Flavones (from Latin flavus "yellow") are a class of flavonoids based on the backbone of 2-phenylchromen-4-one (2-phenyl-1-benzopyran-4-one) (as shown in the first image of this article). [1] [2]
Flavones are common in foods, mainly from spices, and some yellow or orange fruits and vegetables. [1] Common flavones include apigenin (4',5,7-trihydroxyflavone), luteolin (3',4',5,7-tetrahydroxyflavone), tangeritin (4',5,6,7,8-pentamethoxyflavone), chrysin (5,7-dihydroxyflavone), and 6-hydroxyflavone. [1]
The estimated daily intake of flavones is about 2 mg per day. [1] Following ingestion and metabolism, flavones, other polyphenols, and their metabolites are absorbed poorly in body organs and are rapidly excreted in the urine, indicating mechanisms influencing their presumed absence of metabolic roles in the body. [1] [3]
Flavones have effects on CYP (P450) activity, [4] [5] which are enzymes that metabolize most drugs in the body.
The biosynthesis of flavones proceeds from the phenylpropanoid pathway, which uses L-phenylalanine as a starting point. [6] Phenylalanine ammonia lyase facilitates the deamination of L-phenylalanine to (E)-cinnamate, [6] which is then oxidized by cinnamate 4-hydroxylase to yield p-Coumaric acid. [7] Coenzyme A is attached to the carboxylate facilitated by 4-Coumarate-CoA ligase, forming (Coumaroyl-CoA). [6] A chalcone synthase then facilitates a series of condensation reactions in the presence of 3 malonyl CoA ending with a ring-forming Claisen condensation yielding a chalcone (naringenin chalcone is shown), [8] which is subsequently isomerized by chalcone isomerase resulting in a flavanone (naringenin is shown). [9] It is at this point that the flavanone can undergo further modifications (such as glycosylation or methylation at the various points of the backbone. The subsequent modified flavanones are then transformed into flavones by flavone synthase, which generates a double bond between the C-2 and C-3 positions (the synthesis of apigenin is shown). [10]
In organic chemistry several methods exist for the synthesis of flavones:
Another method is the dehydrative cyclization of certain 1,3-diaryl diketones. [11]
The Wessely–Moser rearrangement (1930) [12] has been an important tool in structure elucidation of flavonoids. It involves the conversion of 5,7,8-trimethoxyflavone into 5,6,7-trihydroxyflavone on hydrolysis of the methoxy groups to phenol groups. It also has synthetic potential for example: [13]
This rearrangement reaction takes place in several steps: A ring opening to the diketone, B bond rotation with formation of a favorable acetylacetone-like phenyl-ketone interaction and C hydrolysis of two methoxy groups and ring closure.
Name | Structure | R3 | R5 | R6 | R7 | R8 | R2' | R3' | R4' | R5' | R6' |
---|---|---|---|---|---|---|---|---|---|---|---|
Flavone backbone | – | – | – | – | – | – | – | – | – | – | |
Primuletin | – | –OH | – | – | – | – | – | – | – | – | |
Chrysin | – | –OH | – | –OH | – | – | – | – | – | – | |
Tectochrysin | – | –OH | – | –OCH3 | – | – | – | – | – | – | |
Primetin | – | –OH | – | – | –OH | – | – | – | – | – | |
Apigenin | – | –OH | – | –OH | – | – | – | –OH | – | – | |
Acacetin | – | –OH | – | –OH | – | – | – | –OCH3 | – | – | |
Genkwanin | – | –OH | – | –OCH3 | – | – | – | –OH | – | – | |
Echioidinin | – | –OH | – | –OCH3 | – | –OH | – | – | – | – | |
Baicalein | – | –OH | –OH | –OH | – | – | – | – | – | – | |
Oroxylin A | – | –OH | –OCH3 | –OH | – | – | – | – | – | – | |
Negletein | – | –OH | –OH | –OCH3 | – | – | – | – | – | – | |
Norwogonin | – | –OH | – | –OH | –OH | – | – | – | – | – | |
Wogonin | – | –OH | – | –OH | –OCH3 | – | – | – | – | – | |
Liquiritigenin [15] | – | – | – | –OH | – | – | – | –OH | – | – | |
Naringenin [15] | – | –OH | – | –OH | – | – | – | –OH | – | – | |
