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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.

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

References

1. Ververidis Filippos, F; Trantas Emmanouil; Douglas Carl; Vollmer Guenter; Kretzschmar Georg; Panopoulos Nickolas (October 2007). "Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part I: Chemical diversity, impacts on plant biology and human health". Biotechnology Journal. 2 (10): 1214–34. doi:10.1002/biot.200700084. PMID 17935117.
2. Yáñez, Jaime A.; Andrews, Preston K.; Davies, Neal M. (April 2007). "Methods of analysis and separation of chiral flavonoids". Journal of Chromatography B. 848 (2): 159–181. doi:10.1016/j.jchromb.2006.10.052. PMID 17113835.
3. Trouillas, Patrick; Fagnère, Catherine; Lazzaroni, Roberto; Calliste, Claude; Marfak, Abdelghafour; Duroux, Jean-Luc (December 2004). "A theoretical study of the conformational behavior and electronic structure of taxifolin correlated with the free radical-scavenging activity". Food Chemistry. 88 (4): 571–582. doi:10.1016/j.foodchem.2004.02.009.

• Flavonoids metabolism
• Biosynthesis