Flavonoids 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 hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

phenylalanine is used to produce

4-coumaroyl-CoA Coumaroyl-coenzyme A is the thioester of coenzyme-A and coumaric acid. Coumaroyl-coenzyme A is a central intermediate in the biosynthesis of myriad natural products found in plants. These products include lignols (precursors to lignin and lign ...

. This can be combined with malonyl-CoA 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 C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen ...

rings. 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

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 * Eriodictyol * Hesperetin * Hesperidin * Homoeriodictyol * ...

s →

dihydroflavonol The flavanonols (with two "o"s a.k.a. 3-hydroxyflavanone or 2,3-dihydroflavonol) are a class of flavonoids that use the 3-hydroxy-2,3-dihydro-2-phenylchromen-4-one (IUPAC name) backbone. Some examples include: * Taxifolin (or Dihydroquercetin) * ...

s → anthocyanins. 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 comp ...

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 compl ...

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 (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from i ...

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 In chemistry, stereospecificity is the property of a reaction mechanism that leads to different stereoisomeric reaction products from different stereoisomeric reactants, or which operates on only one (or a subset) of the stereoisomers."Overlap Co ...

.A theoretical study of the conformational behavior and electronic structure of taxifolin correlated with the free radical-scavenging activity. Patrick Trouillas, Catherine Fagnère, Roberto Lazzaroni, Claude Calliste, Abdelghafour Marfak and Jean-Luc Duroux, Food Chemistry, Volume 88, Issue 4, December 2004, Pages 571-582
/ref>

Enzymes

The biosynthesis of flavonoids involves several

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s. *

Anthocyanidin reductase In enzymology, an anthocyanidin reductase () is an enzyme that catalyzes the chemical reaction :a flavan-3-ol + 2 NAD(P)+ \rightleftharpoons an anthocyanidin + 2 NAD(P)H + H+ The 3 substrates of this enzyme are flavan-3-ol, NAD+, and NADP+, ...

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 ...

* Dihydrokaempferol 4-reductase *

Flavone synthase In enzymology, a flavone synthase () is an enzyme that catalyzes the chemical reaction :a flavanone + 2-oxoglutarate + O2 \rightleftharpoons a flavone + succinate + CO2 + H2O The 3 substrates of this enzyme are flavanone, 2-oxoglutarate, and ...

Flavonoid 3'-monooxygenase In enzymology, a flavonoid 3'-monooxygenase (, was wrongly classified as in the past) is an enzyme that catalyzes the chemical reaction :a flavonoid + NADPH + H+ + O2 \rightleftharpoons a 3'-hydroxyflavonoid + NADP+ + H2O The 4 substrates of ...

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, ...

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-oxoglutar ...

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

* Leucoanthocyanidin reductase *

Leucocyanidin oxygenase In enzymology, a leucocyanidin oxygenase () is an enzyme that catalyzes the chemical reaction :leucocyanidin + 2-oxoglutarate + O2 \rightleftharpoons cis- and trans-dihydroquercetins + succinate + CO2 + 2 H2O The 3 substrates of this enzyme are ...

Naringenin-chalcone synthase Chalcone synthase or naringenin-chalcone synthase (CHS) is an enzyme ubiquitous to higher plants and belongs to a family of polyketide synthase enzymes (PKS) known as type III PKS. Type III PKSs are associated with the production of chalcones, a ...

Methylation

* Apigenin 4'-O-methyltransferase * Luteolin O-methyltransferase * Quercetin 3-O-methyltransferase

Glycosylation

* Anthocyanidin 3-O-glucosyltransferase *

Flavone 7-O-beta-glucosyltransferase In enzymology, a flavone 7-O-beta-glucosyltransferase () is an enzyme that catalyzes the chemical reaction :UDP-glucose + 5,7,3',4'-tetrahydroxyflavone \rightleftharpoons UDP + 7-O-beta-D-glucosyl-5,7,3',4'-tetrahydroxyflavone Thus, the two sub ...

* Flavone apiosyltransferase * Flavonol-3-O-glucoside L-rhamnosyltransferase * Flavonol 3-O-glucosyltransferase

Further acetylations

Isoflavone-7-O-beta-glucoside 6"-O-malonyltransferase In enzymology, an isoflavone-7-O-beta-glucoside 6"-O-malonyltransferase () is an enzyme that catalyzes the chemical reaction :malonyl-CoA + biochanin A 7-O-beta-D-glucoside \rightleftharpoons CoA + biochanin A 7-O-(6-O-malonyl-beta-D-glucoside) ...

References

{{Flavonoids Flavonoids metabolism Biosynthesis