Flavonols chemical structure

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... 

Fig. 2.38. Basic chemical structure of flavones, flavonols and flavonoids (chalcones and aurones).

Fig. 2.66. Chemical structures of flavonols in tea. Reprinted with permission from H. Wang et al. [182].

Another isocratic elution method was applied for the determination of flavonols in green and black tea leaves and green tea infusions by RP-HPLC. The chemical structures of the flavonols studied are shown in Fig. 2.66. Infusions of teas were prepared by mixing lg of tea leaves with 100 ml of boiling water for 5min, then they have filtered and used for HPLC analysis. The infusion step was repeated three times. Flavonoids were hydrolysed by mixing lg of tea leaves with 40 ml of 60 per cent aqueous ethanol and 5 ml of 6 M HC1. The suspension was heated at 95°C for 2 h, then filtered and the volume was adjusted to 50 ml with 60 per cent aqueous ethanol. Separation was performed in an ODS column (150 X 4.6mm i.d.) operated at 30°C. The isocratic mobile phase consisted of 30 per cent aqueous ACN in 0.025 M KH2P04, and the pH was adjusted to 2.5 with 6 M HC1. The... 

Phenolic compounds constitute one of the most numerous and widely distributed groups of phytochemicals in the plant kingdom. More than 8000 phenolic compounds have been described and this list continues to expand.49 Phenolic compounds exist as simple molecules, such as the phenolic acids, to highly polymerized structures, such as the proanthocyanidins. Harbome48 classified phenolics into 10 subclasses based upon their chemical structure these subclasses include the simple phenolics, phenolic acids, hydroxycinnamic acids, and flavonoids, among others. The flavonols represent one of the most commonly distributed classes of flavonoid compounds. 

Plant species of the family Apiaceae are known to accumulate flavonoids, mainly in the form of flavones and flavonols (Fig. 21.2). Kreuzaler and Hahlbrock (1973) isolated 24 different flavonoid glycosides from illuminated cell suspension cultures of parsley [P. hortense). The chemical structures of 14 of these compounds were further... 

Figure 4.2 Chemical structures of various flavonoidsThe flavone heterocyclic ring can be reduced or oxidized in various ways. Reduction of the double bond leads to a flavanone. Additional loss of the carbonyl oxygen yields a flavan.Jhe flavone can be hydroxylated to form a flavonol. This can be reduced to a flavanol. The flavan, flavanol, and flavanone each have a chiral center. The biological isomers are not known.

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). 

Flavonol isomers, which differ only in the position of hydroxyl group on their chemical structures, showed different chromatographic behaviors. Liu et al. separated three flavonol isomers (3-hydroxyflavone, 6-hydroxy-flavone, and 7-hydroxyflavone) by a lab-constmcted packed column SFC system with carbon dioxide modified with ethanol containing 0.5% (V/V) phosphoric acid as the mobile phase. The effects of temperature, pressure, composition of mobile phase, and packed-column type on... 

Figure 2 Chemical structures of selected plant polyphenols. Structures include a flavonol (quercetin), isoflavone (daidzein), cinnamic acid (chlorogenic acid), flavan-3-ol (catechin), a lignan microbial metabolite (enterodiol), and a stilbene (resveratrol).

Flavonol isomers, which differ only in the position of hydroxyl group on their chemical structures, showed different chromatographic behaviors. Liu et al. ° separated three flavonol isomers (3-hydroxyflavone, 6-hydro-xyflavone, and 7-hydroxyflavone) by a lab-constructed packed column SFC system with carbon dioxide modified with ethanol containing 0.5% (VAO phosphoric acid as the mobile phase. The effects of temperature, pressure, composition of mobile phase, and packed-column type on the separation were studied. It was indicated that the addition of phosphoric acid to the mobile phase enabled flavonol isomers to be eluted from the column. It was also shown that a phenyl-bonded silica column was better and the ODS column was not as effective for the isomer separation. Increasing pressure shortened the retention time of each compound, with good resolution, and higher temperature led to longer retention times, and even the loss of the bioactivities of these components. Under selected conditions, the separation of these isomers was very satisfactory, as illustrated in Fig. 2. 

The most important members of the flavonoid family include anthocyanidins (e.g., cyanidin, delphinidin, malvidin), flavonols (e.g., quercetin, kaempferol), flavones (e.g., luteolin, apigenin), flavanones (e.g., myricetin, naringin, hesperetin, naringenin), flavan-3-ols (e.g., catechin, epicatechin, gallocatechin) and, although sometimes classified separately, the isoflavones (e.g., genistein, daidzein). For chemical structures see Figure 1. All these phytochemical are frequently referred to as bioflavonoids due to well established effects in human health maintenance. 

Improvements in the instrumentation, ionization sources, high-resolution mass analyzers, and detectors [67-69], in recent years have taken mass spectrometry to a different level of HPLC-MS for natural product analysis. Mass spectrometry detection offers excellent sensitivity and selectivity, combined with the ability to elucidate or confirm chemical structures of flavonoids [70-72]. Both atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) are most commonly used as ionization sources for flavonoid detection [73-76]. Both negative and positive ionization sources are applied. These sources do not produce many fragments, and the subsequent collision-induced dissociation energy can be applied to detect more fragments. Tandem mass spectrometry (MS , n> 2) provides information about the relationship of parent and daughter ions, which enables the confirmation of proposed reaction pathways for firagment ions and is key to identify types of flavonoids (e.g., flavones, flavonols, flavanones, or chalcones) [77-80]. 

Kim, J., Liu, L., Guo, W., and Meydani, M. 2006. Chemical structure of flavonols in relation to modulation of angiogenesis and immune-endothelial cell adhesion. Journal of Nutritional Biochemistry, 17(3), 165-176. 

Certain flavonoids can act as stimnlants or repellents, dependent on the plant or insect species, with some having a dual role (Matsuda, 1978). Feeding choice appears to depend on small differences in chemical structure (Onyilagha et al., 2004) and glycosides, including those of indole and flavonol, may also function as probing stimulants (Kim et al., 1985 Adjei-Afriyie et al, 2000 Takemura et al,... 

Fig. 18.4. Chemical structures of flavonoids Flavanols (Faol), Anthocyanidines (Acn), Flavanones (Faon), Flavones (Fon), Flavonols (Fool), Isoflavones (Ifon, cf. 16.2.9). R H, OH or OCH3...

Fig. 1.2 The chemical structures of flavonoids (a) flavonol, (b) flavone, (c) flavanone, (d) antho-cyanidins and (e) isoflavone...

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