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Catechin

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(Redirected fromEpicatechin)
Type of natural phenol as a plant secondary metabolite
Catechin
Chemical structure of (+)-Catechin
Chemical structure of (+)-Catechin
Names
IUPAC name
(2R,3S)-2-(3,4-Dihydroxyphenyl)-3,4-dihydro-2H-chromene-3,5,7-triol
Other names
Cianidanol
Cyanidanol
(+)-catechin
D-Catechin
Catechinic acid
Catechuic acid
Cianidol
Dexcyanidanol
(2R,3S)-Catechin
2,3-trans-Catechin
(2R,3S)-Flavan-3,3′,4′,5,7-pentol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard100.005.297Edit this at Wikidata
EC Number
  • 205-825-1
KEGG
UNII
  • InChI=1S/C15H14O6/c16-8-4-11(18)9-6-13(20)15(21-14(9)5-8)7-1-2-10(17)12(19)3-7/h1-5,13,15-20H,6H2/t13-,15+/m0/s1 checkY
    Key: PFTAWBLQPZVEMU-DZGCQCFKSA-N checkY
  • InChI=1/C15H14O6/c16-8-4-11(18)9-6-13(20)15(21-14(9)5-8)7-1-2-10(17)12(19)3-7/h1-5,13,15-20H,6H2/t13-,15+/m0/s1
    Key: PFTAWBLQPZVEMU-DZGCQCFKBX
  • Oc1ccc(cc1O)[C@H]3Oc2cc(O)cc(O)c2C[C@@H]3O
Properties
C15H14O6
Molar mass290.271 g·mol−1
AppearanceColorless solid
Melting point175 to 177 °C (347 to 351 °F; 448 to 450 K)
UV-vis (λmax)276 nm
+14.0°
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Mutagenic for mammalian somatic cells, mutagenic for bacteria and yeast
GHS labelling:
GHS07: Exclamation mark
Warning
H315,H319,H335
P261,P264,P271,P280,P302+P352,P304+P340,P305+P351+P338,P312,P321,P332+P313,P337+P313,P362,P403+P233,P405,P501
Lethal dose or concentration (LD, LC):
(+)-catechin : 10,000 mg/kg in rat (RTECS)
10,000 mg/kg in mouse
3,890 mg/kg in rat (other source)
Safety data sheet (SDS)sciencelabAppliChem[permanent dead link‍]
Pharmacology
Oral
Pharmacokinetics:
Urines
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Chemical compound

Catechin/ˈkætɪkɪn/ is aflavan-3-ol, a type ofsecondary metabolite providingantioxidant roles inplants. It belongs to the subgroup ofpolyphenols calledflavonoids.

The name of the catechin chemical family derives fromcatechu, which is the tannic juice or boiled extract ofMimosa catechu (Acacia catechu L.f.).[1]

Chemistry

[edit]
Catechin numbered

Catechin possesses twobenzene rings (called the A and B rings) and adihydropyran heterocycle (the C ring) with ahydroxyl group on carbon 3. The A ring is similar to aresorcinol moiety while the B ring is similar to acatechol moiety. There are twochiral centers on the molecule on carbons 2 and 3. Therefore, it has fourdiastereoisomers. Two of the isomers are intrans configuration and are calledcatechin and the other two are incis configuration and are calledepicatechin.

The most common catechin isomer is (+)-catechin. The otherstereoisomer is (−)-catechin orent-catechin. The most common epicatechin isomer is (−)-epicatechin (also known under the namesL-epicatechin, epicatechol, (−)-epicatechol,L-acacatechin,L-epicatechol, epicatechin, 2,3-cis-epicatechin or (2R,3R)-(−)-epicatechin).

The different epimers can be separated usingchiral column chromatography.[2]

Making reference to no particular isomer, the molecule can just be called catechin. Mixtures of the different enantiomers can be called (±)-catechin orDL-catechin and (±)-epicatechin orDL-epicatechin.

Catechin and epicatechin are the building blocks of theproanthocyanidins, a type of condensed tannin.

  • Diastereoisomers gallery
  • (+)-catechin (2R,3S)
    (+)-catechin (2R,3S)
  • (−)-catechin (2S,3R)
    (−)-catechin (2S,3R)
  • (−)-epicatechin (2R,3R)
    (−)-epicatechin (2R,3R)
  • (+)-epicatechin (2S,3S)
    (+)-epicatechin (2S,3S)
3D view of "pseudoequatorial" (E) conformation of (+)-catechin

Moreover, the flexibility of the C-ring allows for twoconformation isomers, putting the B-ring either in a pseudoequatorial position (E conformer) or in a pseudoaxial position (A conformer). Studies confirmed that (+)-catechin adopts a mixture ofA- andE-conformers in aqueous solution and their conformational equilibrium has been evaluated to be 33:67.[3]

