{{Chembox | Watchedfields = changed | verifiedrevid = 443671399 | Name = Caffeic acid | ImageFile1 = Kaffeesäure.svg | ImageClass1 = skin-invert-image | ImageName1 = 2D diagram of caffeic acid | ImageFile2 = Cafeic-acid-3D.png | ImageClass2 = bg-transparent | ImageName2 = 3D ball-and-stick model of caffeic acid | ImageFile3 = CaffeicAcid3d.png | ImageClass3 = bg-transparent | ImageName3 = 3D space filling model of caffeic acid | PIN = (2''E'')-3-(3,4-Dihydroxyphenyl)prop-2-enoic acid | IUPACName = 3-(3,4-Dihydroxyphenyl)-2-propenoic acid<br />3,4-Dihydroxycinnamic acid<br />''trans''-Caffeate<br />3,4-Dihydroxy-''trans''-cinnamate<br/>(''E'')-3-(3,4-dihydroxyphenyl)-2-propenoic acid<br />3,4-Dihydroxybenzeneacrylicacid<br />3-(3,4-Dihydroxyphenyl)-2-propenoic acid |Section1={{Chembox Identifiers | IUPHAR_ligand = 5155 | Beilstein = 1954563 | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 16433 | DrugBank_Ref = {{drugbankcite|correct|drugbank}} | DrugBank = DB01880 | SMILES = O=C(O)\C=C\c1cc(O)c(O)cc1 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 600426 | PubChem = 689043 | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 145 | EC_number = 206-361-2 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = U2S3A33KVM | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = C01481 | InChI = 1/C9H8O4/c10-7-3-1-6(5-8(7)11)2-4-9(12)13/h1-5,10-11H,(H,12,13)/b4-2+ | InChIKey = QAIPRVGONGVQAS-DUXPYHPUBE | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C9H8O4/c10-7-3-1-6(5-8(7)11)2-4-9(12)13/h1-5,10-11H,(H,12,13)/b4-2+ | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = QAIPRVGONGVQAS-DUXPYHPUSA-N | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 501-16-6 | CASNo1_Ref = {{cascite|correct|CAS}} | CASNo1 = 331-39-5 | CASNo1_Comment = (non-specific)

}} |Section2 = {{Chembox Properties | Formula = C<sub>9</sub>H<sub>8</sub>O<sub>4</sub> | MolarMass = 180.16 g/mol | Density = 1.478 g/cm<sup>3</sup> | MeltingPtC = 223 to 225 | BoilingPt = | LambdaMax = 327&nbsp;nm and a shoulder at c. 295&nbsp;nm in acidified methanol<ref>{{cite journal | title = Functional role of anthocyanins in the leaves of ''Quintinia serrata'' A. Cunn. |first1=Kevin S. |last1=Gould |first2=Kenneth R. |last2=Markham |first3=Richard H. |last3=Smith |first4=Jessica J. |last4=Goris | journal = Journal of Experimental Botany | volume = 51 | issue = 347 | pages = 1107–1115 | year = 2000 | doi = 10.1093/jexbot/51.347.1107 | pmid = 10948238| doi-access = free }}</ref> }} |Section5={{Chembox Hazards | NFPA-H = 1 | NFPA-F = 1 | NFPA-R = 0 | GHSPictograms = {{GHS07}}{{GHS08}} | GHSSignalWord = Warning | HPhrases = {{H-phrases|315|319|335|351|361}} | PPhrases = {{P-phrases|201|202|261|264|271|280|281|302+352|304+340|305+351+338|308+313|312|321|332+313|337+313|362|403+233|405|501}} }} |Section8 = {{Chembox Related | OtherCompounds = Chlorogenic acid<br/>Cichoric acid<br/>Coumaric acid<br/>Quinic acid }} }}

'''Caffeic acid''' is an organic compound with the formula {{chem2|(HO)2C6H3CH\dCHCO2H}}. It plays a key role in scavenging reactive oxygen species (ROS) generated in energy metabolism. Caffeic acid is also responsible for maintaining normal levels of nitric oxide (NO) within cells. Caffeic acid is a yellow, solid chemical compound that is structurally classified as a hydroxycinnamic acid, and the molecule consists of both phenolic and acrylic functional groups. Caffeic acid is found in all plants as an intermediate in the biosynthesis of lignin, a naturally occurring complex carbohydrate representing the principal components of biomass and its residues.<ref name=Boerjan/> It is chemically unrelated to caffeine; instead, the shared name is related to its presence in coffee.

