Editing Catechin (section)

== Chemistry ==
[[File:Catechin numbered.svg|thumb|left|Catechin numbered]]
Catechin possesses two [[benzene ring]]s (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 [[chirality (chemistry)|chiral]] centers on the molecule on carbons 2 and 3. Therefore, it has four [[diastereoisomer]]s. Two of the isomers are in [[trans configuration|''trans'' configuration]] and are called ''catechin'' and the other two are in [[cis configuration|''cis'' configuration]] and are called ''epicatechin''.

The most common catechin isomer is (+)-catechin. The other [[stereoisomer]] is (−)-catechin or ''ent''-catechin. The most common epicatechin isomer is (−)-epicatechin (also known under the names <small>L</small>-epicatechin, epicatechol, (−)-epicatechol, <small>L</small>-acacatechin, <small>L</small>-epicatechol, epicatechin, 2,3-''cis''-epicatechin or (2''R'',3''R'')-(−)-epicatechin).

The different epimers can be separated using [[chiral column chromatography]].<ref>{{cite journal | vauthors = Rinaldo D, Batista JM, Rodrigues J, Benfatti AC, Rodrigues CM, dos Santos LC, Furlan M, Vilegas W | display-authors = 6 | title = Determination of catechin diastereomers from the leaves of ''Byrsonima'' species using chiral HPLC-PAD-CD | journal = Chirality | volume = 22 | issue = 8 | pages = 726–733 | date = August 2010 | pmid = 20143413 | doi = 10.1002/chir.20824 }}</ref>

Making reference to no particular isomer, the molecule can just be called catechin. Mixtures of the different enantiomers can be called (±)-catechin or <small>DL</small>-catechin and (±)-epicatechin or <small>DL</small>-epicatechin.

Catechin and epicatechin are the building blocks of the [[proanthocyanidin]]s, a type of condensed tannin.

<gallery caption="Diastereoisomers gallery" widths="200px" heights="120px" perrow="2">
File:(+)-Catechin.png|(+)-catechin (2''R'',3''S'')
File:Catechin.png|(−)-catechin (2''S'',3''R'')
File:(-)-Epicatechin.svg|(−)-epicatechin (2''R'',3''R'')
File:(+)-epicatechin.svg|(+)-epicatechin (2''S'',3''S'')
</gallery>

[[File:Catechin above.PNG|thumb|left|3D view of "pseudoequatorial" (''E'') conformation of (+)-catechin]]
Moreover, the flexibility of the C-ring allows for two [[Conformational isomerism|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.<ref name="Kriz">{{cite journal | vauthors = Kríz Z, Koca J, Imberty A, Charlot A, Auzély-Velty R | title = Investigation of the complexation of (+)-catechin by beta-cyclodextrin by a combination of NMR, microcalorimetry and molecular modeling techniques | journal = Organic & Biomolecular Chemistry | volume = 1 | issue = 14 | pages = 2590–2595 | date = July 2003 | pmid = 12956082 | doi = 10.1039/B302935M }}</ref>

As flavonoids, catechins can act as [[antioxidants]] when in high concentration ''in vitro'', but compared with other flavonoids, their antioxidant potential is low.<ref>{{cite journal | vauthors = Pietta PG | title = Flavonoids as antioxidants | journal = Journal of Natural Products | volume = 63 | issue = 7 | pages = 1035–1042 | date = July 2000 | pmid = 10924197 | doi = 10.1021/np9904509 | s2cid = 23310671 }}</ref> 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.<ref>{{cite journal | vauthors = Tournaire C, Croux S, Maurette MT, Beck I, Hocquaux M, Braun AM, Oliveros E | title = Antioxidant activity of flavonoids: efficiency of singlet oxygen (<sup>1</sup>Δ<sub>''g''</sub>) quenching | journal = Journal of Photochemistry and Photobiology. B, Biology | volume = 19 | issue = 3 | pages = 205–215 | date = August 1993 | pmid = 8229463 | doi = 10.1016/1011-1344(93)87086-3 }}</ref>