As flavonoids, catechins can act asantioxidants when in high concentrationin vitro, but compared with other flavonoids, their antioxidant potential is low.[4] The ability to quench singlet oxygen seems to be in relation with the chemical structure of catechin, with the presence of the catechol moiety on ring B and the presence of a hydroxyl group activating the double bond on ring C.[5]

Oxidation

[edit]

Electrochemical experiments show that (+)-catechin oxidation mechanism proceeds in sequential steps, related with thecatechol andresorcinol groups and the oxidation is pH-dependent. The oxidation of the catechol 3′,4′-dihydroxyl electron-donating groups occurs first, at very low positive potentials, and is a reversible reaction. The hydroxyl groups of the resorcinol moiety oxidised afterwards were shown to undergo an irreversible oxidation reaction.[6]

Thelaccase–ABTS system oxidizes (+)-catechin to oligomeric products[7] of whichproanthocyanidin A2 is a dimer.

Spectral data

[edit]
UV spectrum of catechin.
UV-Vis
Lambda-max:276nm
Extinction coefficient (logε)4.01
IR
Major absorption bands1600 cm−1(benzene rings)
NMR
Proton NMR


(500 MHz, CD3OD):
Reference[8]
d : doublet, dd : doublet of doublets,
m : multiplet, s : singlet

δ :

2.49 (1H, dd, J = 16.0, 8.6 Hz, H-4a),
2.82 (1H, dd, J = 16.0, 1.6 Hz, H-4b),
3.97 (1H, m, H-3),
4.56 (1H, d, J = 7.8 Hz, H-2),
5.86 (1H, d, J = 2.1 Hz, H-6),
5.92 (1H, d, J = 2.1 Hz, H-8),
6.70 (1H, dd, J = 8.1, 1.8 Hz, H-6′),
6.75 (1H, d, J = 8.1 Hz, H-5′),
6.83 (1H, d, J = 1.8 Hz, H-2′)

Carbon-13 NMR
Other NMR data
MS
Masses of
main fragments		ESI-MS [M+H]+m/z : 291.0


273 water loss
139 retro Diels–Alder
123
165
147

Natural occurrences

[edit]

(+)-Catechin and (−)-epicatechin as well as theirgallic acid conjugates are ubiquitous constituents ofvascular plants, and frequent components oftraditional herbal remedies, such asUncaria rhynchophylla. The twoisomers are mostly found ascacao andtea constituents, as well as inVitis vinifera grapes.[9][10][11]

In food

[edit]
Main articles:Phenolic content in tea andPhenolic content in wine

The main dietary sources of catechins in Europe and the United States aretea andpome fruits.[12][13]

Catechins and epicatechins are found incocoa,[14] which, according to one database, has the highest content (108 mg/100 g) of catechins among foods analyzed, followed byprune juice (25 mg/100 ml) andbroad bean pod (16 mg/100 g).[15]Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), contains (+)-catechins (67 mg/kg).[16]

Catechins are diverse among foods,[15] frompeaches[17] togreen tea andvinegar.[15][18] Catechins are found inbarley grain, where they are the main phenolic compound responsible fordough discoloration.[19] The taste associated with monomeric (+)-catechin or (−)-epicatechin is described as slightlyastringent, but not bitter.[20]

Metabolism

[edit]

Biosynthesis

[edit]

The biosynthesis of catechin begins with ma4-hydroxycinnamoyl CoA starter unit which undergoes chain extension by the addition of threemalonyl-CoAs through a PKSIII pathway. 4-Hydroxycinnamoyl CoA is biosynthesized fromL-phenylalanine through the Shikimate pathway.L-Phenylalanine is first deaminated byphenylalanine ammonia lyase (PAL) forming cinnamic acid which is then oxidized to4-hydroxycinnamic acid by cinnamate 4-hydroxylase. Chalcone synthase then catalyzes the condensation of 4-hydroxycinnamoyl CoA and three molecules of malonyl-CoA to formchalcone. Chalcone is then isomerized tonaringenin by chalcone isomerase which is oxidized toeriodictyol by flavonoid 3′-hydroxylase and further oxidized totaxifolin by flavanone 3-hydroxylase. Taxifolin is then reduced by dihydroflavanol 4-reductase andleucoanthocyanidin reductase to yield catechin. The biosynthesis of catechin is shown below[21][22][23]

Leucocyanidin reductase (LCR) uses 2,3-trans-3,4-cis-leucocyanidin to produce (+)-catechin and is the first enzyme in theproanthocyanidin (PA) specific pathway. Its activity has been measured in leaves, flowers, and seeds of the legumesMedicago sativa,Lotus japonicus,Lotus uliginosus,Hedysarum sulfurescens, andRobinia pseudoacacia.[24] The enzyme is also present inVitis vinifera (grape).[25]

Biodegradation

[edit]

Catechin oxygenase, a key enzyme in the degradation of catechin, is present in fungi and bacteria.[26]

