Molecular structure of the flavone backbone (2-phenyl-1,4-benzopyrone)

Isoflavan structure

Neoflavonoids structure

Flavonoids (or bioflavonoids) (from the Latin word flavus meaning yellow, their colour in nature), are a class of plant secondary metabolites.

Flavonoids were referred to as Vitamin P (probably due to the effect they had on the permeability of vascular capillaries) from the mid-1930s to early 50s, but the term has since fallen out of use.^[1]

According to the IUPAC nomenclature,^[2] they can be classified into:

• flavonoids, derived from 2-phenylchromen-4-one (2-phenyl-1,4-benzopyrone) structure (examples: quercetin, rutin).
• isoflavonoids, derived from 3-phenylchromen-4-one (3-phenyl-1,4-benzopyrone) structure
• neoflavonoids, derived from 4-phenylcoumarine (4-phenyl-1,2-benzopyrone) structure.

Classification

The three flavonoid classes above are all ketone-containing compounds, and as such, are flavonoids and flavonols. This class was the first to be termed "bioflavonoids." The terms flavonoid and bioflavonoid have also been more loosely used to describe non-ketone polyhydroxy polyphenol compounds which are more specifically termed flavanoids, flavan-3-ols (or catechins).

Biosynthesis[link]

Functions of flavonoids in plants[link]

Flavonoids are widely distributed in plants fulfilling many functions.

Flavonoids are the most important plant pigments for flower coloration producing yellow or red/blue pigmentation in petals designed to attract pollinator animals.

In higher plants, Flavonoids are involved in UV flitration, symbiotic nitrogen fixation and floral pigmentation.

They may act as a chemical messenger or physiological regulator, they can also act as cell cycle inhibitors.

Flavonoids secreted by the root of their host plant help Rhizobia in the infection stage of their symbiotic relationship with legumes like peas, beans, clover, and soy. Rhizobia living in soil are able to sense the flavonoids and this triggers the secretion of Nod factors, which in turn are recognized by the host plant and can lead to root hair deformation and several cellular responses such as ion fluxes and the formation of a root nodule.

In addition, some flavonoids have inhibitory activity against organisms that cause plant disease e.g. Fusarium oxysporum.^[3]

Potential salutary effects on human health[link]

Flavonoids (specifically flavanoids such as the catechins) are "the most common group of polyphenolic compounds in the human diet and are found ubiquitously in plants".^[4] Flavonols, the original bioflavonoids such as quercetin, are also found ubiquitously, but in lesser quantities.

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. Preliminary research indicates that flavonoids may modify allergens, viruses, and carcinogens, and so may be biological "response modifiers". In vitro studies show that flavonoids also have anti-allergic, anti-inflammatory,^[5] anti-microbial,^[6][7] anti-cancer,^[8] and anti-diarrheal activities.^[9]

Antioxidant activity in vitro[link]

Flavonoids (both flavonols and flavanols) are most commonly known for their antioxidant activity in vitro. At high experimental concentrations that would not exist in vivo, the antioxidant abilities of flavonoids in vitro may be stronger than those of vitamin C and E, depending on concentrations tested.^[10]

Consumers and food manufacturers have become interested in flavonoids for their possible medicinal properties, especially their putative role in inhibiting cancer or cardiovascular disease. Although physiological evidence is not yet established, the beneficial effects of fruits, vegetables, tea, and red wine have sometimes been attributed to flavonoid compounds.

Negligible antioxidant properties of flavonoids in vivo[link]

A research team at the Linus Pauling Institute and the European Food Safety Authority state that flavonoids, inside the human body, are of little or no direct antioxidant value.^[11][12][13] Body conditions are unlike controlled test tube conditions, and the flavonoids are poorly absorbed (less than 5%), with most of what is absorbed being quickly metabolized and excreted.

The increase in antioxidant capacity of blood seen after the consumption of flavonoid-rich foods may not be caused directly by the flavonoids themselves, but is probably due to increased production of uric acid resulting from excretion of flavonoids from the body.^[14] 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."

