Flavonols

Backbone of a flavonol, substituent numbers are indicated.

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 the phenolic -OH groups. They are distinct from flavanols (with "a") such as catechin, another class of flavonoids.

Flavonols are present in a wide variety of fruits and vegetables. In Western populations, estimated daily intake is in the range of 20–50 mg per day for flavonols. Individual intake varies depending on the type of diet consumed.^[1]

The phenomenon of dual fluorescence (due to excited state intramolecular proton transfer or ESIPT) is induced by tautomerism of flavonols (and glucosides) and could contribute to plant UV protection and flower colour.^[2]

Flavonols

Flavonols

Name	IUPAC name	5	6	7	8	2'	3'	4'	5'	6'
3-Hydroxyflavone	3-hydroxy-2-phenylchromen-4-one	H	H	H	H	H	H	H	H	H
Azaleatin	2-(3,4-dihydroxyphenyl)-3,7-dihydroxy-5-methoxychromen-4-one	OCH3	H	OH	H	H	H	OH	OH	H
Fisetin	3,3',4',7-tetrahydroxy-2-phenylchromen-4-one	H	H	OH	H	H	H	OH	OH	H
Galangin	3,5,7-trihydroxy-2-phenylchromen-4-one	OH	H	OH	H	H	H	H	H	H
Gossypetin	2-(3,4-dihydroxyphenyl)-3,5,7,8-tetrahydroxychromen-4-one	OH	H	OH	OH	H	OH	OH	H	H
Kaempferide	3,5,7-trihydroxy-2-(4-methoxyphenyl)chromen-4-one	OH	H	OH	H	H	H	OCH3	H	H
Kaempferol	3,4',5,7-tetrahydroxy-2-phenylchromen-4-one	OH	H	OH	H	H	H	OH	H	H
Isorhamnetin	3,5,7-trihydroxy-2-(4-hydroxy-3-methoxyphenyl)chromen-4-one	OH	H	OH	H	H	OCH3	OH	H	H
Morin	2-(2,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one	OH	H	OH	H	OH	H	OH	H	H
Myricetin	3,3',4',5',5,7-hexahydroxy-2-phenylchromen-4-one	OH	H	OH	H	H	OH	OH	OH	H
Natsudaidain	2-(3,4-dimethoxyphenyl)-3-hydroxy-5,6,7,8-tetramethoxychromen-4-one	OCH3	OCH3	OCH3	OCH3	H	H	OCH3	OCH3	H
Pachypodol	5-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-3,7-dimethoxychromen-4-one	OH	H	OCH3	H	H	OCH3	OH	H	H
Quercetin	3,3',4',5,7-pentahydroxy-2-phenylchromen-4-one	OH	H	OH	H	H	OH	OH	H	H
Rhamnazin	3,5-dihydroxy-2-(4-hydroxy-3-methoxyphenyl)-7-methoxychromen-4-one	OH	H	OCH3	H	H	OCH3	OH	H	H
Rhamnetin	2-(3,4-dihydroxyphenyl)-3,5-dihydroxy-7-methoxychromen-4-one	OH	H	OCH3	H	H	OH	OH	H	H

Flavonol glycosides

Flavonols glycosides and acetylated glycosides

Name	Aglycone	3	5	6	7	8	2'	3'	4'	5'	6'
Astragalin	Kaempferol	Glc
Azalein	Azaleatin	Rha
Hyperoside	Quercetin	Gal
Isoquercitin	Quercetin	Glc
Kaempferitrin	Kaempferol	Rha			Rha
Myricitrin	Myricetin	Rha
Quercitrin	Quercetin	Rha
Robinin	Kaempferol	Robinose			Rha
Rutin	Quercetin	Rutinose
Spiraeoside	Quercetin								Glc
Xanthorhamnin	Rhamnetin	trisaccharide
Amurensin	Kaempferol				Glc	tert-amyl
Icariin	Kaempferide	Rha			Glc	tert-amyl
Troxerutin	Quercetin	Rutinose			hydroxyethyl			hydroxyethyl	hydroxyethyl

Drug interactions

Flavonoids have effects on CYP (P450) activity. Flavonols are inhibitor of CYP2C9 ^[3] and CYP3A4,^[1] which are enzymes that metabolize most drugs in the body.

See also

• Phenolic compounds in wine
• Algar-Flynn-Oyamada reaction

References

1. Cermak R, Wolffram S (October 2006). "The potential of flavonoids to influence drug metabolism and pharmacokinetics by local gastrointestinal mechanisms". Curr. Drug Metab. 7 (7): 729–44. doi:10.2174/138920006778520570. PMID 17073577.
2. Tautomerism of flavonol glucosides: relevance to plant UV protection and flower colour, Gerald J. Smith and Kenneth R. Markham. Journal of Photochemistry and Photobiology A: Chemistry, Volume 118, Issue 2, 30 October 1998, Pages 99-105
3. Si D, Wang Y, Zhou YH; et al. (March 2009). "Mechanism of CYP2C9 inhibition by flavones and flavonols". Drug Metab. Dispos. 37 (3): 629–34. doi:10.1124/dmd.108.023416. PMID 19074529.