Flavonoid skeleton

Figure 5.1. The basic C6-C3-C6 flavonoid skeleton (upper panel) and typical flavonoid subgroups (lower panel). The biosynthetic origins of carbon atoms and standard numbering are also illustrated in the upper panel.

The SMER, Fig. (27), is similar model to estrogen receptor excluded volume (RExV) postulated by Kym et al. [212]. The volume of die SMER was 424.7 A3. Most flavonoid skeletons (A-C rings) lay into die SMER, however, the prenyl (geranyl) groups existed out of die SMER as shown in Fig. (27). 

The main flavonoid skeleton derives from the stepwise condensation of three molecules of malonyl CoA with one molecule of 4-coumaroyl CoA, a reaction catalyzed by chalcone synthase (CHS) to form naringenin (2, 4,4 ,6,-tetrahydroxy) chalcone, the common intermediate in the formation of all flavonoids with 5,7-dihydroxy (flavone numbering) A-ring substitution. In some plants, however, an NADP-dependent chalcone-ketide reductase coacts with CHS to form 6 -deoxychalcone, the precursor of 5-deoxyflavonoids. The resulting chalcones undergoe a stereospecific cyclization to the corresponding (2S) flavanones, the... 

The flavonoid skeleton present in flavonolignans can be readily identified from their NMR spectra. Silybin (1) and its congeners, practically all of which bear a 3,5,7-trihydroxy-3, 4 -dioxygenated dUiydroflavone moiety, exhibit signals for... 

A large number of phenolics are derived from the C15 flavonoid skeleton, which is synthesised via the chalcone synthase (CHS) catalysed condensation of p-coumaroyl-coenzyme A and three molecules of malonyl-CoA. In most plant families, the initial CHS product is a tetrahydroxychalcone, which is further converted to other flavonoid classes, such as flavones, flavonols, flavanones, flavan-3-ols, isoflavones and anthocyanins (Fig. 2). Structural diversity among the phenylpropanoids arises from a variety of modifications, including... 

Wine tannins are polyphenolic compounds extracted from the skins and seeds of grapes during the process of wine-making. These phenolic compounds exhibit a wide diversity of structures having a flavonoid skeleton (Figure 6.1). 

Flavanone 3P-hydroxylase (F3H) converts the basic flavonoid skeleton flavanone to dihy-droflavonol through hydroxylation at the 3-posi-tion [77], a critical early step in anthocyanin flower pigment biosynthesis. Flavonol synthase (FLS) is a 2-ODD that catalyzes the formation of a double bond between C-2 and C-3 in dihy-droflavonols [78]. Flavonol 6-hydroxylase (F6H) is also a 2-ODD [79]. 

Fig.1 The basic C6-C3-C6 flavonoid skeleton and examples of common glycosylated flavonoids that are found in foods...

Fig. 1. Numbering of flavonoids skeleton used in MOP AC and NODANGLE calculations and angles used in the interpretations. The angle subscript indicates the ring number.

The main subclasses of flavonoids are the flavones, flavonols, flavan-3-ols, isoflavones, flavanones and anthocyanidins (Figure 1.1). Other flavonoid groups, which quantitatively are in comparison minor components of the diet, are dihydroflavonols, flavan-3,4-diols, coumarins, chalcones, dihydrochalcones and aurones (Figure 1.2). The basic flavonoid skeleton can have numerous substituents. Hydroxyl groups are usually present at the 4, 5 and 7 positions. Sugars are very common with the majority of flavonoids existing... 

Figure 8.2 Numbering of the C6-C3-C6 flavonoid skeleton and the chemical structures of the main subclasses of flavonoids and isoflavonoids present in the diet.

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