1. • Flavonoid
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• Molecular structure of the flavone backbone (2-phenyl-1,4-benzopyrone)
• The term flavonoid refers to a class of plant secondary metabolites.
According to the IUPAC nomenclature,[1] they can be classified into:
• flavonoids, derived from 2-phenylchromen-4-one (2-phenyl-1,4-
benzopyrone) structure
• isoflavonoids, derived from 3-phenylchromen-4-one (3-phenyl-1,4-
benzopyrone) structure
• neoflavonoids, derived from 4-phenylcoumarine (4-phenyl-1,2-
benzopyrone) structure.
• Flavonoids are most commonly known for their antioxidant activity.
However, it is now known that the health benefits they provide against
cancer and heart disease are the result of other mechanisms.[2] Flavonoids are
also commonly referred to as bioflavonoids in the media – the terms are
equivalent and interchangeable, for flavonoids are biological in origin.
• Biosynthesis
• Flavonoids are synthesized by the phenylpropanoid metabolic pathway in
which the amino acid phenylalanine is used to produce 4-coumaroyl-CoA.
This can be combined with malonyl-CoA to yield the true backbone of
flavonoids, a group of compounds called chalcones which contain two
phenyl rings (see polyphenols). Conjugate ring-closure of chalcones results
in the familiar form of flavonoids, the three-ringed structure of a flavone.
The metabolic pathway continues through a series of enzymatic
modifications to yield flavanones → dihydroflavonols → anthocyanins.
Along this pathway many products can be formed, including the flavonols,
flavan-3-ols, proanthocyanidins (tannins) and a host of other polyphenolics.
• Biological effects
• Flavonoids are widely distributed in plants fulfilling many functions
including producing yellow or red/blue pigmentation in flowers and
protection from attack by microbes and insects. The widespread distribution
of flavonoids, their variety and their relatively low toxicity compared to
other active plant compounds (for instance alkaloids) mean that many
animals, including humans, ingest significant quantities in their diet.
Flavonoids have been referred to as "nature's biological response modifiers"
because of strong experimental evidence of their inherent ability to modify
the body's reaction to allergens, viruses, and carcinogens. They show anti-
allergic, anti-inflammatory[3] , anti-microbial and anti-cancer activity.
• Consumers and food manufacturers have become interested in flavonoids for
their medicinal properties, especially their potential role in the prevention of
cancers and cardiovascular disease. The beneficial effects of fruit,
vegetables, and tea or even red wine have been attributed to flavonoid
compounds rather than to known nutrients and vitamins.
• Health benefit not due to direct antioxidant value
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2. • In 2007, research conducted at the Linus Pauling Institute and published in
Free Radical Biology and Medicine indicates that inside the human body,
flavonoids themselves are of little or no direct antioxidant value. Unlike in
the controlled conditions of a test tube, flavonoids are poorly absorbed by
the human body (less than 5%), and most of what is absorbed is quickly
metabolized and excreted from the body.
• The huge increase in antioxidant capacity of blood seen after the
consumption of flavonoid-rich foods is not caused directly by the flavonoids
themselves, but most likely is due to increased uric acid levels that result
from expelling flavonoids from the body.[2] According to Frei, "we can now
follow the activity of flavonoids in the body, and one thing that is clear is
that the body sees them as foreign compounds and is trying to get rid of
them. But this process of gearing up to get rid of unwanted compounds is
inducing so-called Phase II enzymes that also help eliminate mutagens and
carcinogens, and therefore may be of value in cancer prevention...
