Terpenoid quinones

Since carotenoids are isoprenoids, they share a common early pathway with other biologically important isoprenoids such as sterols, gibberellins, phytol and the terpenoid quinones (Fig. 13.3). In all cases, these compounds are derived from the C5 isoprenoid, isopentenyl diphosphate (IPP). Until a few years ago it was believed that a single pathway from the Cg precursor mevalonic acid (MVA) formed IPP, which itself was synthesised from hydroxymethylglutaryl coenzyme A (HMG CoA) by the action of HMG... 

Since carotenoids are derived for the central isoprenoid pathway (Fig. 13.3), the regulation of their formation must involve a co-ordinated flux of isoprenoid imits into this branch of the pathway as well as into others such as the biosynthesis of sterols, gibberellins, phytol and terpenoid quinones. An imderstanding of the complexities of regulation of the pathway is necessary in order to target the regulatory steps for genetic manipulation. 

Hirose, Y. Hasegawa, S. Ozaki, N. Three new terpenoid quinone methides from the seed of Chamaecyparis obtusa. Tetrahedron Lett. 1983, 24, 1535-1538. 

E) coumarins, (F) quinones, (G) flavonoids, (H) tannins, (I) alkaloids, (J) terpenoids and steroids and (K) miscellaneous and unknowns. Although many of these compounds are secondary products of plant metabolism, several are also degradation products which occur in the presence of microbial enzymes. 

TA in wild cottons. Many wild cottons have TA contents similar to those of G. barbadense. Thus, 30-80% methylation of terpenoids and a predominance of ocimene-derived heliocides also occurs in anomalum. . bickii. . capitis-viridis. G. darwinii. lonoicalvx. G. tomentosum and G. sturtianum (121. In the latter two species, the TA quinone concentrations are much greater than the heliocide concentrations, indicating that very little ocimene or myrcene is formed in these species. 

Bacteria overall > 410 Groom, 1992 Scarce diversification between land and sea. ALKAL. indole, phenazine, pyperazine, pyrrole, polypyrrole. PEPT. various classes, including siderophores. POLYKET. lactones, macrolides, quinones. CARBOH. (amino)glycoside, terpenoids hi hi ... 

Porif.> (hydro)pyrimidine, macroQ clic and oligomeric pyridine or pyridinium, naphthyridine, oxazole, pteridine, pyridoacridine, pyrrole, pyrroloimiiMquinone, (oxa)quinoli2idine, terpenoid indolizidine. ISOPR. Monotero. rare Sesouitem. . Ditero.. Sestertero. also degraded C>i Tritero.. POLYKET. macrolides, polyacetylenes, polycyclic (hydro)quinones, polyethers, (epidioxy)polyp ionates. ... 

There are diffent pathways by which all phenolic compounds are synthesized [6,7]. The shikimate/arogenate pathway leads, through phenylalanine, to the majority of plant phenolics, and therefore we shall centre the present revision on the detailed description of this pathway. The acetate/malonate pathway leads to some plant quinones but also to various side-chain-elongated phenylpropanoids (e.g. the group of flavonoids). Finally, the acetate/mevalonate pathway leads by dehydrogenation reactions to some aromatic terpenoids. 

Terpenoid fragments containing several iso-prene units are found as alkyl substituents in shikimate-derived quinones (see page 158). Thus ubiquinones typically have C40—C50 side-chains,... 

The terpenoid benzo[fc]thiophen-4,7-quinone (3) has been isolated10 from the extremely thermophilic and acidophilic bacterium Caldariella acidophila. Desulphurization with Raney nickel gave the ethyl, C30-alkyl disubstituted 1,4-benzoquinone (4). The compound (3) may be involved in the electron-transport system of the organism. 

Like chlorophyll, plastoquinone A has a nonpolar terpenoid or isoprenoid tail, which can stabilize the molecule at the proper location in the lamellar membranes of chloroplasts via hydrophobic reactions with other membrane components. When donating or accepting electrons, plastoquinones have characteristic absorption changes in the UV near 250 to 260, 290, and 320 nm that can be monitored to study their electron transfer reactions. (Plastoquinone refers to a quinone found in a plastid such as a chloroplast these quinones have various numbers of isoprenoid residues, such as nine for plastoquinone A, the most common plastoquinone in higher plants see above.) The plastoquinones involved in photosynthetic electron transport are divided into two categories (1) the two plastoquinones that rapidly receive single electrons from Peso (Qa and Qb) and (2) a mobile group or pool of about 10 plastoquinones that subsequently receives two electrons (plus two H+ s) from QB (all of these quinones occur in the lamellar membranes see Table 5-3). From the plastoquinone pool, electrons move to the cytochrome b f complex. 