== Natural occurrences == Caffeic acid can be found in the bark of ''Eucalyptus globulus''<ref>{{Cite journal|pmid=21761864|doi=10.1021/jf201801q|title=Characterization of Phenolic Components in Polar Extracts of Eucalyptus globulus Labill. Bark by High-Performance Liquid Chromatography–Mass Spectrometry|year=2011|last1=Santos|first1=Sónia A. O.|last2=Freire|first2=Carmen S. R.|last3=Domingues|first3=M. Rosário M.|last4=Silvestre|first4=Armando J. D.|last5=Pascoal Neto|first5=Carlos|journal=Journal of Agricultural and Food Chemistry|volume=59|issue=17|pages=9386–9393 |bibcode=2011JAFC...59.9386S }}</ref>, the barley grain ''Hordeum vulgare'', and the herb ''Dipsacus asperoides''.<ref>{{Cite journal|title=The Liquid Chromatographic Determination of Chlorogenic and Caffeic Acids in Xu Duan (Dipsacus asperoides) Raw Herb|last1=Khoo|first1=Cheang S.|last2=Sullivan|first2=Shaun|date=2014|journal=ISRN Analytical Chemistry|language=en|last3=Kazzem|first3=Magdy|last4=Lamin|first4=Franklin|last5=Singh|first5=Swastika|last6=Nang|first6=Marnilar|last7=Low|first7=Mitchell|last8=Suresh|first8=Harsha|last9=Lee|first9=Samiuela|volume=2014|pages=1–6|doi=10.1155/2014/968314|doi-access=free}}</ref> It can also be found in the freshwater fern ''Salvinia molesta''<ref>{{cite journal|pmid=18177906|doi=10.1016/j.phytochem.2007.10.028|title=Phenolic and other constituents of fresh water fern ''Salvinia molesta''|year=2008|last1=Choudhary|first1=M. Iqbal|last2=Naheed|first2=Nadra|last3=Abbaskhan|first3=Ahmed|last4=Musharraf|first4=Syed Ghulam|last5=Siddiqui|first5=Hina|last6=Atta-Ur-Rahman|journal=Phytochemistry|volume=69|issue=4|pages=1018–1023|bibcode=2008PChem..69.1018C }}</ref> and in the mushroom ''Phellinus linteus''.<ref name="pmid18827365">{{cite journal|doi=10.1248/bpb.31.1968 |last1=Lee |first1=Y.-S. |title=Protein glycation inhibitors from the fruiting body of ''Phellinus linteus'' |journal=Biological & Pharmaceutical Bulletin |volume=31 |issue=10 |pages=1968–1972 |date=October 2008 |pmid=18827365 |last2=Kang |first2=Y.-H. |last3=Jung |first3=J.-Y. |last4=Lee |first4=Sanghyun |last5=Ohuchi |first5=Kazuo |last6=Shin |first6=Kuk Hyun |last7=Kang |first7=Il-Jun |last8=Park |first8=Jung Han Yoon |last9=Shin |first9=Hyun-Kyung |last10=Soon |first10=Sung |doi-access=free }}</ref>

