Flavonoids classes

The chromatographic conditions as mentioned above must in most cases be adapted to the matrix under study, i.e., to the predominant flavonoid classes. Paganga et al. studied aglycone flavonoids in apples, onions, and tomatoes, and were able to develop another solvent gradient enabling very good separation of the different aglycones (Table 2.3.2). 

Lagiou, P. et al.. Intake of specific flavonoid classes and coronary heart diseased a case-control study in Greece, Eur. J. Clin. Nutr., 58, 1643, 2004. 

As with other flavonoid classes, the anthocyanins generally occur in higher plants [11,12]. Their presence is immediately apparent as a result of their color, and this is readily conhrmed by treating a small piece of tissue with acidic methanol, and thus many red fruits and some flowers of red-blue shades are suitable sources of anthocyanins. 

Flavanones are 2,3-dihydroderivatives of flavones which have a saturated C-ring, and are mainly present in their glycosidic forms. In contrast to other flavonoid classes found in a wide range of foods and plants, flavanones are present mainly in citrus fruit and in some aromatic herbs such as ntint. However, reports on the isolation of antinticrobial flavanones from medicinal plants mainly concerned those belonging to the Leguntinoseae family. 

Assigned H and C chemical shifts characteristic for the various flavonoid classes are shown in Table 2.1-Table to 2.6. The names of the flavonoids listed in Table 2.1-Table 2.6 are given in Table 2.7. The structures of the flavonoids listed in Table 2.1-Table 2.7 are shown in Figure 2.8-Figure 2.16. 

The application of standardized UV (or UV-Vis) spectroscopy has for years been used in analyses of flavonoids. These polyphenolic compounds reveal two characteristic UV absorption bands with maxima in the 240 to 285 and 300 to 550 nm range. The various flavonoid classes can be recognized by their UV spectra, and UV-spectral characteristics of individual flavonoids including the effects of the number of aglycone hydroxyl groups, glycosidic substitution pattern, and nature of aromatic acyl groups have been reviewed in several excellent books. ... 

Study Flavonoid Class Follow-up (Years) No. of Cases RR (95% Cl) Ref. 5 ... 

FIGURE 9.1 The main flavonoid classes and examples of common dietary flavonoids. 

In three of the volumes of The Flavonoids, Advances in Research, published between 1975 and 1993, flavanones and dihydroflavonols were part of the chapter on Minor Flavonoids, expertly written by Professor Bruce Bohm. These Minor Flavonoid chapters also included chalcones, dihydrochalcones, and aurones. The term Minor Flavonoids was first used by Harborne in 1967 to encompass not only flavanones, chalcones, and aurones, but also isoflavonoids, biflavonyls, and leucoanthocyanidins, because so few compounds belonging to each of these flavonoid classes were known at that time. For example, only about 30 flavanone and dihydroflavonol aglycones, 19 chalcones, and 7 aurones were known in 1967. The number of known minor flavonoids increased considerably in the next two decades, so that when the checklist for The Flavonoids, Advances in Research Since 1980 was published in 1988, 429 known flavanones and dihydroflavonols (including glycosides) were listed, 268 chalcones and dihydrochalcones, and 29 aurones. In the last 15 years, the total number of known compounds in these flavonoid classes has more than doubled, so that the term minor flavonoids is no longer appropriate. Consequently, it has been decided that separate chapters should be devoted to the flavanones and dihydroflavonols (this chapter), and chalcones, dihydrochalcones, and aurones (Chapter 16). 

Whilst the updating aspect of the chapters is seen as the prime contribution of this book, an effort also has been made to include a summary of previous knowledge in the field to enable the reader to place new advances in this context. Chapters 1 and 2 review the application of contemporary isolation, quantification, and spectroscopic techniques in flavonoid analysis, while Chapter 3 is devoted to molecular biology and biotechnology of flavonoid biosynthesis. Individual chapters address the flavonoids in food (Chapter 4) and wine (Chapter 5), and the impact of flavonoids and other phenolics on human health (Chapter 6 and, in part, Chapter 16). Chapter 8 reviews newly discovered flavonoid functions in plants, while Chapter 9 is the first review of flavonoid-protein interactions. Chapters 10 to 17 discuss the chemistry and distribution of the various flavonoid classes including new structures reported during 1993 to 2004. A complete listing of all known flavonoids within the various flavonoid classes are found in these later chapters and the Appendix, and to date a total of above 8150 different flavonoids has been reported. 

A huge compilation of13 C NMR data on various flavonoid classes. Data on anthocyanins are very limited, and several assignment mistakes appear throughout the book. 

The structural diversity of metabolites belonging to the different flavonoid classes, including their oxygenation patterns, glycosylation, sulfation, acylation, methylation, and/or prenylation are best illustrated in a recent text,9 as well as in several earlier monographs.10 14 These different substitution reactions, which are catalyzed by substrate-specific and position-oriented enzymes, contribute to the enormous diversity of flavonoid compounds that amount to >5000 chemical structures in Nature and hence, to the wide spectrum of functional roles they play in... 

Cytochrome P450 monooxygenases play two important roles in flavonoid biosynthesis. One involves the modification of ring C of flavanones, where they attack nonphenolic carbon atoms, thus resulting in the creation of new flavonoid classes such as flavones, flavonols, and isoflavonoids. The other involves the introduction of new hydroxyl groups on phenolic rings A and B, thus increasing the... 

Whereas some flavonoids may lack one or more hydroxyl groups from the usual 5,7,4 -oxygenation pattern of naringenin, others may acquire new hydroxyls through the action of some of the hydroxylases mentioned above. These commonly occur at positions 6, 8, 2, 3, and/or 5 and may be fiirther substituted. On the other hand, 2-hydroxylated flavonoids are of rare occurrence. The following examples chosen from the different flavonoid classes demonstrate both phenomena, although... 

Although relatively small in number, these compounds are characterized by a high level of prenylation, including four di-, four tri-, and one tetraprenyl derivatives, and a low level of O-methylation with only two 2 -0-methylated compounds.149 Whether enzymic prenylation occurs prior to, or after, assembly of the diphenylpropane structure has yet to be determined. Examples of the diversity of prenylation among different flavonoid classes are shown in (26-33). 

Within each flavonoid class, further diversity results from modifications of their three ring skeleton, including... 

The rich red color of strawberries comes from numerous phytochemicals of the polyphenol family and its major subgroup, flavonoids, which are densely found in strawberries. One flavonoid class in particular, antho-cyanins, accounts for most of the red pigmentation of strawberries, but also present are ellagic acid, ellagitannins, catechins, and cinnamic acid, each having significant health research interest. In preliminary laboratory tests, these strawberry polyphenols are showing evidence that they may lower the risk of inflammation, cancer, and cardiovascular diseases. 

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