Among bacteria, degradation of (+)-catechin can be achieved byAcinetobacter calcoaceticus. Catechin is metabolized toprotocatechuic acid (PCA) andphloroglucinol carboxylic acid (PGCA).[27] It is also degraded byBradyrhizobium japonicum. Phloroglucinol carboxylic acid is furtherdecarboxylated tophloroglucinol, which isdehydroxylated toresorcinol. Resorcinol is hydroxylated tohydroxyquinol. Protocatechuic acid and hydroxyquinol undergointradiol cleavage throughprotocatechuate 3,4-dioxygenase andhydroxyquinol 1,2-dioxygenase to formβ-carboxy-cis,cis-muconic acid andmaleyl acetate.[28]

Among fungi, degradation of catechin can be achieved byChaetomium cupreum.[29]

Metabolism in humans

[edit]
Human metabolites of epicatechin (excluding colonic metabolites)[30]
Schematic representation of (−)-epicatechin metabolism in humans as a function of time post-oral intake. SREM: structurally related (−)-epicatechin metabolites. 5C-RFM: 5-carbon ring fission metabolites. 3/1C-RFM: 3- and 1-carbon-side chain ring fission metabolites. The structures of the most abundant (−)-epicatechin metabolites present in the systemic circulation and in urine are depicted.[30]

Catechins are metabolised upon uptake from thegastrointestinal tract, in particular thejejunum,[31] and in theliver, resulting in so-called structurally related epicatechin metabolites (SREM).[32] The main metabolic pathways for SREMs areglucuronidation,sulfation andmethylation of thecatechol group bycatechol-O-methyl transferase, with only small amounts detected in plasma.[33][30] The majority of dietary catechins are however metabolised by thecolonic microbiome togamma-valerolactones andhippuric acids which undergo furtherbiotransformation,glucuronidation,sulfation andmethylation in theliver.[33]

The stereochemical configuration of catechins has a strong impact on their uptake and metabolism as uptake is highest for (−)-epicatechin and lowest for (−)-catechin.[34]

Biotransformation

[edit]

Biotransformation of (+)-catechin intotaxifolin by a two-step oxidation can be achieved byBurkholderia sp.[35]

(+)-Catechin and (−)-epicatechin are transformed by the endophytic filamentous fungusDiaporthe sp. into the 3,4-cis-dihydroxyflavan derivatives,(+)-(2R,3S,4S)-3,4,5,7,3′,4′-hexahydroxyflavan (leucocyanidin) and(−)-(2R,3R,4R)-3,4,5,7,3′,4′-hexahydroxyflavan, respectively, whereas (−)-catechin and (+)-epicatechin with a (2S)-phenyl group resisted the biooxidation.[36]

Leucoanthocyanidin reductase (LAR) uses (2R,3S)-catechin, NADP+ and H2O to produce 2,3-trans-3,4-cis-leucocyanidin, NADPH, and H+. Its gene expression has been studied in developing grape berries and grapevine leaves.[37]

Glycosides

[edit]

Research

[edit]
Interspecies differences in (−)-epicatechin metabolism.[30]

Vascular function

[edit]

Only limited evidence from dietary studies indicates that catechins may affectendothelium-dependentvasodilation which could contribute to normalblood flow regulation in humans.[40][41] Green tea catechins may improve blood pressure, especially when systolic blood pressure is above 130 mmHg.[42][43]

Due to extensive metabolism during digestion, the fate and activity of catechin metabolites responsible for this effect on blood vessels, as well as the actual mode of action, are unknown.[33][44]

Adverse events

[edit]

Catechin and its metabolites can bind tightly to red blood cells and thereby induce the development ofautoantibodies, resulting inhaemolytic anaemia andrenal failure.[45] This resulted in the withdrawal of the catechin-containing drug Catergen, used to treatviral hepatitis,[46] from market in 1985.[47]

Catechins fromgreen tea can behepatotoxic[48] and theEuropean Food Safety Authority has recommended not to exceed 800 mg per day.[49]

Other

[edit]

One limited meta-analysis showed that increasing consumption of green tea and its catechins to seven cups per day provided a small reduction inprostate cancer.[50]Nanoparticle methods are under preliminary research as potential delivery systems of catechins.[51]

Botanical effects

[edit]

Catechins released into the ground by some plants may hinder the growth of their neighbors, a form ofallelopathy.[52]Centaurea maculosa, the spotted knapweed often studied for this behavior, releases catechinisomers into the ground through its roots, potentially having effects as anantibiotic orherbicide. One hypothesis is that it causes areactive oxygen species wave through the target plant's root to kill root cells byapoptosis.[53] Most plants in the European ecosystem have defenses against catechin, but few plants are protected against it in the North American ecosystem whereCentaurea maculosa is an invasive, uncontrolled weed.[52]

Catechin acts as an infection-inhibiting factor in strawberry leaves.[54] Epicatechin and catechin may prevent coffee berry disease by inhibitingappressorial melanization ofColletotrichum kahawae.[55]

References

[edit]
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Flavan-3-ols and theirglycosides
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O-methylated flavan-3ols
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Gallate esters
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