=== Occurrences in food === Free caffeic acid can be found in a variety of beverages, including brewed coffee at 63.1-96.0&nbsp;mg per 100&nbsp;ml<ref>{{cite journal|title=Determination of free and total phenolic acids in plant-derived foods by HPLC with diode-array detection|first1=Mittila|last1=Pirjo|first2=Jorma|last2=Kumpulainen|date=19 June 2002|journal=J Agric Food Chem|volume=50|issue=13 |pages=3660–7|doi=10.1021/jf020028p|pmid= 12059140 |bibcode=2002JAFC...50.3660M }}</ref> and red wine at 2&nbsp;mg per 100&nbsp;ml.<ref>{{cite web | url=http://phenol-explorer.eu/contents/polyphenol/457 | title=Showing all foods in which the polyphenol Caffeic acid is found - Phenol-Explorer }}</ref> It is found at relatively high levels in herbs of the mint family, especially thyme, sage and spearmint (at about 20&nbsp;mg per 100&nbsp;g), and in spices, such as Ceylon cinnamon and star anise (at about 22&nbsp;mg per 100&nbsp;g). Caffeic acid occurs at moderate levels in sunflower seeds (8&nbsp;mg per 100&nbsp;g), apple sauce, apricots and prunes (at about 1&nbsp;mg per 100&nbsp;g).<ref>{{cite journal | url=https://www.ncbi.nlm.nih.gov/books/NBK513593/ | pmid=8411618 | year=1993 | title=Caffeic acid | journal=Iarc Monographs on the Evaluation of Carcinogenic Risks to Humans | volume=56 | pages=115–134 | pmc=7681336 }}</ref> It occurs at remarkably high levels in black chokeberry (141&nbsp;mg per 100&nbsp;g).<ref>{{cite journal|title=Oxygen radical absorbing capacity of phenolics in blueberries, cranberries, chokeberries, and lingonberries|first1=Wei|last1=Zheng|first2=Shiow Y|last2=Wang|date=15 January 2003|journal=J Agric Food Chem|volume=51|issue=2 |pages=502–9|doi=10.1021/jf020728u|pmid= 12517117 |bibcode=2003JAFC...51..502Z }}</ref> It is also quite high in the South American herb yerba mate (150&nbsp;mg per 100&nbsp;g based on thin-layer chromatography densitometry<ref>{{cite journal|title=Determination of Flavonoids, Phenolic Acids, and Xanthines in Mate Tea (''Ilex paraguariensis'' St.-Hil.)|first1=Mirza|last1=Bojić|first2=Vicente Simon|last2=Haas|first3=Darija|last3=Šarić|first4=Željan|last4=Maleš|date=4 April 2018|journal=Journal of Analytical Methods in Chemistry|volume=2013|article-number=658596|doi=10.1155/2013/658596|pmid=23841023|pmc=3690244|doi-access=free}}</ref> and HPLC<ref>{{cite journal|doi=10.1021/jf2008343 | pmid=21510640 | volume=59 | issue=10 | title=Chemical Composition and Antioxidant Activity of Yerba-Mate (''Ilex paraguariensis'' A. St.-Hil., Aquifoliaceae) Extract as Obtained by Spray Drying | journal=Journal of Agricultural and Food Chemistry | pages=5523–5527 | last1 = Berté | first1 = Kleber A. S.| year=2011 | bibcode=2011JAFC...59.5523B }}</ref>). It is also found at lower levels in barley and rye.<ref>{{cite journal | last1 = Quinde-Axtell | first1 = Zory | last2 = Baik | first2 = Byung-Kee | year = 2006 | title = Phenolic Compounds of Barley Grain and Their Implication in Food Product Discoloration | journal = J. Agric. Food Chem. | volume = 54 | issue = 26 | pages = 9978–9984 | doi = 10.1021/jf060974w | pmid=17177530 | bibcode = 2006JAFC...54.9978Q }}</ref>

=== Biosynthesis === Caffeic acid is biosynthesized by hydroxylation of coumaroyl ester of quinic acid (esterified through a side chain alcohol). This hydroxylation produces the caffeic acid ester of shikimic acid, which converts to chlorogenic acid. It is the precursor to ferulic acid, coniferyl alcohol, and sinapyl alcohol, all of which are significant building blocks in lignin.<ref name=Boerjan>{{cite journal|doi=10.1146/annurev.arplant.54.031902.134938|title=Lignin biosynthesis|year=2003|last1=Boerjan|first1=Wout|last2=Ralph|first2=John|last3=Baucher|first3=Marie|journal=Annual Review of Plant Biology|volume=54|issue=1 |pages=519–546|pmid=14503002|bibcode=2003AnRPB..54..519B |url=https://biblio.ugent.be/publication/211742/file/4144786|url-access=subscription}}</ref> The transformation to ferulic acid is catalyzed by the enzyme caffeate ''O''-methyltransferase.