Geraldone | – | – | – | –OH | – | – | –OCH3 | –OH | – | – | |
Tithonine | – | – | – | –OCH3 | – | – | –OH | –OCH3 | – | – | |
Luteolin | – | –OH | – | –OH | – | – | –OH | –OH | – | – | |
6-Hydroxyluteolin | – | –OH | –OH | –OH | – | – | –OH | –OH | – | – | |
Chrysoeriol | – | –OH | – | –OH | – | – | –OCH3 | –OH | – | – | |
Diosmetin | – | –OH | – | –OH | – | – | –OH | –OCH3 | – | – | |
Pilloin | – | –OH | – | –OCH3 | – | – | –OH | –OCH3 | – | – | |
Velutin | – | –OH | – | –OCH3 | – | – | –OCH3 | –OH | – | – | |
Norartocarpetin | – | –OH | – | –OH | – | –OH | – | –OH | – | – | |
Artocarpetin | – | –OH | – | –OCH3 | – | –OH | – | –OH | – | – | |
Scutellarein | – | –OH | –OH | –OH | – | – | – | –OH | – | – | |
Hispidulin | – | –OH | –OCH3 | –OH | – | – | – | –OH | – | – | |
Sorbifolin | – | –OH | –OH | –OCH3 | – | – | – | –OH | – | – | |
Pectolinarigenin | – | –OH | –OCH3 | –OH | – | – | – | –OCH3 | – | – | |
Cirsimaritin | – | –OH | –OCH3 | –OCH3 | – | – | – | –OH | – | – | |
Mikanin | – | –OH | –OCH3 | –OCH3 | – | – | – | –OCH3 | – | – | |
Isoscutellarein | – | –OH | – | –OH | –OH | – | – | –OH | – | – | |
Zapotinin | – | –OH | –OCH3 | – | – | –OCH3 | – | – | – | –OCH3 | |
Zapotin | – | –OCH3 | –OCH3 | – | – | –OCH3 | – | – | – | –OCH3 | |
Cerrosillin | – | –OCH3 | –OCH3 | – | – | – | –OCH3 | – | –OCH3 | – | |
Alnetin | – | –OH | –OCH3 | –OCH3 | –OCH3 | – | – | – | – | – | |
Tricetin | – | –OH | – | –OH | – | – | –OH | –OH | –OH | – | |
Tricin | – | –OH | – | –OH | – | – | –OCH3 | –OH | –OCH3 | – | |
Corymbosin | – | –OH | – | –OCH3 | – | – | –OCH3 | –OCH3 | –OCH3 | – | |
Nepetin | – | –OH | –OCH3 | –OH | – | – | –OH | –OH | – | – | |
Pedalitin | – | –OH | –OH | –OCH3 | – | – | –OH | –OH | – | – | |
Nodifloretin | – | –OH | –OH | –OH | – | – | –OCH3 | –OH | – | – | |
Jaceosidin | – | –OH | –OCH3 | –OH | – | – | –OCH3 | –OH | – | – | |
Cirsiliol | – | –OH | –OCH3 | –OCH3 | – | – | –OH | –OH | – | – | |
Eupatilin | – | –OH | –OCH3 | –OH | – | – | –OCH3 | –OCH3 | – | – | |
Cirsilineol | – | –OH | –OCH3 | –OCH3 | – | – | –OCH3 | –OH | – | – | |
Eupatorin | – | –OH | –OCH3 | –OCH3 | – | – | – | –OCH3 | –OH | – | |
Sinensetin | – | –OCH3 | –OCH3 | –OCH3 | – | – | – | –OCH3 | –OCH3 | – | |
Hypolaetin | – | –OH | – | –OH | –OH | – | –OH | –OH | – | – | |
Onopordin | – | –OH | – | –OH | –OCH3 | – | –OH | –OH | – | – | |
Wightin | – | –OH | – | –OCH3 | –OCH3 | –OCH3 | –OH | – | – | – | |
Nevadensin | – | –OH | –OCH3 | –OH | –OCH3 | – | – | –OCH3 | – | – | |
Xanthomicrol | – | –OH | –OCH3 | –OCH3 | –OCH3 | – | – | –OH | – | – | |
Tangeretin | – | –OCH3 | –OCH3 | –OCH3 | –OCH3 | – | – | –OCH3 | – | – | |
Serpyllin | – | –OH | – | –OCH3 | –OCH3 | –OCH3 | –OCH3 | –OCH3 | – | – | |
Sudachitin | – | –OH | –OCH3 | –OH | –OCH3 | – | –OCH3 | –OH | – | – | |
Acerosin | – | –OH | –OCH3 | –OH | –OCH3 | – | –OH | –OCH3 | – | – | |
Hymenoxin | – | –OH | –OCH3 | –OH | –OCH3 | – | –OCH3 | –OCH3 | – | – | |
Gardenin D | – | –OH | –OCH3 | –OCH3 | –OCH3 | – | –OH | –OCH3 | – | – | |
Nobiletin | – | – | –OCH3 | –OCH3 | –OCH3 | –OCH3 | – | –OCH3 | –OCH3 | – | – |
Scaposin | – | – | –OH | –OCH3 | –OH | –OCH3 | – | –OCH3 | –OCH3 | –OH | |
Name | Structure | R3 | R5 | R6 | R7 | R8 | R2' | R3' | R4' | R5' | R6' |
In one preliminary 2021 study, flavone intake was associated with lower odds of subjective cognitive decline after adjustment for age, total energy intake, major nondietary factors, and specific dietary factors. [16]
Flavonoids are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.
Isoflavones are substituted derivatives of isoflavone, a type of naturally occurring isoflavonoids, many of which act as phytoestrogens in mammals. Isoflavones are produced almost exclusively by the members of the bean family, Fabaceae (Leguminosae).
