Flavonoid subclasses

Figure 5.4. Abbreviated scheme for biosynthesis of major flavonoid subclasses, showing the primary enzymes and substrates leading to different subclasses. Bold-faced, uppercase abbreviations refer to enzyme names, whereas substrate names are presented in lowercase letters. PAL, phenylalanine ammonia lyase C4H, cinnamate 4-hydroxylase 4CL, 4-coumarate CoA ligase CHS, chalcone synthase CHI, chalcone isomerase CHR, chalcone reductase IPS, isoflavone synthase F3H, flavonone 3-hydroxylase F3 H, flavonoid 3 -hydroxylase F3 5 H, flavonoid 3 5 -hydroxylase FNSI/II, flavone synthase DFR, dihydroflavonol 4-reductase FLS, flavonol synthase ANS, anthocyanidin synthase LAR, leucoanthocyanidin reductase ANR, anthocyanidin reductase UFGT, UDP-glucose flavonoid 3-O-glucosyltransferase. R3 = H or OH. R5 = H or OH. Glc = glucose. Please refer to text for more information.

To ensure coverage of a broad spectrum of journals containing both original and review articles, bibliography databases, such as CAB abstracts, BIDS ISI and Embase, Medline and Current Contents Agriculture and Food Citation index, were searched. Terms used for all database searches were kept simple to limit the risk of missing any original publications (Table 4.5). Initially, each flavonoid subclass was entered and then cross-searched with the... 

Walle T. 2007. Methoxylated flavones, a superior cancer chemopreventive flavonoid subclass Semin Cancer Biol 17 354-362. 

Flavonoids constitute a large class of polyphenols found in fruits and vegetables that share a common skeleton of phenylchromane. This basic structure allows a large number of substitution patterns leading to several subclasses of flavonoids, such as flavonols, flavones, flavanones, flavanols, anthocyanidins, isoflavones, dihydroflavonols, and chalcones. Among the diverse flavonoid subclasses, flavonols (especially quercetin) and flavanols (catechins) are the most abundant in our food. Flavonols are present in foods as diverse glycosides, whereas flavanols are usually found as aglycones. 

Recently performed studies on structure-activity relationships for inhibition of BCRP by flavonoids showed that the presence of the 2,3-double bond in ring C, ring B attached at position 2, an OH group at position 5, lack of hydroxylation at position 3, and hydrophobic groups substituted at positions 6, 7, 8, or 4 are favorable for BCRP modulation [239]. The studies were carried out with five flavonoid subclasses flavones, isoflavones, flavanones, flavonols, and chalcones (Figs. 2 and 6). For several compounds the 50% in-... 

Figure 2.2 Flavonoid subclasses and names of prominent food flavonoids.

The data are presented in different tables according to the main subclasses of flavonoids. Tables are divided in four columns that include the flavonoid subclass substituent, its trivial name, the type of tumor cell line inhibited and the reference. Cytotoxic values are not presented because the authors use different protocols and different times of incubation of flavonoids with cancer cells and the results would not be comparable. The order of each flavonoid in a Table is based firstly in the number of substituents, then in their position and finally in the type of substituent. Sometimes, the structure of a flavonoid does not appear in the tables, generally because it has a complicated structure. In such cases, you can find it in the reference or in the NCI database, using the NSC-number (http //dtp.nci.nih.gov/). 

Differences between flavonoid subclasses flavonols have a 2-3 double bond, 3-hydroxyl and 4-ketone group flavones have a 2-3 double bond and 4-ketone group flavanones have a 4-ketone group isoflavones have a 4-ketone group and have the B ring attached at the 3-position flavan-3-ols are hydroxylated or gaUoylated at the 3-position. 

Flavonoid subclass Dietary flavonoids Some common food sources... 

Fig. 69.1 Skeleton of a C6-C3-C6 defining the ilavraioid class and stractures of the main flavonoid subclasses...

Food Flavonoid subclass Extraction Stationary phase Mobile phase Detector(s) References... 

Fig. 74.3 The generic three ring (A, B, and C) carbon backbone structures (C6-C3-C6) of the major flavonoid subclasses found in food [17]...

Chemical Structure of the Main Flavonoid Subclasses and Some of Their More Representative Components Together with Their Spectral Characteristics Recorded Online after Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC) Separation Using Methanol-Water Acidified with Sodium Phosphate (pH 3.3) ... 

Table 2 Estimated dietary intake of flavonoid subclasses in different countries...

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