XIV

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.

Flavonoid Biosynthesis Diagrams

Biosynthesis of catechin

A biochemical diagram showing the class of flavonoids. And their source in nature through various inter-related plant species.

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

References※