Potential anti-cancer activity[link]

Flavonoids might induce mechanisms that affect cancer cells and inhibit tumor invasion.^[14] In preliminary studies, UCLA cancer researchers proposed that smokers who ate foods containing certain flavonoids, such as the flavan-3-ols (catechins) found in strawberries and green and black teas, kaempferol from brussel sprouts and apples, and quercetin from beans, onions and apples, may have reduced risk of developing lung cancer.^[15]

Potential deleterious effects on human health[link]

Carcinogenic potential[link]

Flavonoids were found to be strong topoisomerase inhibitors and induce DNA mutations in the MLL gene, which are common findings in neonatal acute leukemia.^[16][17] The DNA changes were increased by treatment with flavonoids in cultured blood stem cells.^[18] In one study, a high flavonoid-content diet in mothers seemed to increase risk of MLL+ acute myeloid leukemia in neonates. This result was not statistically significant though, and when the data on all types of leukiama in the study were taken together, a beneficial effect of the high-flavonoid diet was seen.^[19][20][21]

Natural phenols (flavonoids in one set of experiments and delphinidin in another^[22]) were found to be strong topoisomerase inhibitors, similar to some chemotherapeutic anticancer drugs including etoposide and doxorubicin.^[23] This property may be responsible for both an anticarcinogenic-proapoptotic effect and a carcinogenic, DNA damaging potential of the substances.

Example flavonoids[link]

This article is outdated. Please update this article to reflect recent events or newly available information. Please see the talk page for more information. (December 2010)

Quercetin[link]

Quercetin

Quercetin, a flavonoid and more specifically a flavonol, is the aglycone form of other flavonoid glycosides, such as rutin and quercitrin, found in citrus fruit, buckwheat and onions. Quercetin forms the glycosides, quercitrin and rutin, together with rhamnose and rutinose, respectively.

Although there is preliminary evidence that asthma, lung cancer and breast cancer are lower among people consuming higher dietary levels of quercetin,^[24] the U.S. Food and Drug Administration (FDA), EFSA and the American Cancer Society have concluded that no physiological role exists. The American Cancer Society states that dietary quercetin "is unlikely to cause any major problems or benefits."^[25]

Epicatechin[link]

Epicatechin (EC)

Epicatechin may improve blood flow and has potential 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 vitro.^[26][27] In the test outlined above, it appears the potential antioxidant effects in vivo are minimal as the antioxidants are rapidly excreted from the body.

Dietary sources[link]

This article is outdated. Please update this article to reflect recent events or newly available information. Please see the talk page for more information. (December 2010)

Good sources of flavonoids include all citrus fruits, berries, ginkgo biloba, onions^[28][29] (particularly red onion^[30]), parsley,^[31] pulses,^[32] tea (especially white and green tea), red wine, seabuckthorn, and dark chocolate (with a cocoa content of seventy percent or greater).

Citrus[link]

A variety of flavonoids are found in citrus fruits, including grapefruit.

The citrus bioflavonoids include hesperidin (a glycoside of the flavanone hesperetin), quercitrin, rutin (two glycosides of the flavonol quercetin), and the flavone tangeritin. In addition to possessing in vitro antioxidant activity and an ability to increase intracellular levels of vitamin C, rutin and hesperidin may have beneficial effects on capillary permeability and blood flow. They also exhibit anti-allergy and anti-inflammatory benefits of quercetin from in vitro studies. Quercetin can also inhibit reverse transcriptase, part of the replication process of retroviruses.^[33] The therapeutic relevance of this inhibition has not been established. Hydroxyethylrutosides (HER) have potential for use in the treatment of abnormal capillary permeability, bruising, hemorrhoids, and varicose veins.

Tea[link]

Wine[link]

Dark chocolate[link]

Flavonoids exist naturally in cacao, but because they can be bitter, they are often removed from chocolate, even dark chocolate.^[34] Although flavonoids are present in milk chocolate, milk may interfere with their absorption.^[35][36]

Subgroups[link]

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 (for further reading see ^[37]):

Flavones[link]

Flavones are divided into four groups:^[38]

Group	Skeleton				Examples
	Description	Functional groups		Structural formula
		3-hydroxyl	2,3-dihydro
Flavone	2-phenylchromen-4-one	✗	✗		Luteolin, Apigenin, Tangeritin
Flavonol or 3-hydroxyflavone	3-hydroxy-2-phenylchromen-4-one	✓	✗		Quercetin, Kaempferol, Myricetin, Fisetin, Isorhamnetin, Pachypodol, Rhamnazin
Flavanone	2,3-dihydro-2-phenylchromen-4-one	✗	✓		Hesperetin, Naringenin, Eriodictyol, Homoeriodictyol
Flavanonol or 3-Hydroxyflavanone or 2,3-dihydroflavonol	3-hydroxy-2,3-dihydro-2-phenylchromen-4-one	✓	✓		Taxifolin (or Dihydroquercetin), Dihydrokaempferol

Isoflavones[link]

• Isoflavones

  Isoflavones use the 3-phenylchromen-4-one skeleton (with no hydroxyl group substitution on carbon at position 2).

