Flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

s are synthesized by the phenylpropanoid metabolic pathway in which the

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the chemical formula, formula . It can be viewed as a benzyl group substituent, substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of ...

is used to produce 4-coumaroyl-CoA. This can be combined with

malonyl-CoA Malonyl-CoA is a coenzyme A derivative of malonic acid. Biosynthesis Malonyl-CoA cannot cross membranes and there is no known malonyl-CoA import mechanism. The biosynthesis therefore takes place locally: * cytosol: Malonyl-CoA is formed by c ...

to yield the true backbone of flavonoids, a group of compounds called chalcones, which contain two

phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula , and is often represented by the symbol Ph (archaically φ) or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ...

rings. Conjugate ring-closure of chalcones results in the familiar form of flavonoids, the three-ringed structure of a

flavone Flavone is an organic compound with the formula . A white solid, flavone is a derivative of chromone with a phenyl (Ph) substituent adjacent to the ether group. The compound is of little direct practical importance, but substituted derivatives, ...

. The metabolic pathway continues through a series of enzymatic modifications to yield

flavanone The flavanones, a type of flavonoids, are various aromatic, colorless ketones derived from flavone that often occur in plants as glycosides. List of flavanones * Blumeatin * Butin * Dichamanetin * Eriodictyol * Hesperetin * Hesperidin * Hom ...

s →

dihydroflavonol The flavanonols (with two "o"s a.k.a. 3-hydroxyflavanone or 2,3-dihydroflavonol) are a class of flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic second ...

s →

anthocyanin Anthocyanins (), also called anthocyans, are solubility, water-soluble vacuole, vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart named a chemical compou ...

s. Along this pathway, many products can be formed, including the

flavonol Flavonols are a class of flavonoids that have the 3-hydroxyflavone backbone (IUPAC name: 3-hydroxy-2-phenylchromen-4-one). Their diversity stems from the different positions of the phenolic –OH groups. They are distinct from flavanols (with ...

flavan-3-ol Flavan-3-ols (sometimes referred to as flavanols) are a subgroup of flavonoids. They are derivatives of flavans that possess a 2-phenyl-3,4-dihydro-2''H''-chromen-3-ol skeleton. Flavan-3-ols are structurally diverse and include a range of compo ...

proanthocyanidin Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex ...

s (tannins) and a host of other various polyphenolics.

Flavanoids can possess

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

carbons. Methods of analysis should take this element into account especially regarding

bioactivity In pharmacology, biological activity or pharmacological activity describes the beneficial or adverse effects of a drug on living matter. When a drug is a complex chemical mixture, this activity is exerted by the substance's active ingredient or ...

or enzyme stereospecificity.

Enzymes

The

biosynthesis Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthe ...

flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

s involves several

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s. * Anthocyanidin reductase *

Chalcone isomerase In enzymology, a chalcone isomerase () is an enzyme that catalyzes the chemical reaction :a chalcone \rightleftharpoons a flavanone Hence, this enzyme has one substrate, a chalcone, and one product, a flavanone. This enzyme belongs to the fam ...

* Dihydrokaempferol 4-reductase * Flavone synthase * Flavonoid 3'-monooxygenase *

Flavonol synthase In enzymology, a flavonol synthase () is an enzyme that catalyzes the following chemical reaction : dihydroflavonol + 2-oxoglutarate + \rightleftharpoons a flavonol + succinate + C + H2O The 3 substrates of this enzyme are dihydroflavonol, 2- ...

Flavanone 3-dioxygenase In enzymology, a flavanone 3-dioxygenase () is an enzyme that catalyzes the chemical reaction :a flavanone + 2-oxoglutarate + O2 \rightleftharpoons a dihydroflavonol + succinate + CO2 The 3 substrates of this enzyme are flavanone, 2-oxoglutara ...

Flavanone 4-reductase In enzymology, a flavanone 4-reductase () is an enzyme that catalysis, catalyzes the chemical reaction :(2S)-flavan-4-ol + NADP+ \rightleftharpoons (2S)-flavanone + NADPH + H+ Thus, the two substrate (biochemistry), substrates of this enzyme are ...

* Leucoanthocyanidin reductase * Leucocyanidin oxygenase * Naringenin-chalcone synthase

Methylation

Apigenin 4'-O-methyltransferase In enzymology, an apigenin 4'-O-methyltransferase () is an enzyme that catalyzes the chemical reaction :S-adenosyl-L-methionine + 5,7,4'-trihydroxyflavone \rightleftharpoons S-adenosyl-L-homocysteine + 4'-methoxy-5,7-dihydroxyflavone Thus, the tw ...

* Luteolin O-methyltransferase *

Quercetin 3-O-methyltransferase In enzymology, a quercetin 3-O-methyltransferase () is an enzyme that catalyzes the chemical reaction :S-adenosyl-L-methionine + 3,5,7,3',4'-pentahydroxyflavone \rightleftharpoons S-adenosyl-L-homocysteine + 3-methoxy-5,7,3',4'-tetrahydroxyflavone ...

Glycosylation

* Anthocyanidin 3-O-glucosyltransferase * Flavone 7-O-beta-glucosyltransferase * Flavone apiosyltransferase * Flavonol-3-O-glucoside L-rhamnosyltransferase * Flavonol 3-O-glucosyltransferase

Further acetylations

* Isoflavone-7-O-beta-glucoside 6"-O-malonyltransferase

References

{{Flavonoids Flavonoids metabolism Biosynthesis