Terpenes formation

The dramatic increase in terpene formation, accumulation, and emission in P. abies in response to methyl jasmonate is consistent with the effect of methyl jasmonate or jasmonic acid on many defense compounds in angiosperms. In conifers, jasmonates had been previously shown to promote the formation of heat shock and defense signaling proteins, to enhance resistance to pathogenic fimgi, and to promote colonization with ectomycorrhizae. In relation to terpenes, jasmonates had been shown to promote formation of an oxygenated sesquiterpene, todomatuic acid, and an oxygenated diterpene, paclitaxel (taxol), in cell cultures, but had never before been reported to enhance terpene accumulation in intact plants. 

To study more precisely the function of induced terpene resins in defense, it is necessary to develop a method to manipulate terpene formation without aflecting other possible defenses. For this purpose, we initiated a long-term study of the molecular biology of induced terpene biosynthesis in P. abies. The basic outline of terpene formation is well understood (Fig. 1.4). The C5 building blocks of all terpenes are synthesized via the mevalonate pathway (localized in the cytosol) from... 

Mevalonic acid, the key intermediate in solving the terpene biosynthesis pathway is an oily liquid, in solution it is in equilibrium with mevalonolactone (Figure 6.5), a crystalline solid, so the latter is used in biosynthetic studies. Fluoromevalonolactone, and the corresponding acid, are powerful inhibitors of terpene formation. If addition of fluoromevalonate to a biosynthesizing system blocks the formation of a compound, then it can be concluded that that compound has a terpene origin. 

Other catalytic applications of HBF4 include alkene isomerizations, alkylation of alcohols with diazoalkanes, preparations of substituted pyridines, hydrolysis of a-hydroxyketene or a-(methylthio)ketene thioacetals to a,p-unsaturated thioesters, and terpene formation from isoprenic precursors. ... 

Carbon-Carbon Bond Formation in Terpene Biosynthesis... 

CARBON-CARBON BOND FORMATION IN TERPENE BIOSYNTHESIS... 

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... 

Since GAs as diterpenes share many intermediates in the biosynthetic steps leading to other terpenoids, eg, cytokinins, ABA, sterols, and carotenoids, inhibitors of the mevalonate (MVA) pathway of terpene synthesis also inhibit GA synthesis (57). Biosynthesis of GAs progresses in three stages, ie, formation of / Akaurene from MVA, oxidation of /-kaurene to GA 2" hyde, and further oxidation of the GA22-aldehyde to form the different GAs more than 70 different GAs have been identified. 

Cycloahphatics capable of tertiary carbocation formation are candidates for nucleophilic addition of nitriles. HCN in strong sulfuric acid transforms 1-methyl-1-cyclohexanol to 1-methyl-1-cyclohexylamine through the formamide (47). The terpenes pinene (14) [2437-95-8] and limonene [5989-27-5] (15) each undergo a double addition of HCN to provide, after hydrolysis, the cycloahphatic diamine 1,8-menthanediamine (16) (48). 

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

It yields a chloride, thujyl chloride, Cj H jCl, by the action of phosphorus pentachloride, which on treatment with aniline yields up HCl, with the formation of the terpene thujene. 

Problem 27.7 Propose mechanistic pathways for the biosynthetic formation of the following terpenes ... 

Properties of Latia luciferin. Latia luciferin is a highly hydrophobic, fat-soluble compound, and volatile under vacuum. It is a colorless liquid, with an absorption maximum at 207nm (s approx. 13,700 Fig. 6.1.2). The chemical structure of Latia luciferin has been determined to be 1 (C15H24O2), an enol formate of a terpene aldehyde 3 (Fig. 6.1.3 Shimomura and Johnson, 1968b). The enol formate group of Latia luciferin is unstable the luciferin is spontaneously hydrolyzed... 

It is immediately clear that Acanthomyops need not rely on dietary sources of terpenes but can synthesize citronellal and citral from either acetate or mevalonate. The higher total activity of the citronellal as compared with the citral probably reflects the natural preponderance of citronellal (ca. 90%) in the ant secretion. As the specific activities show, these results are consistent with a common biogenetic origin of both terpenes. In the mevalonic acid pathway as described from other organisms (13), the radioactive carbon of l-C14-mevalonate is lost upon formation of isopentenyl pyrophosphate. 

Some representative Claisen rearrangements are shown in Scheme 6.14. Entry 1 illustrates the application of the Claisen rearrangement in the introduction of a substituent at the junction of two six-membered rings. Introduction of a substituent at this type of position is frequently necessary in the synthesis of steroids and terpenes. In Entry 2, formation and rearrangement of a 2-propenyl ether leads to formation of a methyl ketone. Entry 3 illustrates the use of 3-methoxyisoprene to form the allylic ether. The rearrangement of this type of ether leads to introduction of isoprene structural units into the reaction product. Entry 4 involves an allylic ether prepared by O-alkylation of a (3-keto enolate. Entry 5 was used in the course of synthesis of a diterpene lactone. Entry 6 is a case in which PdCl2 catalyzes both the formation and rearrangement of the reactant. 

Longifolene is a tricyclic sesquiterpene. It is a typical terpene hydrocarbon in terms of the structural complexity. The synthetic challenge lies in construction of the bicyclic ring system. Schemes 13.24 through 13.33 describe nine separate syntheses of longifolene. We wish to particularly emphasize the methods for carbon-carbon bond formation used in these syntheses. There are four stereogenic centers in longifolene,... 

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