Caffeic acid and its derivative caffeic acid phenethyl ester (CAPE) are produced in many kinds of plants.<ref>{{cite web|url=http://indigo-herbs.co.uk/acatalog/Red_Clover_Flowers_Info.html|title=Red Clover Benefits & Information|website=indigo-herbs.co.uk|access-date=4 April 2018|archive-date=7 November 2012|archive-url=https://web.archive.org/web/20121107084645/http://www.indigo-herbs.co.uk/acatalog/Red_Clover_Flowers_Info.html|url-status=dead}}</ref><ref name="urlActivities of a Specific Chemical Query">{{cite web |url=http://www.ars-grin.gov/cgi-bin/duke/chemical.pl?CAFFEICACID |title=Dr. Duke's Phytochemical and Ethnobotanical Databases |archive-url=https://web.archive.org/web/20001205192000/http://www.ars-grin.gov/cgi-bin/duke/chemical.pl?CAFFEICACID |archive-date=2000-12-05 }}</ref><ref name="pmid11208940"/>

:[[Image:CaffeicAcIn.png|thumb|class=skin-invert-image|300px|left|In plants, caffeic acid (middle) is formed from 4-hydroxycinnamic acid (left) and is transformed to ferulic acid.]] {{clear left}}

Dihydroxyphenylalanine ammonia-lyase was presumed to use 3,4-dihydroxy-<small>L</small>-phenylalanine (<small>L</small>-DOPA) to produce trans-caffeate and NH<sub>3</sub>. However, the EC number for this purported enzyme was deleted in 2007, as no evidence has emerged for its existence.<ref>{{cite web|url=http://www.chem.qmul.ac.uk/iubmb/enzyme/EC4/3/1/11.html|title=EC 4.3.1.11|website=www.chem.qmul.ac.uk|access-date=4 April 2018|archive-url=https://web.archive.org/web/20160303180117/http://www.chem.qmul.ac.uk/iubmb/enzyme/EC4/3/1/11.html|archive-date=3 March 2016}}</ref>

=== Biotransformation === Caffeate ''O''-methyltransferase is an enzyme responsible for the transformation of caffeic acid into ferulic acid.

Caffeic acid and related ''o''-diphenols are rapidly oxidized by ''o''-diphenol oxidases in tissue extracts.<ref>{{cite journal | last1 = Pierpoint | first1 = W. S. | year = 1969 | title = ''o''-Quinones formed in plant extracts. Their reactions with amino acids and peptides | journal = Biochem. J. | volume = 112 | issue = 5| pages = 609–616 | doi=10.1042/bj1120609| pmid = 4980678 | pmc = 1187763 }}</ref>

=== Biodegradation === Caffeate 3,4-dioxygenase is an enzyme that uses caffeic acid and oxygen to produce 3-(2-carboxyethenyl)-''cis'',''cis''-muconate.

Caffeic acid is susceptible to autoxidation. Glutathione and thiol compounds (cysteine, thioglycolic acid or thiocresol) or ascorbic acid have a protective effect on browning and disappearance of caffeic acid.<ref>{{cite journal | last1 = Cilliers | first1 = Johannes J. L. | last2 = Singleton | first2 = Vernon L. | year = 1990 | title = Caffeic acid autoxidation and the effects of thiols | journal = J. Agric. Food Chem. | volume = 38 | issue = 9| pages = 1789–1796 | doi = 10.1021/jf00099a002 | bibcode = 1990JAFC...38.1789C }}</ref> This browning is due to the conversion of ''o''-diphenols into reactive ''o''-quinones. Chemical oxidation of caffeic acid in acidic conditions using sodium periodate leads to the formation of dimers with a furan structure (isomers of 2,5-(3′,4′-dihydroxyphenyl)tetrahydrofuran 3,4-dicarboxylic acid).<ref>{{cite journal | last1 = Fulcrand | first1 = Hélène | last2 = Cheminat | first2 = Annie | last3 = Brouillard | first3 = Raymond | last4 = Cheynier | first4 = Véronique | year = 1994 | title = Characterization of compounds obtained by chemical oxidation of caffeic acid in acidic conditions | journal = Phytochemistry | volume = 35 | issue = 2| pages = 499–505 | doi = 10.1016/S0031-9422(00)94790-3 | bibcode = 1994PChem..35..499F }}</ref> Caffeic acid can also be polymerized using the horseradish peroxidase/H<sub>2</sub>O<sub>2</sub> oxidizing system.<ref>{{cite journal | last1 = Xu | first1 = Peng | last2 = Uyama | first2 = Hiroshi | last3 = Whitten | first3 = James E. | last4 = Kobayashi | first4 = Shiro |author5-link=David L. Kaplan (engineer) | last5 = Kaplan | first5 = David L. | year = 2005 | title = Peroxidase-Catalyzed in Situ Polymerization of Surface Orientated Caffeic Acid | journal = J. Am. Chem. Soc. | volume = 127 | issue = 33| pages = 11745–11753 | doi = 10.1021/ja051637r | pmid=16104752 | bibcode = 2005JAChS.12711745X }}</ref>