Naringenin is a flavanone from the flavonoid group of polyphenols. It is commonly found in citrus fruits, especially as the predominant flavonone in grapefruit.
Rutin is the glycoside combining the flavonol quercetin and the disaccharide rutinose. It is a flavonoid glycoside found in a wide variety of plants, including citrus.
Cyanidin is a natural organic compound. It is a particular type of anthocyanidin. It is a pigment found in many red berries including grapes, bilberry, blackberry, blueberry, cherry, chokeberry, cranberry, elderberry, hawthorn, loganberry, açai berry and raspberry. It can also be found in other fruits such as apples and plums, and in red cabbage and red onion. It has a characteristic reddish-purple color, though this can change with pH; solutions of the compound are red at pH < 3, violet at pH 7-8, and blue at pH > 11. In certain fruits, the highest concentrations of cyanidin are found in the seeds and skin. Cyanidin has been found to be a potent sirtuin 6 (SIRT6) activator.
Hesperidin is a flavanone glycoside found in citrus fruits. Its aglycone is hesperetin. Its name is derived from the word "hesperidium", for fruit produced by citrus trees.
Apigenin (4′,5,7-trihydroxyflavone), found in many plants, is a natural product belonging to the flavone class that is the aglycone of several naturally occurring glycosides. It is a yellow crystalline solid that has been used to dye wool.
Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. Kaempferol is a yellow crystalline solid with a melting point of 276–278 °C (529–532 °F). It is slightly soluble in water and highly soluble in hot ethanol, ethers, and DMSO. Kaempferol is named for 17th-century German naturalist Engelbert Kaempfer.
The phenylpropanoids are a diverse family of organic compounds that are biosynthesized by plants from the amino acids phenylalanine and tyrosine in the shikimic acid pathway. Their name is derived from the six-carbon, aromatic phenyl group and the three-carbon propene tail of coumaric acid, which is the central intermediate in phenylpropanoid biosynthesis. From 4-coumaroyl-CoA emanates the biosynthesis of myriad natural products including lignols, flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and phenylpropanoids. The coumaroyl component is produced from cinnamic acid.
Daidzein is a naturally occurring compound found exclusively in soybeans and other legumes and structurally belongs to a class of compounds known as isoflavones. Daidzein and other isoflavones are produced in plants through the phenylpropanoid pathway of secondary metabolism and are used as signal carriers, and defense responses to pathogenic attacks. In humans, recent research has shown the viability of using daidzein in medicine for menopausal relief, osteoporosis, blood cholesterol, and lowering the risk of some hormone-related cancers, and heart disease. Despite the known health benefits, the use of both puerarin and daidzein is limited by their poor bioavailability and low water solubility.
The flavanones, a type of flavonoids, are various aromatic, colorless ketones derived from flavone that often occur in plants as glycosides.
Chalcone synthase or naringenin-chalcone synthase (CHS) is an enzyme ubiquitous to higher plants and belongs to a family of polyketide synthase enzymes (PKS) known as type III PKS. Type III PKSs are associated with the production of chalcones, a class of organic compounds found mainly in plants as natural defense mechanisms and as synthetic intermediates. CHS was the first type III PKS to be discovered. It is the first committed enzyme in flavonoid biosynthesis. The enzyme catalyzes the conversion of 4-coumaroyl-CoA and malonyl-CoA to naringenin chalcone.
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.
Tricin is a chemical compound. It is an O-methylated flavone, a type of flavonoid. It can be found in rice bran and sugarcane.
Fisetin (7,3′,4′-flavon-3-ol) is a plant flavonol from the flavonoid group of polyphenols. It can be found in many plants, where it serves as a yellow/ochre colouring agent. It is also found in many fruits and vegetables, such as strawberries, apples, persimmons, onions and cucumbers. Its chemical formula was first described by Austrian chemist Josef Herzig in 1891.
An aurone is a heterocyclic chemical compound, which is a type of flavonoid. There are two isomers of the molecule, with (E)- and (Z)-configurations. The molecule contains a benzofuran element associated with a benzylidene linked in position 2. In aurone, a chalcone-like group is closed into a 5-membered ring instead of the 6-membered ring more typical of flavonoids.
Coumaroyl-coenzyme A is the thioester of coenzyme-A and coumaric acid. Coumaroyl-coenzyme A is a central intermediate in the biosynthesis of myriad natural products found in plants. These products include lignols, flavonoids, isoflavonoids, coumarins, aurones, stilbenes, catechin, and other phenylpropanoids.
Xanthohumol is a natural product found in the female inflorescences of Humulus lupulus, also known as hops. This compound is also found in beer and belongs to a class of compounds that contribute to the bitterness and flavor of hops. Xanthohumol is a prenylated chalconoid, biosynthesized by a type III polyketide synthase (PKS) and subsequent modifying enzymes.
Chalconoids, also known as chalcones, are natural phenols derived from chalcone. They form the central core for a variety of important biological compounds.
The biosynthesis of phenylpropanoids involves a number of enzymes.