Indole alkaloids are derived from tr)y)tophan, which is formed in the shiki-mate pathway. In the case of the terpenoid indoles, tryptophan is usually first converted to tiyptamine by the enzyme tryptophan decarboxylase (TDC) (Fig. 2.9). This enz)une occurs in the cytosol and has been detected in all parts of the developing seedling and in cell cultures of C. roseus (De Luca, 1993). If appears to be a pyridoxoquinoprotein, as two molecules of pyridoxal phosphafe and two molecules of covalently bound pyrroloquinoline quinone were found per enz)une molecule (Pennings et al, 1989). A tdc cDNA clone has been isolafed by immunoscreening of a C. roseus cDNA expression library (De... 

Several important groups of plant compounds, including cytokinins, chlorophylls and the quinone-based electron carriers (the plastoquinones and ubiquinones), have terpenoid side chains attached to a non-terpenoid nucleus. These side chains facilitate anchoring to or movement within membranes. In the past decade, proteins have also been found to have terpenoid side chains attached. In fact, all eukaryotic cells appear to contain proteins that have been post-translationally modified by the attachment of C15 and C20 terpenoid side chains via a thioether linkage. 

One of the identified stimulators was the terpenoid strigol 31 (Scheme 1.9). In attempts to develop an efficient tool to eradicate the witchweed (by artificially provoking its growth prior to the growth of com), numerous efforts were dedicated to the synthesis of 31 and its analogs. Later studies disclosed the presence of another active compound in the exudate of Sorghum, the substituted hydroquinone 32. As is typical for hydroquinone derivatives, 32 was found to be quite amenable to oxidation to quinone 33, which occurs readily in the soil. 

Tobacco leaf has a complicated chemical composition including a variety of polymers and small molecules. The small molecules from tobacco belong to numerous classes of compounds such as hydrocarbons, terpenes, alcohols, phenols, acids, aldehydes, ketones, quinones, esters, nitriles, sulfur compounds, carbohydrates, amino acids, alkaloids, sterols, isoprenoids [48], Amadori compounds, etc. Some of these compounds were studied by pyrolysis techniques. One example of pyrolytic study is that of cuticular wax of tobacco leaf (green and aged), which was studied by Py-GC/MS [49]. By pyrolysis, some portion of cuticular wax may remain undecomposed. The undecomposed waxes consist of eicosyl tetradecanoate, docosyl octadecanoate, etc. The molecules detected in the wax pyrolysates include hydrocarbons (Cz to C34 with a maximum of occurrence of iso-Czi, normal C31 and anti-iso-C32), alcohols (docosanol, eicosanol), acids (hexadecanoic, hexadecenoic, octadecanoic, etc ). The cuticular wax also contains terpenoids such as a- and p-8,13-duvatriene-1,3-diols. By pyrolysis, some of these compounds are not decomposed and others generate closely related products such as seco-cembranoids (5-isopropyl-8,12-dimethyl-3E,8E,12E,14-pentadecatrien-2-one, 3,7,13-trimethyl-10-isopropyl-2,6,11,13-tetradecatrien-1al) and manols. By pyrolysis, c/s-abienol, (12-Z)- -12,14-dien-8a-ol, generates mainly frans-neo-abienol. 

From the viewpoint of organic synthesis, nature provides us with a number of target molecules, which have novel structures and a variety of biological activities. As already shown in Section II.A, electrochemical oxidation of phenols has been applied successfully to natural products synthesis. Hypervalent (diacyloxyiodo)benzenes have also been proved to be effective for natural products synthesis. Generally, oxidation of o- and p-methoxyphenols in MeOH provides the corresponding o- and p-quinone monoketals, respectively. They are utilized as promising synthons for natural products and related bioactive compounds, as demonstrated by Swenton . Recently, these quinone monoketals have been utilized for syntheses of terpenoids, neolignans, anthraquinones, alkaloids and related compounds. 

Several representative classes of compounds have been isolated from Polygonum species of plants, including quinone, phenol, stilbene, tannin, terpenoid, flavonoid and catechol compounds. The structures of some of the common compounds occuring in Polygonum are given below. 

Griffiths, W.T., D.R. Trelfall, and T.W. Goodwin Observations on the nature and biosynthesis of terpenoid quinones and related compounds in tobacco shoots Europ. J. Biochem. 5 (1968) 124—132. 

Interest in enzyme stereospecificity and the stereochemistry of prochiral centres, such as the methylene groups of mevalonic acid, has necessitated more precise definitions of the stereochemistry of the various molecules involved and of the enzymological consequences. The use of multiply labelled mevalonic acid in terpenoid and steroid biosynthesis has been reviewed by Hanson. The Proceedings of the 1970 Phytochemical Society symposium have been published. They include a general discussion of terpenoid pathways of biosynthesis by Clayton and specific chapters on monoterpenoids, diterpenoids, eedysones, carotenoids, isoprenoid quinones, and chromanols. Other reviews concerning biosynthesis have appeared on furanocoumarins, indole alkaloids, monoterpenoids, and diterpenoids. ... 

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