Catechin

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Catechin
Chemical structure of (+)-Catechin
Identifiers
CAS number 7295-85-4 (±) N, 154-23-4 (+) YesY, 18829-70-4 (-) YesY, 88191-48-4 (+), hydrate YesY
PubChem 9064
ChemSpider 8711 YesY
UNII 8R1V1STN48 YesY
ChEBI CHEBI:15600 YesY
ChEMBL CHEMBL251445 N
Jmol-3D images Image 1
Properties
Molecular formula C15H14O6
Molar mass 290.27 g mol−1
Appearance Colorless solid
Melting point 175 to 177 °C (347 to 351 °F; 448 to 450 K)
λmax 276 nm
Chiral rotation [α]D +14.0°
Hazards
MSDS sciencelab AppliChem
R-phrases R36/37/38
S-phrases S26-S36
Main hazards Mutagenic for mammalian somatic cells, mutagenic for bacteria and/or yeast
LD50 (+)-catechin : 10,000 mg/kg in rat (RTECS)
10,000 mg/kg in mouse
3,890 mg/kg in rat (other source)
Pharmacology
Routes of
administration
Oral
Excretion Urines
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Catechin /ˈkætɨɪn/ is a flavan-3-ol, a type of natural phenol and antioxidant. It is a plant secondary metabolite. It belongs to the group of flavan-3-ols (or simply flavanols), part of the chemical family of flavonoids.

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

Chemistry[edit]

Catechin numbered

Catechin possesses two benzene rings (called the A- and B-rings) and a dihydropyran heterocycle (the C-ring) with a hydroxyl group on carbon 3. The A ring is similar to a resorcinol moiety while the B ring is similar to a catechol moiety. There are two chiral centers on the molecule on carbons 2 and 3. Therefore, it has four diastereoisomers. Two of the isomers are in trans configuration and are called catechin and the other two are in cis configuration and are called epicatechin.

The most common catechin isomer is the (+)-catechin. The other stereoisomer is (-)-catechin or ent-catechin. The most common epicatechin isomer is (-)-epicatechin (also known under the names L-epicatechin, epicatechol, (-)-epicatechol, l-acacatechin, l-epicatechol, epi-catechin, 2,3-cis-epicatechin or (2R,3R)-(-)-epicatechin).

The different epimers can be distinguished using chiral 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 or DL-catechin and (+/-)-epicatechin or DL-epicatechin.

3D view of "pseudoequatorial" (E) conformation of(+)-catechin

Moreover, the flexibility of the C-ring allows for two conformation 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 of A- and E-conformers in aqueous solution and their conformational equilibrium has been evaluated to be 33:67.[3]

Regarding the antioxidant activity, (+)-catechin has been found to be the most powerful scavenger between different members of the different classes of flavonoids. 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.[4]

Catechin exists in the form of a glycoside.[5] Antioxidant properties can also be provided using a catechin associated with a sugar. In 1975-76, a group of USSR scientists of Kaz ssr discovered first the catechin rhamnoside using the plants of Filipendula that grow in that region. Pioneer and head of the discovery was PhD N. D. Storozhenko born in 1944. Though not thoroughly studied, the rhamnoside of catechin can enter the blood cell without breaking the outer layer.

Oxidation[edit]

Electrochemical experiments show that (+)-catechin oxidation mechanism proceeds in sequential steps, related with the catechol and resorcinol 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]

Spectral data[edit]

UV spectrum of catechin.
UV-Vis
Lambda-max: 276 nm
Extinction coefficient (log ε) 4.01
IR
Major absorption bands 1600 cm−1(benzene rings)
NMR
Proton NMR


(500 MHz, CD3OD):
Reference[7]
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

History[edit]

l-Epicatechin can be found in cacao beans and was first called kakaool or cacao-ol.[8] Maximilian Nierenstein was among those who proved the presence of catechin in cocoa beans in 1931.[9]

Natural occurrences[edit]

(+)-Catechin and (-)-epicatechin as well as their gallic acid conjugates are ubiquitous constituents of vascular plants, and frequent components of traditional herbal remedies, such as the Chinese medicine plant Uncaria rhynchophylla and others. The two isomers are mostly associated with cacao and tea constituents, but (+)-catechin is also found in green algae such as Myriophyllum spicatum.[10]

