Flavonoid biosynthesis

Flavonoids are synthesized by the phenylpropanoid metabolic pathway in which the amino acid phenylalanine is used to produce 4-coumaroyl-CoA. 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.

Biosynthesis of catechin

Flavanoids can possess chiral carbons. Methods of analysis should take this element into account especially regarding bioactivity or enzyme stereospecificity.

Enzymes

The biosynthesis of flavonoids involves several enzymes.

• Anthocyanidin reductase
• Chalcone isomerase
• Dihydrokaempferol 4-reductase
• Flavone synthase
• Flavonoid 3'-monooxygenase
• Flavonol synthase
• Flavanone 3-dioxygenase
• Flavanone 4-reductase
• Leucoanthocyanidin reductase
• Leucocyanidin oxygenase
• Naringenin-chalcone synthase

Methylation

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

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