Flavonoid characteristics

Clark-Lewis J W, Dainis I 1967 Flavan derivatives. XIX. Teracacidin and isoteracacidin from ca-cia obtusifolia and Acacia maidenii heartwoods Phenolic hydroxylation patterns of heartwood flavonoids characteristic of sections and subsections of the genus Acacia. Aust J Chem 20 2191-2198... 

Ogawa, K., Kawasaki, A., Omnra, M., Yoshida, T., Ikoma, Y. and Yano, M., 2001. 3, 5 -Di-C-beta-glucopyranosylphloretin, a flavonoid characteristic of the genns Fortunella. Phytochemistry Phytochemistry 57(5), 737-742. 

Fig. 3. The regular structure of a procyanidin-type condensed tannin showing characteristic 4,8 interflavonoid bonds linking the flavonoid units.

Some phenolic acids such as ellagic acid can be used as floral markers of heather honey (Cherchi et al., 1994 Ferreres et al., 1996a,b), and the hydroxyciimamates (caffeic, p-coumaric, and ferulic acids) as floral markers of chestnut honey (Cherchi et al., 1994). Pinocembrin, pinobanksin, and chrysin are the characteristic flavonoids of propolis, and these flavo-noid compounds have been found in most European honey samples (Tomas-Barberan et al., 2001). However, for lavender and acacia honeys, no specific phenolic compoimds could be used as suitable floral markers (Tomas-Barberan et al., 2001). Other potential phytochemical markers like abscisic acid may become floral markers in heather honey (Cherchi et al., 1994). Abscisic acid was also detected in rapeseed, lime, and acacia honey samples (Tomas-Barberan et al., 2001). Snow and Manley-Harris (2004) studied antimicrobial activity of phenolics. 

The classic seed burial studies of W. J. Beal and his successors have shown seeds of at least one weed species, Moth Mullein (Verbascum blattaria L.) can remain viable in soil for a peiod of 100 years, whereas three species continued to germinate after 80 years of burial (30). Weed seeds not only resist decay by soil microbes, but they vary in dormancy characteristics. There is considerable evidence that chemical inhibitors are responsible for both phenomena. Unsaturated lactones and phenolic compounds in particular, are potent antimicrobial compounds present in many seeds (4J. Fruits and seeds are also known to contain diverse germination inhibitors including phenolic compounds, flavonoids and/or their glycosides and tannins. Unique methods to destroy inhibitors could provide an excellent weed management strategy. 

Several general characteristics of the results compiled in Table I are worthy of mention. Compared to the variety of chemicals postulated to be involved in allelopathy (1), few specific compounds have been tested for inhibition of mineral absorption. The most extensively studied compounds are the phenolic acids, probably because of their being ubiquitously found in nature (1). Also, several flavonoids are inhibitory to mineral absorption (Table I). Both of these groups of compounds are often cited as being responsible for allelopathic interactions between plants. 

Phytochemicals or phytonutrients are bioactive substances that can be found in foods derived from plants and are not essential for life the human body is not able to produce them. Recently, some of their characteristics, mainly their antioxidant capacity, have given rise to research related to their protective properties on health and the mechanisms of action involved. Flavonoids are a diverse group of phenolic phytochemicals (Fig. 6.1) that are natural pigments. One function of flavonoids is to protect plants from oxidative stress, such as ultraviolet rays, environmental pollution, and chemical substances. Other relevant biological roles of these pigments are discussed in other chapters of this book. 

These structurally diverse compounds exhibit a range of biological activities in vitro that may explain their potential health-promoting properties, including antioxidant and anti-inflammatory effects and the induction of apoptosis (Hooper and others 2008). Most of the recent interest in flavonoids as health-promoting compounds is related to their powerful antioxidant properties. The criteria to establish the antioxidant capacity of these compounds is based on several structural characteristics that include (a) the presence of o-dihydroxyl substituents in the B-ring (b) a double bond between positions 2 and 3 and (c) hydroxyl groups in positions 3 and 5. 

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). 

All four bases consist of two units a pyrrolidine and a flavonoid (or flavan), and their spectra present characteristics of both parts. Thus the UV and IR spectra resemble the spectra of the parent flavonoid (chrysine for 61 and 62, hispidulin for 64, and 4, 5-dihydroxy-7-methoxyflavan for 63). The mass spectra of 61, 62, and 63 do not easily give a molecular ion but rather show fragments pertaining to the flavonoid and to the pyrrolidine parts [m/e 84 and 83 (61 and... 

It was stated that the chromatographic analysis of the flavonoid profde may help the determination of taxonomic relationships between these species [125], The optimization of the separation of flavonoid glycosides of Mentha piperita (Laminaceae) was carried out on silica, amino, cyano and C18 HPTLC statinoary phases. The investigation was motivated by the spasmolytic, carminative and cholagogue characteristics of the plant. Air-dried and powdered leaves of peppermint (300 g) were extracted with methanol-water 1 1 v/v at ambient temperature. The suspension was filtered, concentrated to 200 ml acidified to pH 3 with formic acid and separated in an ODS column (400 X 40 mm i.d. particle size 40 pm). 

The separation characteristics of unmodified silica, diol, cyano, cellulose and RP-18 stationary phases were compared for the analysis of ellagitannins, gallotannins and flavonoid glycosides in the aerial parts of Erodium cicutarum (Geraniaceae) (stork s bill). Its decoction has been used in cases of dysentery, fever, wounds and worm infections. The air-dried and powdered plant material (300 g) was extracted three times with water-acetone (1 1, v/v) at ambient temperature. The collected extract was filtered and concentrated. The aqueous phase was acidified to pH 3 with formic acid and separated in an ODS column. Polphenols... 

It was established that the selectivity of the alumina layer is higher than that of polyamide, therefore, its application for the separation of coumarins and flavonoids was proposed [131], The adsorption characteristics of Florisil and silica were studied using a similar set of coumarins and flavonoids as in references [130] and [131], The parameters of the equation describing the dependence of the RM value on the concentration of the stronger component in the binary mobile phase are listed in Table 2.43. 

As the separation characteristics of liquid chromatographic and electrophoretic techniques markedly differ from each other, combined methods using the advantages of both procedures have been successfully used for the analysis of flavonoids. Thus, the use of CZE-UV, HPTLC-UV and GC-MS for the measurement of flavonoids in seeds and root exudates of Lotus pedunculatus has been reported. The rooting solution and seed exudate were passed through cellulose acetate filters to bind the flavonoids. After extraction,... 

In an attempt to influence flavor characteristics, CHS antisense and overexpression constructs were introduced into grapefruit by Agrobacterium tumefaciens [16, 59]. CHS overexpression constructs were shown to lead to morphological abnormalities and frequently to death, while a number of CHS antisense constructs resulted in a statistically significant reduction in flavonoid content in the transgenic plants even though there was a large variation in the flavonoid concentration [16]. 

Regulation of Flavonoid Synthesis in C. americanum. Biosynthesis of methylated flavonol glucosides seems to be under tight regulation, not only by the substrate specificity of the enzymes involved, but also by other factors, among which are (a) the strict position specificity of these enzymes towards their hydroxylated or partially methylated substrates (b) the apparent difference in microenvironment of the different methyl-transferases, whereby those earlier in the pathway utilized aglycones whereas later enzymes accepted only glucosides as substrates (c) the subtle characteristic differences in methyl-transferases with respect to their pH optima, pi values and requirement for Mg ions, despite their similar molecular size ... 

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