Myricetin from

Zhong, S., Y. Kong, L. Zhou, C. Zhou, X. Zhang, and Y. Wang. 2014. Efficient conversion of myricetin from Ampelopsis grossedentata extracts and its purification by MIP-SPE./. Chromatogr. B 945-946(l) 39-45. 

Effects of Allelochemlcals on ATPases. Several flavonoid compounds inhibit ATPase activity that is associated with mineral absorption. Phloretin and quercetin (100 pM) inhibited the plasma membrane ATPase Isolated from oat roots (33). The naphthoquinone juglone was inhibitory also. However, neither ferulic acid nor salicylic acid inhibited the ATPase. Additional research has shown that even at 10 mM salicylic acid inhibits ATPase activity only 10-15% (49). This lack of activity by salicylic acid was substantiated with the plasma membrane ATPase Isolated from Neurospora crassa (50) however, the flavonols fisetln, morin, myricetin, quercetin, and rutin were inhibitory to the Neurospora ATPase. Flavonoids inhibited the transport ATPases of several animal systems also (51-53). Thus, it appears that flavonoids but not phenolic acids might affect mineral transport by inhibiting ATPase enzymes. 

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

Numerous studies were dedicated to the effects of flavonoids on microsomal and mitochondrial lipid peroxidation. Kaempferol, quercetin, 7,8-dihydroxyflavone and D-catechin inhibited lipid peroxidation of light mitochondrial fraction from the rat liver initiated by the xanthine oxidase system [126]. Catechin, rutin, and naringin inhibited microsomal lipid peroxidation, xanthine oxidase activity, and DNA cleavage [127]. Myricetin inhibited ferric nitrilotriacetate-induced DNA oxidation and lipid peroxidation in primary rat hepatocyte cultures and activated DNA repair process [128]. 

Although no good quantitative correlation between redox potentials of flavonoids and their prooxidant activities still was not documented, a relationship between the prooxidant toxicity of flavonoids to HL-60 cells and redox potentials apparently takes place [176]. However, there is a simple characteristic of possible prooxidant activity of flavonoids, which increases with an increase in reactive hydroxyl groups in the B ring. From this point of view, the prooxidant activity of flavonoids should increase in the range kaempferol < quercetin < myricetin (Figure 29.7). Thus, for many flavonoids the ratio of their antioxidant and prooxidant activities must depend on the competition between Reactions (14) and (15) and Reaction (17). 

Fig. 2.45. Gradient elution chromatogram of flavonoids investigated. Peak identification 1 = naringin 2 = hesperidin 3 = quercitrin 4 = myricetin 5 = naringenin 6 = hesperetin 7 = luteolin 8 = apigenin 9 = flavone 10 = acacetin. Reprinted with permission from M. A. Hawryt et al. [136].

A new poly(7-oxobomene-5,6-dicarboxylic acid-Wod -norbomene)-coa(cd silica has been synthesized and applied for the separation of flavonoids in model systems and in the extracts of onion, elder flower blossom, lime blossom, St. John s Wort and red wine. Separation was performed in a (150 X 4 mm i.d. particle size 7 /rm) column at room temperature. Flavonoids (quercitrin, myricetin, quercetin, kaempferol and acacetin) were separated with gradient elution water-ACN (20 mmol TFA) from 78 22 to 70 30 v/v in 3min. The flow rate was 2 ml/min. The separation of the standard mixture is shown in Fig. 2.51. It has been stated that the method is rapid, accurate and the MS detection makes possible the reliable identification of flavonoids [153],... 

Fig. 2.51. LC of a flavone standard mixture. For chromatographic conditions see text. Peak identification 1 = quercitrin 2 = myricetin 3 = quercetin 4 = kaempferol 5 = acacetin. Reprinted with permission from C. W. Huck et al. [153].

The flavonoid content of honey has also been frequently investigated by HPLC. Thus, 15 flavonoids were found in the Australian jelly bush honey (Leptospremum polygali-folium), myricetin, luteolin and tricetin being the main constituents. The flavonoid composition of the New Zealand manuka (Leptospermum scoparium) honey differed markedly from the Australian one containing mainly quercetin, isorhamnetin, chrysin and luteolin. The method was proposed for the authenticity test of honey floral origin [162],... 

Fig. 2.67. A typical chromatogram of flavonols in tea leaves. The chromatographic conditions are described in the text. 1 = myricetin 2 = quercetin 3 = kaempferol. Reprinted with permission from. H. Wang et al. [182],...

Fig. 2.71. HPLC chromatogram of the neutral (a) and acidic fractions (b) and the acid-catalysed hydrolysed product of freshly squeezed cranberry juice (c) at 280 nnm. Peaks in a 1 = ( + )-cate-chin 2 = myicetin 3 = quercetin (added as internal standard). Peaks in b 1 = anthocyanin derivative I 2 = benzoic acid 3 = p-anisic acid 4 = quercetin (added as internal standard). Peaks in c 1 = ( + )-catechin 2 = anthocyanin derivative I 3 = anthocyanin derivative II 4 = benzoic acid 5 = anthocyanin derivative III 6 = p-anisic acid 7 = myricetin 8 = quercetin. Reprinted with permission from H. Chen et al. [188].

Fig. 2.79. Chromatograms of a white (I) and red wine sample (II). (LC-DAD signals at three different wavelenghts 256, 324, 365 nm). Peak identification 1 = gallic acid 2 = protocatechuic acid 3 = p-hydroxybenzoic acid 4 = vanillic acid 5 = caffeic acid 6 = (+)-catechin 7 = syringic acid 8 = p-coumaric acid 9 = ( — )-epicatechin 10 = ferulic acid 11 = fraras-resveratrol 12 = rutin 13 = myricetin 14 = cw-resveratrol 15 = quercetin A = caftaric acid B = coutaric acid. Reprinted with permission from M. Castellari et al. [196],...

Fig. 2.88. Chromatograms obtained from standard, onion, wine and plasma samples, (a) standard polyhydro xyflavones (5.00/ig/ml of each), (b) onion skin etract, (c) wine, and (d) plasma spiked with quercetin (5.00/ig/ml). Detection at 370 nm. Peaks 1 = rutin 2 = myricetin 3 = fisetin (internal standard) 4 = morin 5 = quercetin 6 = kaempferol. Reprinted with permission from H. Tsuchiya [210].

Liu IM, Tzeng TF, Liou SS, Lan TW. (2007) Improvement of insulin sensitivity in obese Zucker rats by myricetin extracted from Abelmoschus moschatus. Planta Med 73 1054-1060. 

---