Flavonoids could also induce mechanisms that help kill cancer cells and
inhibit tumor invasion."[2]
• Their research also indicated that only small amounts of flavonoids are
necessary to see these medical benefits. Taking large dietary supplements
provides no extra benefit and may pose some risks.[2]
• Diarrhea
• A study done at Children's Hospital & Research Center Oakland, in
collaboration with scientists at Heinrich Heine University in Germany, has
shown that epicatechin, quercetin and luteolin can inhibit the development of
fluids that result in diarrhea by targeting the intestinal cystic fibrosis
transmembrane conductance regulator Cl– transport inhibiting cAMP-
stimulated Cl– secretion in the intestine.[4]
• Important flavonoids
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• Quercetin
• Quercetin is a flavonoid and more specifically a flavonol (see below), that
constitutes the aglycone of the glycoside rutin. In studies, quercetin is found
to be the most active of the flavonoids, and many medicinal plants owe
much of their activity to their high quercetin content. Quercetin has
demonstrated significant anti-inflammatory activity because of direct
inhibition of several initial processes of inflammation. For example, it
inhibits both the production and release of histamine and other
allergic/inflammatory mediators. In addition, it exerts potent antioxidant
activity and vitamin C-sparing action. It has been found to be anti-cancer.
Quercetin can be found in the herbal products based on Hawthorn which are
used for acute symptoms of Congestive Heart Failure.
• Epicatechin
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3. • Epicatechin improves blood flow and thus seems good for cardiac health.
Cocoa, the major ingredient of dark chocolate, contains relatively high
amounts of epicatechin and has been found to have nearly twice the
antioxidant content of red wine and up to three times that of green tea in in-
vitro tests.[5] [6] But in the test outlined above it now appears the beneficial
antioxidant effects are minimal as the antioxidants are rapidly excreted from
the body.
• Oligomeric proanthocyanidins
• Proanthocyanidins extracts demonstrate a wide range of pharmacological
activity. Their effects include increasing intracellular vitamin C levels,
decreasing capillary permeability and fragility, scavenging oxidants and free
radicals, and inhibiting destruction of collagen, the most abundant protein in
the body.
• Important dietary sources
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• Good sources of flavonoids include all citrus fruits, berries, onions, parsley,
legumes, green tea, red wine, seabuckthorn, and dark chocolate (that with a
cocoa content of seventy percent or greater).
• Citrus
• The citrus bioflavonoids include hesperidin, quercetin, rutin (a glycoside of
quercetin), and tangeritin. In addition to possessing antioxidant activity and
an ability to increase intracellular levels of vitamin C, rutin and hesperidin
exert beneficial effects on capillary permeability and blood flow. They also
exhibit some of the anti-allergy and anti-inflammatory benefits of quercetin.
Quercetin can also inhibit reverse transcriptase, part of the replication
process of retroviruses.[7] The therapeutical relevance of this inhibition has
not been established. Hydroxyethylrutosides (HER) have been used in the
treatment of capillary permeability, easy bruising, hemorrhoids, and varicose
veins.
• Tea
• Green tea flavonoids are potent antioxidant compounds, thought to reduce
incidence of cancer and heart disease. The major flavonoids in green tea are
the catechins (catechin, epicatechin, epicatechin gallate, and epigallocatechin
gallate (EGCG)).
• In producing teas such as oolong tea and black tea, the leaves are allowed to
oxidize, during which enzymes present in the tea convert some or all of the
catechins to larger molecules. White tea is the least processed of teas and is
shown to present the highest amount of catechins known to occur in camellia
sinensis.However, green tea is produced by steaming the fresh-cut leaf,
which inactivates these enzymes, and oxidation does not significantly occur.
• Wine
• Grape skins contain significant amounts of flavonoids as well as other
polyphenols[8]. Both red and white wine contain flavonoids, however, since
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4. red wine is produced by fermentation in the presence of the grape skins, red
wine has been observed to contain higher levels of flavonoids, and other
polyphenolics such as resveratrol.
• Subgroups
• Over 5000 naturally occurring flavonoids have been characterized from
various plants. They have been classified according to their chemical
structure, and are usually subdivided into the following subgroups:
• Flavones
• Flavones are divided into four groups:[9]
• Flavones
• Flavones use the 2-phenylchromen-4-one skeleton.
• Examples: Luteolin, Apigenin, Tangeritin
• Flavonols
• Flavonols or 3-hydroxyflavones use the 3-hydroxy-2-phenylchromen-4-one
skeleton.
• Examples: Quercetin, Kaempferol, Myricetin, Fisetin, Isorhamnetin,
Pachypodol, Rhamnazin
• Flavanones
• Flavanones use the 2,3-dihydro-2-phenylchromen-4-one skeleton.
