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).
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.
Catechin and epicatechin are the building blocks of the proanthocyanidins, a type of condensed tannin.
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.
As flavonoids, catechins can act as antioxidants when in high concentration in vitro, but compared with other flavonoids, their antioxidant potential is low. 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.
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.
Catechins and epicatechins are found in cocoa, 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).Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), contains (+)-catechins (67 mg/kg). (-)-Epicatechin and (+)-catechin are among the main natural phenols in argan oil.
The biosynthesis of catechin begins with ma 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
Human metabolites of epicatechin (excluding colonic metabolites)
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.
The stereochemical configuration of catechins has a strong impact on their uptake and metabolism as uptake is highest for (-)-epicatechin and lowest for (-)-catechin.
Inter-species differences in (-)-epicatechin metabolism.
Nanoparticle methods are under preliminary research as potential delivery systems of catechins. Cocoa catechins are under preliminary research for their potential to affect the risk of cardiovascular diseases. One limited meta-analysis showed that increasing consumption of green tea and its catechins to seven cups per day provided a small reduction in prostate cancer.
Epigeoside (Catechin-3-O-alpha-L-rhamnopyranosyl-(1-4)-beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranoside) can be isolated from the rhizomes of Epigynum auritum.
Association between flavan-3-ol intake and incidence of cardiovascular disease in different cohort studies. Data compare the bottom and top quintiles of intake.
Centuries ago, catechin-containing extracts were thought to be useful for treating heart diseases, and an effect on the permeability of capillaries was shown in 1936. Limited evidence from dietary studies indicates that catechins may have an effect on endothelium-dependent vasodilation which could contribute to normal blood flow regulation in humans. Green tea catechins may improve blood pressure, especially when systolic blood pressure is above 130 mmHg. 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.
The European Food Safety Authority established that cocoa flavanols have an effect on vascular function in healthy adults by concluding: "cocoa flavanols help maintain endothelium-dependent vasodilation, which contributes to normal blood flow". Data from observational cohort studies have not shown a consistent association between flavan-3-ol intake and risk of cardiovascuar diseases.
Catechins released into the ground by some plants may hinder the growth of their neighbors, a form of allelopathy.Centaurea maculosa, the spotted knapweed often studied for this behavior, releases catechin isomers into the ground through its roots, potentially having effects as an antibiotic or herbicide. One hypothesis is that it causes a reactive oxygen species wave through the target plant's root to kill root cells by apoptosis. 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 is an invasive, uncontrolled weed.
^Rinaldo D, Batista JM, Rodrigues J, et al. (August 2010). "Determination of catechin diastereomers from the leaves of Byrsonima species using chiral HPLC-PAD-CD". Chirality. 22 (8): 726-33. doi:10.1002/chir.20824. PMID20143413.
^Kríz Z, Koca J, Imberty A, Charlot A, Auzély-Velty R (July 2003). "Investigation of the complexation of (+)-catechin by ?-cyclodextrin by a combination of NMR, microcalorimetry and molecular modeling techniques". Org. Biomol. Chem. 1 (14): 2590-5. doi:10.1039/B302935M. PMID12956082.
^Tournaire C, Croux S, Maurette MT, et al. (August 1993). "Antioxidant activity of flavonoids: Efficiency of singlet oxygen (1?g) quenching". J. Photochem. Photobiol. B, Biol. 19 (3): 205-15. doi:10.1016/1011-1344(93)87086-3. PMID8229463.
^Janeiro, Patricia; Oliveira Brett, Ana Maria (2004). "Catechin electrochemical oxidation mechanisms". Analytica Chimica Acta. 518: 109-115. doi:10.1016/j.aca.2004.05.038.
^Osman, A.M.; Wong, K.K.Y.; Fernyhough, A. (2007). "The laccase/ABTS system oxidizes (+)-catechin to oligomeric products". Enzyme and Microbial Technology. 40 (5): 1272-1279. doi:10.1016/j.enzmictec.2006.09.018.
^Gálvez, Miguel Carrero; Barroso, Carmelo García; Pérez-Bustamante, Juan Antonio (1994). "Analysis of polyphenolic compounds of different vinegar samples". Zeitschrift für Lebensmittel-Untersuchung und -Forschung. 199 (1): 29-31. doi:10.1007/BF01192948.
^Quinde-Axtell, Zory; Baik, Byung-Kee (2006). "Phenolic Compounds of Barley Grain and Their Implication in Food Product Discoloration". J. Agric. Food Chem. 54 (26): 9978-9984. doi:10.1021/jf060974w. PMID17177530.
^Kielhorn, S; Thorngate Iii, J.H (1999). "Oral sensations associated with the flavan-3-ols (+)-catechin and (-)-epicatechin". Food Quality and Preference. 10 (2): 109-116. doi:10.1016/S0950-3293(98)00049-4.
^Rani, Arti; Singh, Kashmir; Ahuja, Paramvir S.; Kumar, Sanjay (2012). "Molecular regulation of catechins biosynthesis in tea [Camellia sinensis (L.) O. Kuntze]". Gene. 495 (2): 205-10. doi:10.1016/j.gene.2011.12.029. PMID22226811.
^Punyasiri, P.A.N.; Abeysinghe, I. S. B.; Kumar, V.; Treutter, D.; Duy, D.; Gosch, C.; Martens, S.; Forkmann, G.; Fischer, T. C. (2004). "Flavonoid biosynthesis in the tea plant Camellia sinensis: Properties of enzymes of the prominent epicatechin and catechin pathways". Archives of Biochemistry and Biophysics. 431 (1): 22-30. doi:10.1016/j.abb.2004.08.003. PMID15464723.
