Anthocyanins and Flavones

In the living cell these compounds exist in more complex bound forms, interacting with other molecules, for example flavones, and the actual observed colour depends on these interactions. However, it is interesting that even in vitro, simple pH changes bring about extreme changes in the electronic absorption of these molecules. For example cyanidin is red in acidic solution, violet at intermediate pH and blue in weakly alkaline solution, the deep colours being the result of extensive resonance delocalisation in each of the structures. 

The naturally occurring llavones are yellow and are very widely distributed in plants. They accumulate in almost any part of a plant, from the roots to the flower petals. Unlike the anthocyanins, which are too reactive and short-lived, the much more stable llavones have, from time immemorial, been used as dyes, for they impart various shades of yellow to wool. As an example, the inner bark of one of the North American oaks, Quercus velutina, was a commercial material known as quercitron bark and much used in dyeing it contains quercetrin. The corresponding aglycone, quercetin, is one of the most widely occurring flavones, found, for example, in Chrysanthemum and Rhododendron species, horse chestnuts, lemons, onions and hops. 

Coumarin has the sweet scent of newly mown hay, and is used in perfumes. The official birthdate of the synthetic fragrance industry is held to be the discovery of a synthetic route to coumarin by W. H. Perkin in 1868 using the reaction we now call the Perkin condensation (12.3.2.2). 

Kobayashi, J., Cheng, J., Nakamura, H., Ohizumi, Y., Hirata, Y., Sasaki, T, Ohta, T. and Nozoe, S. Tetrahedron Lett., 1988, 29, 1177. 

Toyama-Kato, Y. and Yoshida, K., Tetrahedron Lett, 2005, 46, 6645. 

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The purpose of this chapter is to provide an overview of our present knowledge about the health benehts of pigments, particularly their effects on chronic diseases. We examine the effects of lipophilic (carotenoids, chlorophylls) and hydrophilic pigments (anthocyanins and flavones-flavonols), and curcumin. Descriptive and mechanistic studies are reviewed in regard to common chronic diseases. 

Anthocyanins are colored flavonoids that attract animals when a flower is ready for pollination or a fruit is ready to eat. They are glycosides (i.e., the molecule contains a sugar) that range in color from red, pink, and purple to blue depending on the number and placement of substitutes on the B ring (see Fig. 3.7), the presence of acid residues, and the pH of the cell vacuole where they are stored. Without the sugar these molecules are called anthocyanidins. The color of some pigments results from a complex of different anthocyanin and flavone molecules with metal ions. 

The role of anthocyanins and flavones in providing stable blue flower colors in the angiosperms has more recently been outlined by Harborne and Williams." It was apparent... 

The antioxidative role of anthocyanins and flavones in providing stable blue flower colors in the angiosperms has been studied. The leaf anthocyanins and flavones showed a protective effect against UV-B radiation. These protective UV-B flavonoids in angiosperms were mainly kaempferol (9), quercetin (10), cyanidin (51), luteolin (65), and isoorientin C-glycoside (flavone C-glycoside, 66) (Fig. 14) [35]. 

The term pseudo-base has been used less widely and less consistently than pseudo-acid. Logically it should be applied to a species which undergoes a change of structure when it adds on a proton. This would include the anions of the pseudo-acids discussed above, and a few uncharged species such as coloring matters (e.g., anthocyanins and flavones) derived from 7-pyrone, where the addition of a proton involves the reaction... 

Kosaku Tadeka and his coworkers achieved major new results in exploring the structure of the cornflower dye (called protocyanin complex) in 2005 four metal ions (one iron, one magnesium, and two calcium ions) were shown to form a complex with 6-6 molecules of other anthocyanin and flavone pigments. In the vacuoles of rose petals, no metals were found. 

Anthocyanins and flavones Fruit (TFA, phosphoric acid) with organic 280, 320, 370, 77... 

