Plant flavonols

STs are simple phenols such as 4-nitrophenol, phenolic catecholamine neurotransmitters such as dopamine, phenolic steroids such as the estrogens, non-phenolic hydroxy-steroids such as dehydroepiandrosterone (DHEA) and in plants, flavonols such as quercetin. Cytosolic STs are also actively involved in the Al-sulfation of alkyl- and aryl-amines, as well as alkyl- and arylamides leading in some cases to the formation of unstable metabolites. 

Hardigree, A.A. and Epier, J.L. (1977). Mutagenicity of plant flavonols In microbial systems. Abstr. 8th Ann. Mto. Environmental Mutaoen Society. Colorado Springs, Colorado, p. 48. 

Meltz, M.L. and MacGregor, J.T. (1981). Activity of the plant flavonol quercetin in the mouse lymphoma L5178Y TK " mutation, DNA single-strand break and BALB/c 3T3 chemical transformation assays. Mutat. Res. 88, 317-324. 

Varin L, DeLuca V, Ibrahim RK et al (1992) Molecular characterization of two plant flavonol sulfotransferases. Proc Natl Acad Sci USA 89 1286-1290... 

Brown J P, Dietrich P S 1979 Mutagenicity of plant flavonols in the salmonella mammalian microsome test. Activation of flavonol glycoside by mixed glycosidases from rat fecal bacteria and other sources. Mutat Res 66 223-240... 

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. 

Phlomis consists of about 100 species, a dozen of which occur in Mediterranean Europe (Mabberley, 1997, p. 549). The study of interest here involves a study of the flavonoids of R lychnitys L., a small plant native to Mediterranean Spain (Tomas et ah, 1986). Those workers identified the common flavones apigenin, luteolin, and luteolin 3 -methyl ether (chrysoeriol) 7-0-glucosides and their respective /7-coumaroyl derivatives. A brief review of the literature revealed that Mediterranean species of Phlomis are characterized by the presence of the flavone methyl ether, whereas continental species appear to lack 0-methylated flavones. Species from India have been reported to lack flavones but accumulate flavonols. The suggestion was made that accumulation of flavonols represents an ancestral feature of the genus. 

The chemical formulae for a variety of plant phenols are given in Fig. 16.2, including examples of simpler phenols, such as cinnamic acid derivative, and of tocopherols, flavonoids, flavonoid glycosides and anthocyanidins. The flavonoids include the following subclasses flavanones (taxifolin), flavones (luteolin), flavonols (quercetin) and flavanols (catechin/epicatechin). The... 

Asen, S., Eactors affecting formation of anthocyanin-flavonol co-pigment complexes and their importance on flower color. Plant Physiol, 47, 20, 1971. 

Ibdah, M. et al.. Spectral dependence of flavonol and betacyanin accnmnlation in Mesembryanthemum crystallinum nnder enhanced nltraviolet radiation. Plant Cell Environ., 25, 1145, 2002. 

Many recent stndies of NMR spectroscopy have been reported for structure elucidation of anthocyanins from many plant materials such as carrot, tart berries, boysenberries, " flowers, black soybeans, and anthocyanin and flavonol derivatives in red wine. Ginsti et al. (1998) structurally elucidated two novel diacylated anthocyanins and two monoacylated anthocyanins from radish Raphanus sativus) by one- and two-dimensional NMR. Anderson et al. (2006) applied two-dimensional NMR to characterize carboxypyranoanthocyanins. Two 3-deoxyantho-cyanins, lnteolinidin-5-glncoside, and apigeninidin-5-glucoside were identified by Swinny et al. nsing H and C NMR. 

Bovy A, de Vos R, Kemper M, Schijlen E, Almenar PM, Muir S, Collins G, Robinson S, Verhoeyen M, Hughes S, Santos-Buelga C and van Tunen A. 2002. High-flavonol tomatoes resulting from the heterologous expression of the maize transcription factor genes LC and Cl. Plant Cell 14 2509-2526. 

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

---