Flavonoid biosynthesis
Flavonoids are synthesized by the phenylpropanoid metabolic pathway in which the amino acid phenylalanine is used to produce 4-coumaroyl-CoA.[1] 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. 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 various polyphenolics.
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Flavanoids can possess chiral carbons. Methods of analysis should take this element into account[2] especially regarding bioactivity or enzyme stereospecificity.[3]
Enzymes
The biosynthesis of flavonoids involves several enzymes.
Backbone
- 4-oumaroyl-CoA Template:Underoverset chalcone (naringenin-chalcone)
- Naringenin-chalcone Template:Underoverset flavanone (naringenin).
Path to cyanidin:
- flavanone Template:Underoverset 3'-hydroxyflavonoid (eriodictyol)
- eriodictyol Template:Underoverset dihydroflavonol (taxifolin)
- taxifolin Template:Underoverset leucocyanidin
- leucocyanidin Template:Underoverset cyanidin
Path to (–)-epicatechin:
Path to (+)-catechin:
Path to flavones:
Path to flavonols:
Path to 3-deoxyanthocyanidins:
- flavanone Template:Underoverset flavan-4-ol
- (Process analogous to taxifolin → cyanidin follows)
Methylation
Glycosylation
- Anthocyanidin 3-O-glucosyltransferase
- Flavone 7-O-beta-glucosyltransferase
- Flavone apiosyltransferase
- Flavonol-3-O-glucoside L-rhamnosyltransferase
- Flavonol 3-O-glucosyltransferase
Further acetylations
References
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