^Skadhauge, Birgitte; Gruber, Margaret Y.; Thomsen, Karl Kristian; Von Wettstein, Diter (April 1997). "Leucocyanidin Reductase Activity and Accumulation of Proanthocyanidins in Developing Legume Tissues". American Journal of Botany. 84 (4): 494-503. doi:10.2307/2446026. JSTOR2446026.
^Maugé C, Granier T, d'Estaintot BL, et al. (April 2010). "Crystal structure and catalytic mechanism of leucoanthocyanidin reductase from Vitis vinifera". J. Mol. Biol. 397 (4): 1079-91. doi:10.1016/j.jmb.2010.02.002. PMID20138891.
^Sambandam, T.; Mahadevan, A. (1993). "Degradation of catechin and purification and partial characterization of catechin oxygenase fromChaetomium cupreum". World Journal of Microbiology & Biotechnology. 9: 37-44. doi:10.1007/BF00656513.
^ abc"Flavonoids". Linus Pauling Institute, Oregon State University, Corvallis. 2016. Retrieved 2016.
^Ottaviani, J. I.; Momma, T. Y.; Heiss, C; Kwik-Uribe, C; Schroeter, H; Keen, C. L. (2011). "The stereochemical configuration of flavanols influences the level and metabolism of flavanols in humans and their biological activity in vivo". Free Radical Biology and Medicine. 50 (2): 237-44. doi:10.1016/j.freeradbiomed.2010.11.005. PMID21074608.
^Ye, J. H; Augustin, M. A (2018). "Nano- and micro-particles for delivery of catechins: Physical and biological performance". Critical Reviews in Food Science and Nutrition: 1-17. doi:10.1080/10408398.2017.1422110. PMID29345975.
^Matsuda M, Otsuka Y, Jin S, et al. (February 2008). "Biotransformation of (+)-catechin into taxifolin by a two-step oxidation: primary stage of (+)-catechin metabolism by a novel (+)-catechin-degrading bacteria, Burkholderia sp. KTC-1, isolated from tropical peat". Biochem. Biophys. Res. Commun. 366 (2): 414-9. doi:10.1016/j.bbrc.2007.11.157. PMID18068670.
^Shibuya H, Agusta A, Ohashi K, Maehara S, Simanjuntak P (July 2005). "Biooxidation of (+)-catechin and (-)-epicatechin into 3,4-dihydroxyflavan derivatives by the endophytic fungus Diaporthe sp. isolated from a tea plant". Chem. Pharm. Bull. 53 (7): 866-7. doi:10.1248/cpb.53.866. PMID15997157.
^Friedrich, Wolfgang; Galensa, Rudolf (2002). "Identification of a new flavanol glucoside from barley ( Hordeum vulgare L.) and malt". European Food Research and Technology. 214 (5): 388-393. doi:10.1007/s00217-002-0498-x.
^Jin QD, Mu QZ (1991). "[Study on glycosidal constituents from Epigynum auritum]". Yao Xue Xue Bao (in Chinese). 26 (11): 841-5. PMID1823978.
^Schroeder, Johann (1655). Pharmacopoeia medico-chymica: sive thesaurus pharmacologeus. Ulmae Suevorum: Johannis Gerlini.
^Berends, KAW (1829). Handbuch der praktischen Arzneiwissenschaft oder der speziellen Pathologie und Therapie. Berlin: Enslin.
^Armentano, L; Bentsáth, A; Béres, T; Rusznyák, St; Szent-Györgyi, A (1936). "Über den Einfluß von Substanzen der Flavongruppe auf die Permeabilität der Kapillaren. Vitamin P". Deutsche Medizinische Wochenschrift. Thieme. 62 (33): 1325-1328. doi:10.1055/s-0028-1141260.
^Ellinger, S; Reusch, A; Stehle, P; Helfrich, H. P. (2012). "Epicatechin ingested via cocoa products reduces blood pressure in humans: A nonlinear regression model with a Bayesian approach". American Journal of Clinical Nutrition. 95 (6): 1365-77. doi:10.3945/ajcn.111.029330. PMID22552030.
^ abKhalesi, S; Sun, J; Buys, N; Jamshidi, A; Nikbakht-Nasrabadi, E; Khosravi-Boroujeni, H (2014). "Green tea catechins and blood pressure: A systematic review and meta-analysis of randomised controlled trials". European Journal of Nutrition. 53 (6): 1299-311. doi:10.1007/s00394-014-0720-1. PMID24861099.
^Martinez SE; Davies NM; Reynolds JK (2013). "Toxicology and Safety of Flavonoids". Methods of Analysis, Preclinical and Clinical Pharmacokinetics, Safety, and Toxicology. John Wiley & Son. p. 257. ISBN978-0-470-57871-1.
^Yamamoto M, Nakatsuka S, Otani H, Kohmoto K, Nishimura S (June 2000). "(+)-catechin acts as an infection-inhibiting factor in strawberry leaf". Phytopathology. 90 (6): 595-600. doi:10.1094/PHYTO.2000.90.6.595. PMID18944538.
^Chen Z, Liang J, Zhang C, Rodrigues CJ (October 2006). "Epicatechin and catechin may prevent coffee berry disease by inhibition of appressorial melanization of Colletotrichum kahawae". Biotechnol. Lett. 28 (20): 1637-40. doi:10.1007/s10529-006-9135-2. PMID16955359.