Flavonols compounds

Flavones and Flavonols Compound Subst. Compound Subst. 

Fiussello, N., Morino, D., Bona, G. 1979. Effect of environmental factors on flavonol compounds of Betula alba. Allionia 23 103-108. 

In the Ames test for mutagenicity, ethanol extracts of arnica produced a two- to fourfold increase in the number of rever-tants, as compared to controls with S. typhimurium TA98 with and without metabolic activation and with S. typhimurium TAIOO with metabolic activation an increase was not seen with TAIOO without metabolic activation (Goggelmann and Schimmer 1986). The authors indicated that the effect was likely due to the flavonol compounds in arnica, noting that "the origin of the plant is important for the presence of essential components" and that results can differ based on the district of growth and the preparation of the extract (Goggelmann and Schimmer 1986). 

Flavonol compounds isolated from sweet wormwood were found to potentiate the activity of berberine and norfloxacin against a multidrug-resistant strain of Staphylococcus aureus (Stermitz et al. 2002). 

Structure information on the flavonol compounds (Table 18.1), which includes the type of aglycone, the attachment points of the substituents to the aglycone, the sequence of the glycan part, and the interglycosidic linkages, could be obtained from the MS/MS spectra. The results of our experiments combined with publication data (Cuyckens and Claeys, 2005 Ferreres et al., 2004 Cuyckens et al., 2001) were applied to establish the systematic identification method for flavonol constituents. 

Examples of flavonol compounds encountered in dyes include quercetin and rutin, while the flavones include apigenin and luteolin. 

Morin is 2-(2,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-l-benzopyran-4-one (also, 2, 3,4, 5,7-pentahydroxyflavone) it is a flavonoid (flavonol) compound and is the principal component of so-called old fustic , a dye derived from Madura tinctoria (L.) Steudel (Moraceae formerly Chlorophora tinctoria (L.) Gaud.) (Schweppe, 1992 Merck Index, 1996). Use of old fustic in pigments has been mentioned by Harley (1982). Morin is hsted in the Colour Index as Cl 75660/Natural YeUow 8 and 11. 

In the example below, Bhardwaj and coworkers synthesized tetramethoxyflavone 36 this flavonol was believed to be the structure of a compound isolated from Artemisia annua Methyl ketone 37 and aldehyde 38 were smoothly condensed to afford chalcone 39 in 73% yield. 39 was then converted to 40 under slightly modified AFO conditions in low yield. Selective demethylation of 40 gave 36. However, spectral data and melting point data of 36 did not match up with the compound isolated from the plant. Hence, the original structure was misassigned and was not flavonol 36. 

In addition, Pfister and coworkers investigated 3-hydroxyflavone-6-carboxylic acids as histamine induced gastric secretion inhibitors. After condensing 3-acetyl-4-hydroxybenzoic acid (45) with a variety of aldehydes 46 to deliver the chalcones 47, these purified chalcones were then subjected to the standard AFO conditions to afford flavonols 48 in 51-80% yield. Subsequent alkylation of 48 with methyl iodide or isopropyl iodide followed by saponification of the corresponding esters gave the target compounds. 

A detailed study of the flavonoid chemistry of the island endemics, the closely related G. tinctoria, and live additional species from the mainland provided additional evidence pointing toward G. tinctoria as the ancestral species (Pacheco et al., 1993). The flavonoid profiles of all species consisted of flavonol glycosides as major components with an unidentified flavone glycoside and several unidentified phenolic compounds (presumably not flavonoids). The pattern of distribution of the flavonol glycosides and unidentified flavones within the set of nine species proved to be extremely informative. (The phenols were ubiquitous and are not considered further.) Kaempferol glycosides were seen in neither the island species nor G. tinctoria, but were present, in several combinations, in the rest of the mainland taxa. The isorhamnetin glycosides showed the reverse pattern, with one exception the island endemics and G. tinctoria exhibited these compounds, whereas four of the other mainland species did not. The sole exception is G. boliviari, which exhibited one of the isorhamnetin derivatives. 

Fig. 6.14 Compound 565, the flavonol triglycosides from Ranunculus species on the Kerguelen Islands...

Three distinct chemotypes were observed. Taxa from each of the three areas noted above exhibited unique combinations of the compounds and compound types, although there was a degree of variation within most groups, as one might expect. The North American chemotype was characterized by very high frequency of the sulfated cinnamic-acid derivatives, a frequency of flavonol derivatives of... 

As relatively few standard compounds are available from commercial or other sources, identification of flavonol glycosides has to be achieved by alternative means, for example UV-, H- and C-NMR spectroscopy. Therefore hydrolysing all glycosides to aglycones followed by HPLC determination offers a practical method for the quantitative determination of flavonoids in tea (Hertog et al, 1993a Wang and Helliwell, 2001). 

Tea flavonoids, or tea extracts, have been linked to benefits in reducing the risk of certain cancers and cardiovascular diseases in experimental animals. However, epidemiological studies have produced inconsistent evidence in the relationship between tea drinking and cancer (Blot et a/., 1997 Goldbohm etal, 1996 Hertog eta/., 1997 Yang eta/., 1996). Therefore, further research is needed before definitive conclusions on the impact of tea consumption upon the cancer risk in humans can be reached. The metabolites of catechins and flavonols after consumption of tea infusions have scarcely been investigated, and thus more research is needed as to the role of those compounds in the reported health benefits of tea consumption. 

Havonoids are made up of a number of classes of very similar groups in which two phenyl rings are connected by a three-carbon unit [10], The open structure members are yellow in color and termed as chalcones, and simple cyclization to a furanoid structure deepens the color to the orange aurones. The most usual flavonoids are, however, the pale-yellow flavones and flavonols, or 3-hydroxyflavones, which will be treated here, and the red-blue anthocyanins, which will be treated in the next section. Figure 13.4 shows examples of these main classes and their structural relationships. The natural compounds of all classes often occur as glycosides and as methyl ethers. 

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