Quercetin chemical structure

Chemical structures of reported inhibitors of HIV-1 integrase. (I) aurintricarboxylic acid monomer (II) cosalane (III) dihydronaphthoquinone or DHNQ (IV) primaquine (V) caffeic acid phenethyl ester or CAPE (VI) quercetin (VII) quercetagetin (VIII) AG1717 (IX) 3-conidendrol (X) suramin (XI) curcumin. 

As previously mentioned, certain flavonoids can penetrate into the hydrophobic core of membranes, a feature that mainly relies on their hydrophobic character, which is dictated by flavanoid chemical structure and spatial conformation. When flavonoid hydrophobicity was assessed from the partition coefficient between ra-octanol and an aqueous solution, the following order of hydrophobicity was observed flavone, genistein > eriodictyol, myricetin, quercetin, kaempferol, hesperetin, daidzein > > galangin, morin, flavanone, naringenin, taxifolin (Table 4.1). 

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). 

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 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).

FIGURE 8.4 Chemical structures of kaempferol, quercetin, and isorhamnetin. 

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. 

Figure 1, Chemical structure of quercetin, wogonin and oroxylin A.

The first chemical constituent was isolated from podophyllin in 1880 and named podophyllotoxin (97). A structure was proposed in 1932 and after some fine-tuning (98) was shown to be the lignan (60). As might be expected, the crude resin contains a variety of chemical types, including the flavonols quercetin and kaempferol (99). Although these other constituents undoubtedly have biological activity, it is the lignans that have received most attention and to which we shall devote the remainder of this section. 

Flavonoids can interact with 02 in two different ways they can combine chemically with 02 or they can transfer the excitation energy of 02 to the flavonoid molecule, which then enters an excited state. The latter phenomenon is called quenching [35]. Flavonoids have been reported to quench singlet oxygen [17, 135-137], but only Toumaire et al. tried to establish a structure-activity relationship [17]. Sorata et al. studied the suppression of photosensitized hemolysis of human erythrocytes by the flavonols quercetin and rutin [135]. At lower concentrations, the effect of quercetin was more important than that of rutin [135]. According to Takahama et al., quercetin suppressed >02-dependent photobleaching of... 

Flavones have a main structural fingerprint, which is the presence of a double bond between carbons 2 and 3 of the central ring From all the possible chemically derived products of the basic structure, those with a C3 hydroxylation pattern are specifically referred to as flavonols. This group constitutes a special type of flavones including some widespread compounds such as quercetin. 

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