On the other hand, all the biosynthetic methods, in their broad sense, used by insects, discussed in this book, are available to plants. That is, the formation of fatty acids and their derivatives, such as hydrocarbons the acetogenins and especially the terpenes and aromatic compounds are all used by plants. Acetogenins are not as prominent among plant products as the others, except in the formation of anthocyanins and flavones. Only special areas are left to insects alone. It is surprising, as more information accumulates, how insects and plants seem often to have found similar or the same way to biosynthesize certain compounds. Some authors call this parallel evolution. 

This chapter, therefore, aims to present a brief unified summary of general techniques, with reference to the different categories of structure flavones and flavonols (and their glycosides), isoflavones, flavanones, chalcones, anthocyanins, and proanthocyanidins. 

There are many branches to the flavonoid biosynthetic pathways, with the best characterized being those leading to the colored anthocyanins and proanthocyanidins (PAs) and the generally colorless flavones, flavonols, and isoflavonoids. Genes or cDNAs have now been identified for all the core steps leading to anthocyanin, flavone, and flavonol formation, as well as many steps of the isoflavonoid branch, allowing extensive analysis of the encoded enzymes (Table 3.1). In addition, several DNA sequences are available for the modification enzymes that produce the variety of structures known within each class of compound. 

The key enzymes involved in the formation of the hydroxycinnamic acids (HCAs) from phenylalanine and malonyl-CoA are now discussed in detail, while later sections address the branches of the flavonoid pathway leading to anthocyanins, aurones, flavones, flavonols, PAs, and isotlavonoids. This is followed by brief reviews of the regulation of flavonoid biosynthesis and the use of flavonoid genes in plant biotechnology. To assist the reader. Figure 3.1 presents the carbon numbering for the various flavonoid types discussed. 

There are few studies on vacuolar importation of flavonoids other than anthocyanins and PAs. Klein et al. reported uptake of flavone glycosides by isolated H. vulgare primary leaf vacuoles via a vacuolar H -ATPase linked mechanism,and by vacuoles from Secale cereale (rye) mesophyll via a possible ABC transporter mechanism. Li et al. "" found medicarpin conjugated to glutathione was also sequestered by an ABC transporter mechanism. 

Approaches to inhibit anthocyanin production that target CHS can cause plant sterility, as flavonols play a role in fertility in some species. It is possible to inhibit anthocyanin production by targeting an enzyme such as DFR, which still allows the formation of flavonols and flavones. Sense or antisense DFR transgenes have been used to reduce or prevent anthocyanin production in several species (Table 3.4), with results similar to those for CHS... 

Two classes of dimeric anthocyanins isolated from plants (section 10.2.6) have been identified in plants for the first time. One class includes pigments where an anthocyanin and a flavone or flavonol are linked to each end of a dicarboxylic acyl unit. The other class includes four different catechins linked covalently to pelargonidin 3-glucoside. During the last decade, seven new desoxyanthocyanidins and a novel type of anthocyanidin called P)Tanoanthocyanidins have been reported (Section 10.2.2). Toward the end of the 20th century, several color-stable 4-substituted anthocyanins, pyranoanthocyanins, were discovered in small amounts in red wine and grape pomace.Recently, similar compounds have been isolated from extracts of petals of Rosa hybrida cv. M me Violet, scales of red onion, and strawberries. About 94% of the new anthocyanins in the period of this review are based on only six anthocyanidins (Table 10.2). 

Tamura, FI. et al.. Structures of a succinyl anthocyanin and a malonyl flavone, two constituents of the complex blue pigment of cornflower Centaurea cyanus. Tetrahedron Lett., 24, 5749, 1983. Sulyok, G. and Laszlo-Bencsik, A., Cyanidin 3-(6-succinyl glucoside)-5-glucoside from flowers of seven Centaurea species. Phytochemistry, 24, 1121, 1985. 

Set detector at 280 nm for catechins (flavan-3-ols), naringin, and benzoic acid derivatives 320 nm for chlorogenic acid, resveratrol, and hydroxycinnamic acids 370 nm for flavones and flavonols and 520 nm for anthocyanins and anthocyanidins (see Table 11.3.1). 

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