. 

Different oleoresin terpenes have been identified in pine species (Table 136.3) [133-137]. Oleoresin obtained by tapping the bark in pine trees constitutes an important forestry product because of the chemical diversity of these secondary metabolites and their multiple possibilities of use. Oleoresin has two major fractions rosin (diterpenes), which is the solid fractiOTi, and turpentine (mono-and sesquiterpenes), which is the volatile fraction [6,40],... 

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