== Glycosides == 3-''O''-caffeoylshikimic acid (dactylifric acid) and its isomers, are enzymic browning substrates found in dates (''Phoenix dactylifera'' fruits).<ref>{{Cite journal|pmid=5836492|year=1964|last1=Maier|first1=V. P.|last2=Metzler|first2=D. M.|last3=Huber|first3=A. F.|title=3-''O''-Caffeoylshikimic acid (dactylifric acid) and its isomers, a new class of enzymic browning substrates|volume=14|issue=2|pages=124–128|journal=Biochemical and Biophysical Research Communications|doi=10.1016/0006-291x(64)90241-4 |bibcode=1964BBRC...14..124M }}</ref>

== Pharmacology == Caffeic acid has a variety of potential pharmacological effects in ''in vitro'' studies and in animal models, and the inhibitory effect of caffeic acid on cancer cell proliferation by an oxidative mechanism in the human HT-1080 fibrosarcoma cell line has been established.<ref>{{cite journal | last1 = Rajendra Prasad | first1 = N. | last2 = Karthikeyan | first2 = A. | last3 = Karthikeyan | first3 = S. | last4 = Reddy | first4 = B. V. | date = Mar 2011 | title = Inhibitory effect of caffeic acid on cancer cell proliferation by oxidative mechanism in human HT-1080 fibrosarcoma cell line | journal = Mol Cell Biochem | volume = 349 | issue = 1–2| pages = 11–19 | doi = 10.1007/s11010-010-0655-7 | pmid = 21116690 | s2cid = 28014579 }}</ref>

Caffeic acid is an antioxidant ''in vitro'' and also ''in vivo''.<ref name="pmid11208940">{{cite journal |last1=Olthof |first1=M. R. |last2=Hollman |first2=P. C. |last3=Katan |first3=M. B. |title=Chlorogenic acid and caffeic acid are absorbed in humans |journal=J. Nutr. |volume=131 |issue=1 |pages=66–71 |date=January 2001 |pmid=11208940 |doi= 10.1093/jn/131.1.66|doi-access=free }}</ref> Caffeic acid also shows immunomodulatory and anti-inflammatory activity. Caffeic acid outperformed the other antioxidants, reducing aflatoxin production by more than 95 percent. The studies are the first to show that oxidative stress that would otherwise trigger or enhance ''Aspergillus flavus'' aflatoxin production can be stymied by caffeic acid. This opens the door to use as a natural fungicide by supplementing trees with antioxidants.<ref name="urlNuts'New Aflatoxin Fighter: Caffeic Acid?">{{cite web |url=https://agresearchmag.ars.usda.gov/2006/oct/nuts |title=Nuts' New Aflatoxin Fighter: Caffeic Acid? }}</ref>