===Oxidation===
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.<ref>{{cite journal |doi=10.1016/j.aca.2004.05.038 |title=Catechin electrochemical oxidation mechanisms |year=2004 | vauthors = Janeiro P, Oliveira Brett AM |journal=Analytica Chimica Acta |volume=518 |issue=1–2 |pages=109–115|bibcode=2004AcAC..518..109J |hdl=10316/5128 |hdl-access=free }}</ref>

The [[laccase]]–[[ABTS]] system oxidizes (+)-catechin to oligomeric products<ref>{{cite journal |doi=10.1016/j.enzmictec.2006.09.018 |title=The laccase/ABTS system oxidizes (+)-catechin to oligomeric products | date = April 2007 | vauthors = Osman AM, Wong KK, Fernyhough A |journal=Enzyme and Microbial Technology |volume=40 |issue=5 |pages=1272–1279}}</ref> of which [[proanthocyanidin A2]] is a dimer.

=== Spectral data ===
[[File:Spectre UV-vis catechine.PNG|thumb|right|UV spectrum of catechin.]]
{| border="1" cellspacing="0" cellpadding="3" style="margin: 0 0 0 0.5em; background: #FFFFFF; border-collapse: collapse; border-color: #C0C090;"

! {{Chemical datatable header}} | [[UV/VIS spectroscopy|UV-Vis]]
|-
| [[Lambda-max]]:
| 276 [[Nanometre|nm]]
|-
| [[molar absorptivity|Extinction coefficient]] (log ''ε'')
| 4.01<!-- [α]<sub>D</sub> (22&nbsp;°C) : +14.0° (c 0.4, Me<sub>2</sub>CO) -->
|-

! {{Chemical datatable header}} | [[Infrared|IR]]
|-
| Major absorption bands
| 1600&nbsp;cm<sup>−1</sup>(benzene rings)
|-

! {{Chemical datatable header}} | [[NMR Spectroscopy|NMR]]
|-
| [[Proton NMR]]
<br/>(500&nbsp;MHz, CD3OD): <!-- Link to image of spectrum -->
<br/>Reference<ref>{{cite journal | vauthors = Lin YP, Chen TY, Tseng HW, Lee MH, Chen ST | title = Neural cell protective compounds isolated from ''Phoenix hanceana'' var. ''formosana'' | journal = Phytochemistry | volume = 70 | issue = 9 | pages = 1173–1181 | date = June 2009 | pmid = 19628235 | doi = 10.1016/j.phytochem.2009.06.006 | bibcode = 2009PChem..70.1173L | s2cid = 28636157 }}</ref>
<br/>d : doublet, dd : doublet of doublets,
<br/>m : multiplet, s : singlet
|''[[Chemical shift|δ]]'' :<br/>
2.49 (1H, dd, J = 16.0, 8.6&nbsp;Hz, H-4a),<br/>
2.82 (1H, dd, J = 16.0, 1.6&nbsp;Hz, H-4b), <br/>
3.97 (1H, m, H-3), <br/>
4.56 (1H, d, J = 7.8&nbsp;Hz, H-2),<br/>
5.86 (1H, d, J = 2.1&nbsp;Hz, H-6), <br/>
5.92 (1H, d, J = 2.1&nbsp;Hz, H-8), <br/>
6.70 (1H, dd, J = 8.1, 1.8&nbsp;Hz, H-6′), <br/>
6.75 (1H, d, J = 8.1&nbsp;Hz, H-5′), <br/>
6.83 (1H, d, J = 1.8&nbsp;Hz, H-2′)<br/>
|-
| [[Carbon-13 NMR]] <!-- Link to image of spectrum -->
|-
| Other NMR data <!-- Insert special data e.g. <sup>19</sup>F chem. shifts, omit if not used -->
|-

! {{Chemical datatable header}} | [[Mass Spectrometry|MS]]
|-
| Masses of <br/>main fragments
| ESI-MS [M+H]<sup>+</sup> ''m''/''z'' : 291.0
<br/>273 water loss
<br/>139 retro Diels–Alder
<br/>123
<br/>165
<br/>147
|-
|}