Secondary metabolisms flavonoids

Seigler D. (1998) Flavonoids. Plant Secondary Metabolism. Norwell Kluwer Academic Publishers, pp. 151-192. 

DONG, X., BRAUN, E.L., GROTEWOLD, E., Functional conservation of plant secondary metabolic enzymes revealed by complementation of Arabidopsis flavonoid mutants with maize genes, Plant Physiol., 2001,127,46-57. 

Methylation is one of the most common enzymatic modifications in plant specialized (secondary) metabolism. Almost all classes of plant specialized metabolites are known to be methylated, including amino acids, alkaloids, phenylpropanoids, sugars, purines, sterols, thiols, and flavonoids. The methyl transfer most commonly occurs on C, N, S, or O atoms. 

Widyarini S, Spinks N, Husband AJ, Reeve VE (2001) Isoflavonoid compounds from red clover Trifolium pratense) protect from inflammation and immune suppression induced by UV radiation. Photochem Photobiol 74(3) 465 70 Williams CA, Goldstone F, Greenham J (1996) Flavonoids, cinnamic acids and coumarins from the different tissues and medicinal preparations of Taraxacum officinale. Phytochemistry 42(1) 121-127 Williams CA, Harborne JB, Geiger H, Hoult JR (1999) The flavonoids of Tanacetum parthenium and T. vulgare and their anti-inflammatory properties. Phytochemistry 51(3) 417 23 Wink M (1999) Introduction biochemistry, role and biotechnology of secondary metabolites. In Wink M (ed) Biochemistry of plant secondary metabolism, vol 2, Annual plant reviews. CRC Press, Boca Raton, pp 1-16... 

Coordinated regulation of the activity of enzymes of one biosynthetic pathway seems to occur frequently in secondary metabolism (see, e.g.. Figs. 7 and 8). It has been examined in detail in the flavonoid metabolism of higher plants. 

Higher plants produce diverse chemicals such as alkaloids, terpenoids, and phenolic compounds (phenylpropanoids and flavonoids) in secondary metabolism. Among these chemicals, benzylisoquinoline alkaloids (BIAs) are very important in medicine due to their high biological activities. However, extraction yields from plants are low because most of these metabolites accumulate at low levels in plant cells. There has been increasing interest in the microbial... 

Havanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthocyanidins), flavan-4-ols, and flavan-3,4-diols. They arise from plant secondary metabolism through condensation of phenylalanine derived from the shikimate pathway with malonyl-CoA obtained from citrate that is produced by the tricarboxylic acid cycle, leading to the formation of the key precursor in the flavonoids biosynthesis the naringenin chalcone. The exact nature of the molecular species that undergo polymerization and the mechanism of assembly in proanthocyanidins are still unknown. From a structural point of view, flavanols... 

One of the main reasons for this lack of concretion is the complexity of plant matrices, whose diversified secondary metabolism includes a vast number of different compounds with close structures that can be hard to identify. Some of these families with a well-documented bibliography related to health effects comprise alkaloids, phenolic compounds (including phenolic acids, stilbenes like resveratrol, or flavonoids such as anthocyanins, procyanidins, or isoflavones), terpenoids, carotenoids, sulfur compounds (such as glucosinolates and isothiocyanates), etc. Their presence and amount in the plant source depend on multiple factors including variety, organ of the plant, soil, sun exposure, climate, or even ways of cultivation. 

Secondary metabolism, and in particular phenolic metabolism, largely depends on external factors such as light, temperature, and various stresses [64], Although this has been mainly studied in relation to flavonoid production, we report here only information related to phenolic acids. 

Phenolic compounds are widespread products of secondary metabolism of lichen, and antioxidant activity is most frequently associated with their presence. Lichen phenolics are mainly depsides, depsidones and dibenzofurans, whereas vascular plant phenolics include tannins, lignins and flavonoids. Orsellinic acid is the basic unit in the biosynthesis of hchen phenolics. Lichen phenols are generally secreted by the fungal partner and deposited as crystals on the surface of the ceU wall of the fungal hyphae. Lichen phenols are primarily acetate-polymalonate derived with the exception of pulvinic acid derivates which are synthesised via... 

Such complexes include fatty acid synthases (FASes), elongases (ELSes) and polyketide synthases (PKSes) which can fimction individually or in concert. FAS synthesizes the 16 and 18 carbon acyl chains of membrane lipids as well as those of the plant cutin and suberin monomers. ELSes use these acyl chains as primers to synthesize longer ones for storage lipids in some seeds and for cuticular and epicuticular waxes. PKSes participate in a wide range of secondary metabolic pathways. In plants chalcone synthase contributes to the carbon skeleton of the flavonoids, in fungi and bacteria, especially... 

Fig. 6.1. Some relationships between primary and secondary metabolism. The probable origins are shown of the flavonoid, phenylpropanoid and isoprenoid group of compounds. The other groups discussed in the text, the non-protein amino acids and alkaloids, arise from a number of points in primary metabolism and only the origins of the tropane and pyrrolidine alkaloids from ornithine and proline and the indole alkaloids from tryptophan are shown.

E) coumarins, (F) quinones, (G) flavonoids, (H) tannins, (I) alkaloids, (J) terpenoids and steroids and (K) miscellaneous and unknowns. Although many of these compounds are secondary products of plant metabolism, several are also degradation products which occur in the presence of microbial enzymes. 

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