Structure of flavonoid

Figure 2 Structures of flavonoids present in root exudates of host plants and inducing nod gene expression in rhizobia (1) as 3,5,7,3 -tetrahydroxy-4 -methoxyflavanone, inducer in Rhizohium legiiminosarum bv. viciae (2) as 3, 4, 5, 7-tetrahydroxy-flavone, inducer in Rhizohium melilotr, (3) as 4, 7-dihydroxyisoflavone, inducer in Bradyrhizohium japonicum (4) as couinestrol, intermediate in phenylpropane metabolism, weak inducer. (From Ref. 64.)...

The ability of flavonoids (quercetin and rutin) to react with superoxide has been shown in both aqueous and aprotic media [59,94]. Then, the inhibitory activity of flavonoids in various enzymatic and nonenzymatic superoxide-producing systems has been studied. It was found that flavonoids may inhibit superoxide production by xanthine oxidase by both the scavenging of superoxide and the inhibition of enzyme activity, with the ratio of these two mechanisms depending on the structures of flavonoids (Table 29.4). As seen from Table 29.4, the data obtained by different authors may significantly differ. For example, in recent work [107] it was found that rutin was ineffective in the inhibition of xanthine oxidase that contradicts the previous results [108,109], The origins of such big differences are unknown. 

FIGURE 29.7 Structures of flavonoids possessing different antioxidant and prooxidant properties. 

FIGURE 1.4 Structures of flavonoids and terpenoids from Gingko biloba. 

Flavonoids are secondary metabolites generally occurring in various plants as glycosides. The chemical structure of flavonoids shows high variety. The basic structure of flavons and flavonols is the 2-phenylbenzo-gamma-pyrone. Flavonoids generally contain two phenol rings linked with a linear three-carbon chain (chalcones) or with three carbon... 

Different MS MS experiments of product ion scan, precursor ion scan, and neutral loss scan modes of selected flavonoids can be carried out in order to confirm the structure of flavonoids previously detected by the full-scan mode. In the product ion scan experiments, MS MS product ions can be produced by CID of selected precursor ions in the collision cell of the triple-quadrupole mass spectrometer (Q2) and mass analyzed using the second analyzer of the instrument (Q3). However, in the precursor ion scan experiments, Q1 scans over all possible precursors of the selected ion in Q3 of the triple quadrupole. Finally, in neutral loss... 

Much data on the structure of flavonoids in crude or semipurified plant extracts have been obtained by HPLC coupled with MS, in order to obtain information on sugar and acyl moieties not revealed by ultraviolet spectrum, without the need to isolate and hydrolyze the compounds. In the last decade, soft ionization MS techniques have been used in this respect, e.g., thermospray (TSP) and atmospheric pressure ionization (API). However, the most used methods for the determination of phenols in crude plant extracts were the coupling of liquid chromatography (LC) and MS with API techniques such as electrospray ionization (ESI) MS and atmospheric pressure chemical ionization (APCI) MS. ESI and APCI are soft ionization techniques that generate mainly protonated molecules for relatively small metabolites such as flavonoids. 

J. Vaya, S. Tamir (2004). The relation between the chemical structure of flavonoids and their estrogen-hke activities. Curr. Med. Chem. 11 1333-1343. 

Fig. (22). Structures of flavonoids 73 - 84 from Glycyrrhiza species and Moraceous plants.

Figure 21.1 Basic Cl 5 (6 3 6) structure of flavonoids and numbering system for carbon positions in the three rings. The B-ring carbon skeleton derives entirely from L-phenylalanine. Ring A and C is originated in the condensation reaction with three malonyl-CoA moieties, B, C. Common patterns of conjugation and substitutions in the B-and C-rings defining the different flavonoid groups.

Fig. 2 Chemical structures of flavonoids (basic types of flavonoids and some selected examples)...

Table 3.1 Chemical Structures of Flavonoids Found in Plants... 

Van Hoorn DEC, Nijveldt RJ, Van Leewen PAM, et al. Accurate prediction of xantine oxidase inhibition based on the structure of flavonoids, EurJ Pharmacol 2002 541 1 I I-I 18. 

The flavonoids, luteolin, luteolin 7-0-/3-d-xyloside and cynaroside, were isolated by El-Moghazi et al. (1979) and orientin and vitexin by Akunzemann and Herrmann (1977). Quercetin-3-glucuronide, rutin, isoorientin, isovitexin and apigenin-7-glucoside have been reported from aniseed (Ozguven, 2000). Figure 18.2 depicts the structure of flavonoids in aniseed. 

Very recently, we reviewed the role of membrane action of flavonoids. The structure of flavonoids enables specific interactions with different membrane proteins (multidrug transporters, voltage-gated and chemically activated ion channels) and also nonspecific interactions with the lipid phase of membranes [8]. 

Chemical structures of flavonoids. These flavonoids consisted of three groups flavone (apigenin and lutolin), flavonols (flavonol, kaempferol, quercetin, myricetin, tangeretin, and nobiletin) and isoflavones (daizein, genistein, biochanin A, and equol). 

Figure 18. Chemical structures of flavonoids according to their hydroxylation.

Fig. (11). Chemical structure of flavonoids isolated from Slachys spruney (family Lamiaceae) quercetin (a) and its glycoside rutin (c), isoscutellarein (b) and its glycoside...

Figure 4. Structure of flavonoid glycosides isolated from Aconitum naviculare (Shrestha et al., 2006).

Fig. (3). Structures of flavonoids that show interference with tubulin polymerization and antimitotic compounds structurally correlated with the former. A Flavone B. C Synthetic chalcones D Combretastatin A-4 E Colchicine.

FIGURE 6.2. Chemical structures of flavonoids and some examples. (Courtesy of Dr. Theeshan Bahorun, University of Mauritius.)... 

Several flavonoids isolated from tea have been analyzed and their structure determined using NMR. There are several problems with the classical methods of analysis of flavonoids in tea. Due to the presence of complex mixtures of flavonoids in tea, they are often characterized as total polyphenols . The colorimetric method for analysis of total phenols can interfere with other reducing compovmds. LC can well resolve peaks for individual flavonoids however, there are only a few standards available commercially, making the assignment of peaks vmcertain in many cases. Thus, the structure of flavonoids giving rise to peaks in LC is often determined using various ID- and 2D-NMR experiments. 

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