  Examples: Genistein, Daidzein, Glycitein

Flavan-3-ols, Flavan-4-ols, Flavan-3,4-diols, and proanthocyanidins[link]

Flavan structure

Derivatives of flavan.

Skeleton	Name
	Flavan-3-ol
	Flavan-4-ol
	Flavan-3,4-diol (leucoanthocyanidin)

• Flavan-3-ols (also known as flavanols) and Proanthocyanidins

  Flavan-3-ols use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton.

  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)

  Proanthocyanidins are dimers, trimers, oligomers, or polymers of the flavanols.

Anthocyanidins[link]

Flavylium skeleton of anthocyanidins

• 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[link]

Several recent research articles have demonstrated the efficient production of flavonoid molecules from genetically-engineered microorganisms.^[39][40][41]

Scientists who worked on flavonoids[link]

Jeffrey Harborne investigated the role of flavonoids in interactions between plants and insects. He also investigated the relationship between anthocyanins and the ecology of pollination. He has published on chemotaxonomy as in his research articles on the prevention of anthocyanins, flavones and auron in the primrose family (Primulaceae), in snapdragons (Antirrhinum) and a number of other plants. He also published on isoflavones and chemical ecology.

See also[link]

References[link]

Further reading[link]

• Andersen, Ø.M. / Markham, K.R. (2006). Flavonoids: Chemistry, Biochemistry and Applications. CRC Press. ISBN 978-0-8493-2021-7
• Grotewold, Erich (2007). The Science of Flavonoids. Springer. ISBN 978-0-387-74550-3
• Comparative Biochemistry of the Flavonoids, by J.B. Harborne, 1967 (Google Books)

External links[link]

• Flavonoids (chemistry)
• Micronutrient Information Center - Flavonoids
• Flavonoid Composition of Fruit Tissues of Citrus Species

Databases[link]

• FlavonoidViewer.jp (Japanese, English), a database on flavonoids by Arita Group (Univ of Tokyo, RIKEN Plant Science Center, and Keio Univ), Nishioka Group (Kyoto and Keio Univ) and Kanaya Group (NAIST)
• USDA Database of Flavonoid content of food (pdf)

This article may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (April 2008)

Paul Beatty (born 1962 in Los Angeles) is a contemporary African-American author. Beatty received an MFA in creative writing from Brooklyn College and an MA in psychology from Boston University. A 1980 graduate of El Camino Real High School in Woodland Hills, California.

In 1990, Paul Beatty was crowned the first ever Grand Poetry Slam Champion of the Nuyorican Poets Cafe.^[1] One of the prizes for winning that championship title was the book deal which resulted in his first volume of poetry, Big Bank Takes Little Bank.^[2] This would be followed by another book of poetry Joker, Joker, Deuce as well as appearances performing his poetry on MTV and PBS (in the series The United States of Poetry).^[3] In 1993, he was awarded a grant from the Foundation for Contemporary Arts Grants to Artists Award.

His first novel, The White Boy Shuffle received a positive review in the New York Times. The reviewer, Richard Bernstein, called the book "a blast of satirical heat from the talented heart of black American life."^[4] His second book, Tuff received a positive notice in Time Magazine.^[5] Most recently, Beatty edited an anthology of African-American humor called Hokum and wrote an article in the New York Times on the same subject.^[6]

Novels[link]

• The White Boy Shuffle (1996) ISBN 0-312-28019-X
• Tuff (2000) Alfred A. Knopf, ISBN 0-375-40122-9
• Slumberland (2008)

Edited volume[link]

• Hokum: An Anthology of African-American Humor (2006)

Poetry[link]

• Big Bank Take Little Bank (1991) ISBN 0-9627842-7-3
• Joker, Joker, Deuce (1994) ISBN 0-14-058723-3

Notes[link]

1. ^ Aptowicz, Cristin O'Keefe. (2008) Words in Your Face: A Guided Tour Through Twenty Years of the New York City Poetry Slam. Soft Skull Press. Page 45. ISBN 1-933368-82-9.
2. ^ Aptowicz, Page 46.
3. ^ Aptowicz, Page 80.
4. ^ "Black Poet's First Novel Aims the Jokes Both Ways", New York Times 31 May 1996.
5. ^ "Tuff", Time Magazine 1 May 2000.
6. ^ "Black Humor", New York Times 22 January 2006.

External links[link]

• Article in NY Times by Paul Beatty
• NY TImes review of Paul Beatty's first novel, The White Boy Shuffle
• African American Literature Book Club for Paul Beatty
• Excerpt from Slumberland at BookBrowse

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