In food[edit]

Catechins and epicatechins are found in cocoa,[11] which, according to one database, has the highest content (108 mg/100 g) of catechins among foods analyzed, followed by prune juice (25 mg/100 ml) and broad bean pod (16 mg/100 g).[12] Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), contains (+)-catechins (67 mg/kg).[13] (-)-Epicatechin and (+)-catechin are among the main natural phenols in argan oil.[14]

Catechins are diverse among foods,[12] from peaches[15] to green tea and vinegar.[12][16] Catechins are found in barley grain where they are the main phenolic compound responsible for dough discoloration.[17]

see also : List of phytochemicals in food, List of micronutrients and List of antioxidants in food

Taste[edit]

The taste associated with monomeric (+)-catechin or (-)-epicatechin is described as not exactly astringent, nor exactly bitter.[18]

Metabolism[edit]

Biosynthesis[edit]

Biosynthesis of 4-hydroxycinnamoyl-CoA.png

The biosynthesis of catechin begins with a 4-hydroxycinnamoyl CoA starter unit which undergoes chain extension by the addition of three malonyl-CoAs through a PKSIII pathway. 4-hydroxycinnamoyl CoA is biosynthesized from L-phenylalanine through the Shikimate pathway. L-phenylalanine is first deaminated by phenylalanine ammonia lyase (PAL) forming cinnamic acid which is then oxidized to 4-hydroxycinnamic acid by cinnamate 4-hydroyxylase. Chalcone synthase then catalyzes the condensation of 4-hydroxycinnamoyl CoA and three molecules of malonyl-CoA to form chalcone. Chalcone is then isomerized to naringenin by chalcone isomerase which is oxidized to eriodictyol by flavonoid 3’- hydroxylase and further oxidized to taxifolin by flavanone 3-hydroxylase. Taxifolin is then reduced by dihydroflavanol 4-reductase and leucoanthocyanidin reductase to yield catechin. The biosynthesis of catechin is shown below[19][20][21]

Leucocyanidin reductase (LCR) uses 2,3-trans-3,4-cis-leucocyanidin to produce (+)-catechin and is the first enzyme in the proanthocyanidins (PA)-specific pathway. Its activity has been measured in leaves, flowers, and seeds of the legumes Medicago sativa, Lotus japonicus, Lotus uliginosus, Hedysarum sulfurescens, and Robinia pseudoacacia.[22] The enzyme is also present in Vitis vinifera (grape).[23]

Biosynthesis of catechin.png

Biodegradation[edit]

Catechin oxygenase, a key enzyme in the degradation of catechin, is present in fungi and bacteria.[24]

Among bacteria, degradation of (+)-catechin can be achieved by Acinetobacter calcoaceticus. Catechin is metabolized to protocatechuic acid (PCA) and phloroglucinol carboxylic acid (PGCA).[25] It is also degraded by Bradyrhizobium japonicum. Phloroglucinol carboxylic acid is further decarboxylated to phloroglucinol, which is dehydroxylated to resorcinol. Resorcinol is hydroxylated to hydroxyquinol. Protocatechuic acid and hydroxyquinol undergo intradiol cleavage through protocatechuate 3,4-dioxygenase and hydroxyquinol 1,2-dioxygenase to form β-carboxy cis, cis-muconic acid and maleyl acetate.[26]

Among fungi, degradation of catechin can be achieved by Chaetomium cupreum.[27]

