Flavan-3-ols are a class of flavonoid

Flavonoid

Flavonoids , are a class of plant secondary metabolites....

s that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include the catechins and the catechin gallates.

Flavanols (with an "a") are not to be confused with flavonols (with an "o"), another class of flavonoid

Flavonoid

Flavonoids , are a class of plant secondary metabolites....

s containing a ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

 group.

Flavanols are building blocks for proanthocyanidin

Proanthocyanidin

Proanthocyanidins, also known as OPCs or condensed tannins, are a subgroup of the flavonoid class of polyphenols...

s.

Flavanols possess two chiral carbons meaning there 4 diastereoisomers for each of them.

Catechins are differentiated from the ketone-containing flavonoids such as quercitin and rutin

Rutin

Rutin, also called rutoside, quercetin-3-O-rutinoside and sophorin, is a citrus flavonoid glycoside found in buckwheat, the leaves and petioles of Rheum species, and asparagus...

, which are called flavonols (spelled flavonols with an o). The term bioflavonoid was first used to describe the flavonols, but as an imprecise term has been loosely applied to the larger family of flavonoids, including also the polymeric hydroxyl-only containing flavan-3-ols (catechins).

Sources of catechins

The catechins are abundant in tea

Tea

Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...

s derived from the tea-plant Camellia sinensis

Camellia sinensis

Camellia sinensis is the species of plant whose leaves and leaf buds are used to produce Chinese tea. It is of the genus Camellia , a genus of flowering plants in the family Theaceae. White tea, green tea, oolong, pu-erh tea and black tea are all harvested from this species, but are processed...

as well as in some cocoas

Cocoa solids

Cocoa solids are the low-fat component of chocolate. When sold as an end product, it may also be called cocoa powder, cocoa, and cacao....

 and chocolate

Chocolate

Chocolate is a raw or processed food produced from the seed of the tropical Theobroma cacao tree. Cacao has been cultivated for at least three millennia in Mexico, Central and South America. Its earliest documented use is around 1100 BC...

s (made from the seeds of Theobroma cacao).

Catechins are also present in the human diet in fruits, vegetables and wine and are found in many other plant species.
Flavan-3-ols (sometimes referred to as flavanols) are a class of flavonoid

Flavonoid

Flavonoids , are a class of plant secondary metabolites....

s that use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton. These compounds include the catechins and the catechin gallates.

Flavanols (with an "a") are not to be confused with flavonols (with an "o"), another class of flavonoid

Flavonoid

Flavonoids , are a class of plant secondary metabolites....

s containing a ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

 group.

Flavanols are building blocks for proanthocyanidin

Proanthocyanidin

Proanthocyanidins, also known as OPCs or condensed tannins, are a subgroup of the flavonoid class of polyphenols...

s.

Flavanols possess two chiral carbons meaning there 4 diastereoisomers for each of them.

Catechins are differentiated from the ketone-containing flavonoids such as quercitin and rutin

Rutin

Rutin, also called rutoside, quercetin-3-O-rutinoside and sophorin, is a citrus flavonoid glycoside found in buckwheat, the leaves and petioles of Rheum species, and asparagus...

, which are called flavonols (spelled flavonols with an o). The term bioflavonoid was first used to describe the flavonols, but as an imprecise term has been loosely applied to the larger family of flavonoids, including also the polymeric hydroxyl-only containing flavan-3-ols (catechins).

Catechin and the gallates

Catechin

Catechin

Catechin is a natural phenol antioxidant plant secondary metabolite. The term catechins is also commonly used to refer to the related family of flavonoids and the subgroup flavan-3-ols ....

 and epicatechin are epimer

Epimer

In chemistry, epimers are diastereomers that differ in configuration of only one stereogenic center. Diastereomers are a class of stereoisomers that are non-superposable, non-mirror images of one another....

s, with (-)-epicatechin and (+)-catechin being the most common optical isomer

Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

s found in nature. Catechin was first isolated from the plant extract catechu

Catechu

For the region in India, see Kutch District.Catechu is an extract of any of several species of Acacia—but especially Acacia catechu—produced by boiling the wood in water and evaporating the resulting brew....

, from which it derives its name. Heating catechin past its point of decomposition releases pyrocatechol

Pyrocatechol

Catechol, also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula C6H42. It is the ortho isomer of the three isomeric benzenediols. This colourless compound occurs naturally in trace amounts...

 (also called catechol), which explains the common origin of the names of these compounds.

Epigallocatechin and gallocatechin contain an additional phenolic hydroxyl group when compared to epicatechin and catechin, respectively, similar to the difference in pyrogallol

Pyrogallol

Pyrogallol or benzene-1,2,3-triol is a benzenetriol. It is a white crystalline powder and a powerful reducing agent. It was first prepared by Scheele 1786 by heating gallic acid. An alternate preparation is heating para-chlorophenoldisulphonic acid with potassium hydroxide.When in alkaline...

 compared to pyrocatechol.

Catechin gallates are gallic acid

Gallic acid

Gallic acid is a trihydroxybenzoic acid, a type of phenolic acid, a type of organic acid, also known as 3,4,5-trihydroxybenzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H23COOH. Gallic acid is found both free and as part of...

 ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

s of the catechins; such as epigallocatechin gallate

Epigallocatechin gallate

Epigallocatechin gallate , also known as epigallocatechin 3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin....

 (EGCG), which is commonly the most abundant catechin in tea.

