3,5,7,4’-Flavone Flavonoid complex

Several complexes of [Bu2Sn(IV)] with flavonoid glycosides 3-[6-0-(6-deoxy-a-L-mannopyranosyl)-(jS-D-glucopyranosyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-H-l-benzopyran-4-one (rutin) and 2, 4, 3-trihydroxy-5, 4-dimetoxychalcone 4-rutinoside (hesperidin) and flavonoid aglycones (quercetin, morin, hesperitin, and other flavones) (Figure 5) were prepared. 

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. 

Flavonoids are a complex group of polyphenolic compounds with a basic C6-C3-C6 structure that can be divided in different groups flavonols, flavones, flavanols (or flavan-3-ols), flavanones, anthocyanidins, and isoflavones. More than 6,000 flavonoids are known the most widespread are flavonols, such as quercetin flavones, such as lu-teolin and flavanols (flavan-3-ols), such as catechin. Anthocyanidins are also bioactive flavonoids they are water-soluble vegetable pigments found especially in berries and other red-blue fruits and vegetables. 

Flavanone 3 -hydroxylase (F3 H ECl.14.13.21 CYP75B) activity was initially identified in microsomal preparations of golden weed (Haplopappus gracilis) [110]. E3 H from irradiated parsley cell cultures was later biochemically analyzed and characterized as a cytochrome P450 having an absolute requirement for NADPH and molecular oxygen as cofactors [111]. The enzyme has been shown to have activity with flavanones, flavones, dihydroflavonols, and flavonols, but does not appear to have activity with anthocyanidins [111]. The first cDNA clone for E3 H was isolated from Petunia [112]. It has been suggested that E3 H may serve as an anchor for the proposed flavonoid multi-enzyme complex on the cytosolic surface of the endoplasmic reticulum [44]. 

The farinose exudate of the frond of the fern Pityrogramma calomelanos (Adiantaceae) has been the source of complex flavonoids characterized by a novel Ce-Cs-Ce-Cs-Ce skeleton (Table 15.7). This group includes four flavanones, calomelanols G (238), H (239), I (240), and J (241) (Figure 15.10). In these compounds, a molecule of p-coumaric or cinnamic acid appears to be fused with the A-ring of the flavanone. Biosynthetic pathways for these complex flavanones and related flavones, chalcones, and dihydrochalcones in P. calomelanos and other Pityrogramma species have been proposed by the authors. 

Studies have shown that quercetin, kaempferol, and fisetin inhibited transcription with RNA polymerase II in permeabilized normal human fibroblasts (WI-38 cells) flavone and chrysin exhibited weak activity. Addition of quercetin to an ongoing transcription reaction arrested it promptly, suggesting that quercetin was inhibiting the elongation step. The effects of several flavonoids (quercetin, quercetagetin, myricetin, and baicalein) exhibited complex interactions with DNA and RNA polymerases, depending on the particular flavonoid and the enzyme species. 

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