In rats, all plasma catechin metabolites are present as conjugated forms and mainly constituted by glucuronidated derivatives. In the liver, the concentrations of catechin derivatives are lower than in plasma, and no accumulation is observed when the rats are adapted for 14 days to the supplemented diets. The hepatic metabolites are intensively methylated (90–95%), but in contrast to plasma, some free aglycones can be detected.[28] Rats fed with (+)-catechin and (-)-epicatechin exhibit (+)-catechin 5-O-β-glucuronide and (-)-epicatechin 5-O-β-glucuronide in their body fluids.[29] The primary metabolite of (+)-catechin in plasma is glucuronide in the nonmethylated form. In contrast, the primary metabolites of (-)-epicatechin in plasma are glucuronide and sulfoglucuronide in nonmethylated forms, and sulfate in the 3'-O-methylated forms (3'OMC).[30] Catechin is absorbed into intestinal cells and metabolized extensively because no native catechin can be detected in plasma from the mesenteric vein. Mesenteric plasma contains glucuronide conjugates of catechin and 3'-O-methyl catechin, indicating the intestinal origin of these conjugates. Additional methylation and sulfation occur in the liver, and glucuronide or sulfate conjugates of 3'OMC are excreted extensively in bile. Circulating forms are mainly glucuronide conjugates of catechin and 3'OMC.[31] Another study shows that catechin undergoes enzymatic oxidation by tyrosinase in the presence of glutathione (GSH) to form mono-, bi-, and tri-glutathione conjugates of catechin and mono- and bi-glutathione conjugates of a catechin dimer.[32]

In the crab eating macaque Macaca iris, (+)-catechin administered orally or intraperitonally leads to the formation of 10 metabolites and notably to m-hydroxyphenylhydracrylic acid excreted in the urine.[33]

In man, (+)-catechin absorbed orally is metabolized largely within 24 hours with the production of eleven metabolites detected in the urine.[34]

Biotransformation[edit]

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

The laccase/ABTS system oxidizes (+)-catechin to oligomeric products[36] of which proanthocyanidin A2 is a dimer.

(+)-Catechin and (-)-epicatechin are transformed by the endophytic filamentous fungus Diaporthe 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.[37]

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.[38]

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

Glycosides[edit]

Bioactivity studies[edit]

Catechin is reported to induce longevity in the nematode worm Caenorhabditis elegans.[41] Transcriptomic studies shows that catechin reduces atherosclerotic lesion development in apo E-deficient mice.[42] (+)- and (−)-catechin seem to have stereospecific opposite effects on glycogen metabolism in isolated rat hepatocytes.[43] (+)-Catechin inhibits intestinal tumor formation in mice.[44] (+)-Catechin inhibits the oxidation of low density lipoprotein.[45]
(-)-Catechin suppresses expression of Kruppel-like factor 7[46] and acts as agonist of PPARgamma, nuclear receptor that is current pharmacological target for the treatment of diabetes type 2.[47]
Catechin shows an enhancement of the antifungal effect of amphotericin B against Candida albicans.[48]

Incubation experiments with (+)-catechin show a prevention of human plasma oxidation.[49]

Interactions with human genes[edit]

Catechin interacts the most with the PTGS2, IL1B, CAT, CYP1A1, SOD, BAX, CASP3, MAPK1, MAPK3 and S100B human genes.[50]

PTGS2 (aka COX-2 for cyclooxygenase-2) is a dioxygenase. The presence of catechin seems to increase its expression.
IL1B induces the formation of cyclooxygenase-2 (PTGS2/COX2). Catechin increases its expression.
CAT is a catalase. Catechin decreases its expression.
CYP1A1 (Cytochrome P450, family 1, member A1) is an enzyme implied in the metabolism of xenobiotics. Catechin decreases its expression.
SOD (Superoxide dismutase) is an enzyme that catalyzes the dismutation of superoxide into oxygen and hydrogen peroxide. Catechin increases its expression.
BAX (Bcl-2–associated X protein) is a protein of the Bcl-2 gene family. It promotes apoptosis by competing with Bcl-2 proper. Catechin increases its expression.
CASP3 (Caspase 3) is a protein that plays a central role in the execution-phase of cell apoptosis. Catechin increases its expression.
MAPK1 (Mitogen-activated protein kinase 1) and MAPK3 (Mitogen-activated protein kinase 3) are enzymes that are extracellular signal-regulated kinases (ERKs) and act as an integration point for multiple biochemical signals, involved in a wide variety of cellular processes such as proliferation, differentiation, transcription regulation, and development. Catechin seems to increase their expression.
S100B (S100 calcium binding protein B) is a pro-inflammatory enzyme specific of mature astrocytes that ensheath the blood vessels. Catechin decreases the expression of the gene and could regulate S100B-activated oxidant stress-sensitive pathways through blocking p47phox protein expression. Treatment with catechin could eliminate reactive oxygen species (ROS) to reduce oxidative stress stimulated by S100B. Catechin decreases its expression.