Biosynthesis of (-)-epicatechin

The flavonoids are products from a cinnamoyl-CoA starter unit, with chain extension using three molecules of malonyl-CoA. Reactions are catalyzed by a type III PKS enzyme. These enzyme do not utilize ACPSs, but instead employ coenzyme A esters and have a single active site to perform the necessary series of reactions e.g. chain extension, condensation, cyclization. Chain extension of 4-hydroxycinnamoyl-CoA with three molecules of malonyl-CoA gives initially a polyketide (Figure 1), which can be folded. These allow Claisen-like reactions to occur generating aromatic rings

Figure 1:Schematic overview of the flavan-3-ol (-)-epicatechin biosynthesis in plants. Enzymes are indicated in blue, abbreviated as follows: E1, phenylalanine ammonia lyase (PAL), E2, tyrosine ammonia lyase (TAL), E3, cinnamate 4-hydroxylase, E4, 4-coumaroyl: CoA-ligase, E5, chalcone synthase (naringerin-chalcone synthase), E6, chalcone isomerase, E7, flavonoid 3´-hydroxylase, E8, flavonone 3-hydroxylase, E9, dihydroflavanol 4-reductase, E10, anthocyanidin synthase (leucoanthocyanidin dioxygenase), E11, anthocyanidin reductase. HSCoA, Coenzyme A. L-Tyr, L-Tyrosin, L-Phe, L-Phenylalanine.

Health benefits of catechins

The health benefits of catechins have been studied extensively in humans and in animal models. Reduction in atherosclerotic plaques was seen in animal models. Reduction in carcinogenesis

Carcinogenesis

Carcinogenesis or oncogenesis is literally the creation of cancer. It is a process by which normal cells are transformed into cancer cells...

 was seen in vitro

In vitro

In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

.

Many studies on health benefits

Health benefits of tea

The health effects of tea have been examined ever since the first infusions of Camellia sinensis about 4700 years ago in China. The legendary emperor Shennong claimed in The Divine Farmer's Herb-Root Classic that Camellia sinensis infusions were useful for treating conditions including tumors,...

 have been linked to the catechin content.
According to Norman Hollenberg, professor of medicine at Harvard Medical School

Harvard Medical School

Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....

, epicatechin can reduce the risk of four of the major health problems: stroke, heart failure, cancer and diabetes. He studied the Kuna

Kuna (people)

Kuna or Cuna is the name of an indigenous people of Panama and Colombia. The spelling Kuna is currently preferred. In the Kuna language, the name is Dule or Tule, meaning "people," and the name of the language in Kuna is Dulegaya, meaning "Kuna language" - Location :The Kuna live in three...

 people in Panama

Panama

Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...

, who drink up to 40 cups of cocoa a week, and found that the prevalence of the “big four” is less than 10%. He believes that epicatechin should be considered essential to the diet and thus classed as a vitamin.

According to one researcher epigallocatechin-3-gallate is an antioxidant that helps protect the skin from UV radiation-induced damage

Indirect DNA damage

Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a chromophore that does not have the ability to convert the energy into harmless heat very quickly. Molecules that do not have this ability have a long lived excited state. This long lifetime leads to a high probability...

 and tumor formation.

DNA protection

Catechins, when combined with habitual exercise, have been shown to delay some forms of aging. Mice fed catechins showed decreased levels of aging, lowering of oxidative stress in mitochondria, and an increase in mRNA

Messenger RNA

Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

 transcription of mitochondrial-related proteins.

Possible reduced benefits in treated chocolate

An editorial in The Lancet

The Lancet

The Lancet is a weekly peer-reviewed general medical journal. It is one of the world's best known, oldest, and most respected general medical journals...

medical journal warned against increasing one’s intake of dark chocolate to improve health because the beneficial compounds are sometimes removed due to their bitter taste without an indication on the label. Additionally, such product may be high in lead, and also fat, sugar, and calories, which can increase the risk for heart disease.

Anti-carcinogenic effects

In 2008 UCLA

University of California, Los Angeles

The University of California, Los Angeles is a public research university located in the Westwood neighborhood of Los Angeles, California, USA. It was founded in 1919 as the "Southern Branch" of the University of California and is the second oldest of the ten campuses...

 cancer researchers found that study participants who ate foods containing certain flavonoids seemed to be protected from developing lung cancer

Lung cancer

Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...

. Dr. Zhang, (professor of public health and epidemiology at the UCLA School of Public Health) said the flavonoids that appeared to be the most protective included catechin, found in strawberries and green and black teas; kaempferol

Kaempferol

Kaempferol is a natural flavonol, a type of flavonoid, that has been isolated from tea, broccoli, Delphinium, Witch-hazel, grapefruit,cabbage, kale, beans, endive, leek, tomato, strawberries, grapes, brussels sprouts, apples and other plant sources. Kaempferol is a yellow crystalline solid with a...

, found in Brussels sprouts and apples; and quercetin

Quercetin

Quercetin , a flavonol, is a plant-derived flavonoid found in fruits, vegetables, leaves and grains. It also may be used as an ingredient in supplements, beverages or foods.-Occurrence:...

, found in beans, onions (particularly red) and apples.

Aglycones

Health effects

Flavanols, usually from cocoa beans or tea

Tea

Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...

, are believed to keep arteries flexible, increase small vessel circulation, reduce blood pressure and protect against sunburns

Flavanol-rich chocolate

The Mars Corporation

Mars, Incorporated

Mars, Incorporated is a worldwide manufacturer of confectionery, pet food, and other food products with US$30 billion in annual sales in 2010, and is ranked as the 5th largest privately held company in the United States by Forbes. Headquartered in McLean, unincorporated Fairfax County, Virginia,...

 introduced in 2003 a line of flavanol-rich chocolate products under the brand name CocoaVia

CocoaVia

-Brand Name Reintroduction:The CocoaVia line of snacks that was introduced in 2003 included snack bars , chocolate covered almonds and chocolate bars was discontinued in the United States in late 2008 or early 2009...

, prepared using their proprietary process called Cocoapro. In 2008, the product was rebranded as Cirku.