• Examples: Hesperetin, Naringenin, Eriodictyol
• 3-Hydroxyflavanones or 2,3-dihydroflavonols
• 3-Hydroxyflavanones use the 3-hydroxy-2,3-dihydro-2-phenylchromen-4-
one skeleton.
• Examples: Dihydroquercetin, Dihydrokaempferol
• Isoflavones
• Isoflavones
• Isoflavones use the 3-phenylchromen-4-one skeleton.
• Examples: Genistein, Daidzein, Glycitein
• Flavan-3-ols and Anthocyanidins
• Flavan-3-ols
• Flavan-3-ols use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton.
• Examples: Catechins (Catechin (C), Gallocatechin (GC), Catechin 3-gallate
(Cg), Gallocatechin 3-gallate (GCg)), Epicatechins (Epicatechin (EC),
Epigallocatechin (EGC), Epicatechin 3-gallate (ECg), Epigallocatechin 3-
gallate (EGCg))
• Anthocyanidins
• Anthocyanidins are the aglycones of anthocyanins. Anthocyanidins use the
flavylium (2-phenylchromenylium) ion skeleton
• Examples: Cyanidin, Delphinidin, Malvidin, Pelargonidin, Peonidin,
Petunidin
• Availability through microorganisms
• A number of recent research articles have demonstrated the efficient
production of flavonoid molecules from genetically-engineered
microorganisms[10].
• References
• ^ Flavonoids (isoflavonoids and neoflavonoids)., IUPAC Compendium of
Chemical Terminology
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5. a b c d
•^ "Studies force new view on biology of flavonoids", by David Stauth,
EurekAlert!. Adapted from a news release issued by Oregon State
University. URL accessed 2007-03-06.
• ^ Therapeutic potential of inhibition of the NF-κB pathway in the treatment
of inflammation and cancer. Yamamoto and Gaynor 107 (2): 135 -- Journal
of Clinical Investigation. Retrieved on 2006-08-30.
• ^ Schuier, Maximilian; Helmut Sies, Beate Illek, and Horst Fischer (October
2005). "Cocoa-Related Flavonoids Inhibit CFTR-Mediated Chloride
Transport across T84 Human Colon Epithelia" (PDF). Journal of Nutrition
135 (10): 2320-2325. Retrieved on 2007-05-02.
• ^ J. Agric.Food Chem. (2003) 51:7292-7295 Lee et al.
• ^ Cocoa nutrient for 'lethal ills'. BBC News. Retrieved on 2007-03-11.
• ^ Spedding, G., Ratty, A., Middleton, E. Jr. (1989) Inhibition of reverse
transcriptases by flavonoids. Antiviral Res 12 (2), 99-110. PMID 2480745
• ^ James A. Kennedy, Mark A. Matthews, and Andrew L. Waterhouse,
Effect of Maturity and Vine Water Status on Grape Skin and Wine
Flavonoids Am. J. Enol. Vitic. 53:4:268-274 (2002) (abstract)
• ^ http://www.ars.usda.gov/is/np/phenolics/illus/phenfig4.htm
• ^ Hwang EI, Kaneko M, Ohnishi Y, Horinouchi S. Production of plant-
specific flavanones by Escherichia coli containing an artificial gene cluster.
Appl Environ Microbiol. 2003 May;69(5):2699-706 PMID 12732539
• Balch, J. F., & Balch, P. A. (2000). Prescription for Nutritional Healing.
New York: Avery, Penguin Putnam Inc.
• Murray, M. T. (1996). Encyclopedia of Nutritional Supplements. Roseville:
Prima Publishing.
• External links
• USDA Database of Flavonoid content of food (pdf)
• Flavonoids (chemistry)
• Flavonoids (chemistry)
• Cornell news on Cocoa
• A Dark Chocolate a Day Keeps the Doctor Away
• Antioxidant in Green Tea may fight Alzheimer's-EGCG
• Therapeutic potential of the NF-kB pathway in the treatment of
inflammatory disorders
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