Experiments on human Caco-2 cells show changes in the expression of genes like STAT1, MAPKK1, MRP1 and FTH1 genes, which are involved in the cellular response to oxidative stress, are in agreement with the antioxidant properties of catechin. In addition, the changes in the expression of genes like C/EBPG, topoisomerase 1, MLF2 and XRCC1 suggest novel mechanisms of action at the molecular level.[51]


Detail for all tested genes :
(dec : decreased expression, inc : increased expression, = : does not affect the activity, expression assayed in human if not specified otherwise)[52]
ABCG2 : (-)-catechin decreases the expression of ABCG2
ACE (in Rattus norvegicus) : (+)-catechin or (-)-epicatechin do not affect the activity of the angiotensin-converting enzyme
ACTB (in Rattus norvegicus) decrease
AKT1 decrease
ANXA2 increase
ARHGAP4 decrease
ATF4 increase
BAT2 increase
BAX (rattus norvegicus) increase
BCL2 decrease
BRCC3 decrease
BTG1 increase
CASP3 increase
CAT (mus musculus) decrease
CCL2 increase
CCND1 decrease
CD81 increase
CD9 increase
CEBPG increase
CXCL10 increase
CYP19A1 (rattus norvegicus) increase
CYP1A1 decrease
CYP1A2 =
DEK decrease
DFFA (mus musculus) decrease
DNMT1 decrease
EWSR1 increase
FLT3LG decrease
FTH1 increase
GRN increase
HCFC1 increase
HEAB decrease
HMOX1 increase
HOXD3 increase
HSPD1 decrease
ICAM1 increase
IL10 increase
IL1B increase
IL2RA decrease
IL32 decrease
IRF4 decrease
ITGAL increase
ITGB2 increase
LYN decrease
MAP2K1 decrease ?
MAPK1 increase ?
MAPK3 increase ?
MIF decrease
NCF1 ?
NFE2L2 increase
NFKBIA decrease
NOS2 (mus musculus) increase
NOTCH1 increase
NPM1 decrease
PARP1 (mus musculus) increase
PECAM1 increase
PLAT increase
PLAU increase
PON1 =
PTGS2 increase?
RAC1 decrease
RARB decrease
RELA decrease
RPL6 increase
S100B decrease
SERPINE1 decrease
SF1 decrease
SLC20A1 increase
SOD (Drosophila melanogaster) increase
SOD2 (Drosophila melanogaster) increase
STAT1 decrease
STAT5B increase
STAT6 increase
SULT1A1 increase : sulfation of catechin
TCF7 increase
TK1 decrease
TNF increase
TNFRSF8 decrease
TOP1 decrease
TOP2A decrease
TRP53 increase
XCR1 decrease
ZNF593 increase

Ecological effects[edit]

Catechin also has ecological functions.

It is released into the ground by some plants to hinder the growth of their neighbors, a form of allelopathy.[53] Centaurea maculosa, the spotted knapweed, is the most studied plant showing this behaviour, catechin isomers, both released into the ground through its root exudates, have effects ranging from antibiotic to herbicide. It causes a reactive oxygen species wave through the target plant's root starting in the apical meristem rapidly followed by a Ca2+ spike that kills the root cells through apoptosis.[54] Most plants in the European ecosystem have defenses against catechin, but few plants are protected against it in the North-American ecosystem where Centaurea maculosa has been introduced causing uncontrolled growth of this weed.

(+)-Catechin acts as an infection-inhibiting factor in strawberry leaf.[55] Epicatechin and catechin may prevent coffee berry disease by inhibition of appressorial melanization of Colletotrichum kahawae.[56]

Other uses[edit]

It has been suggested that (+)-catechin could be used as a scavenger for indoor air pollutents such as volatile organic compounds (VOC)[57] to adapt for instance as filters to air conditioners or to air purifiers.

References[edit]

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