Studies of the carcinogenicity of caffeic acid have mixed results. Some studies have shown that it inhibits carcinogenesis, and other experiments show carcinogenic effects.<ref name= Hirose>{{cite journal|journal=Carcinogenesis|volume=19|pages=207–212|year=1998|title=Carcinogenicity of antioxidants BHA, caffeic acid, sesamol, 4-methoxyphenol and catechol at low doses, either alone or in combination, and modulation of their effects in a rat medium-term multi-organ carcinogenesis model|first1=M. |last1=Hirose |first2=Y. |last2=Takesada |first3=H. |last3=Tanaka |first4=S. |last4=Tamano |first5=T. |last5=Kato |first6=T. |last6=Shirai |doi=10.1093/carcin/19.1.207|pmid=9472713|issue=1|doi-access=free }}</ref> Oral administration of high doses of caffeic acid in rats has caused stomach papillomas.<ref name= Hirose/> In the same study, high doses of combined antioxidants, including caffeic acid, showed a significant decrease in growth of colon tumors in those same rats. No significant effect was noted otherwise. Caffeic acid is listed under some Hazard Data sheets as a potential carcinogen,<ref name="urlCaffeic Acid (IARC Summary & Evaluation, Volume 56, 1993)">{{cite web |url=http://www.inchem.org/documents/iarc/vol56/03-caff.html |title=Caffeic Acid |work=IARC Summary & Evaluation |volume= 56 |date=1993 }}</ref> as has been listed by the International Agency for Research on Cancer as a Group 2B carcinogen ("possibly carcinogenic to humans").<ref>{{cite web|url=http://monographs.iarc.fr/ENG/Classification/ClassificationsGroupOrder.pdf|title=Agents Classified by the IARC Monographs|publisher=International Agency for Research on Cancer|website=iarc.fr|access-date=4 April 2018|archive-url=https://web.archive.org/web/20111025122327/http://monographs.iarc.fr/ENG/Classification/ClassificationsGroupOrder.pdf|archive-date=25 October 2011}}</ref> More recent data show that bacteria in the rats' guts may alter the formation of metabolites of caffeic acid.<ref>{{cite journal|journal=Proceedings of the National Academy of Sciences|volume=69|pages=1413–1415|year=1972|title=Caffeic acid metabolism by gnotobiotic rats and their intestinal bacteria|first1=M. A. |last1=Peppercorn |first2=P. |last2=Goldman |pmid=4504351|doi=10.1073/pnas.69.6.1413|issue=6|pmc=426714|bibcode=1972PNAS...69.1413P|doi-access=free}}</ref><ref>{{cite journal|journal=Journal of Nutrition|volume=133|pages=1853–1859|date=1 June 2003|title=Chlorogenic acid bioavailability largely depends on its metabolism by the gut microflora in rats|first1=M.-P. |last1=Gonthier |first2=M.-A. |last2=Verny |first3=C. |last3=Besson |first4=C. |last4=Rémésy |first5=A. |last5=Scalbert |pmid=12771329|issue=6|doi=10.1093/jn/133.6.1853|doi-access=free }}</ref> Other than caffeic acid being a thiamine antagonist (antithiamine factor), there have been no known ill effects of caffeic acid in humans. Also, caffeic acid treatment attenuated lipopolysaccharide (LPS)-induced sickness behaviour in experimental animals by decreasing both peripheral and central cytokine levels along with oxidative stress inflicted by LPS.<ref>{{cite journal|last1=Basu|first1=Mallik S|display-authors=et al|title=Caffeic acid attenuates lipopolysaccharide-induced sickness behaviour and neuroinflammation in mice.|journal=Neuroscience Letters|volume=632|pages=218–223|date=3 Sep 2016|doi=10.1016/j.neulet.2016.08.044|pmid=27597761|s2cid=5361129}}</ref>

== Other uses == Caffeic acid may be the active ingredient in caffenol, a do-it-yourself black-and-white photographic developer made from instant coffee.<ref>{{cite web|website=Caffenol blog|url=https://caffenol.blogspot.com/2010/03/caffenol-c-m-recipe.html|title=Caffenol-C-M, recipe|date=2 March 2010}}</ref> The developing chemistry is similar to that of catechol or pyrogallol.<ref>{{cite web|last=Williams|first=Scott|url=http://people.rit.edu/andpph/text-coffee.html|title=A Use for that Last Cup of Coffee: Film and Paper Development |work=Technical Photographic Chemistry 1995 Class|publisher=Imaging and Photographic Technology Department, School of Photographic Arts and Sciences, Rochester Institute of Technology}}</ref>

It is also used as a matrix in MALDI mass spectrometry analyses.<ref name="pmid2520223">{{cite journal |last1= Beavis |first1=R. C. |last2=Chait |first2=B. T. |title=Cinnamic acid derivatives as matrices for ultraviolet laser desorption mass spectrometry of proteins |journal=Rapid Commun. Mass Spectrom. |volume=3 |issue=12 |pages=432–435 |date=Dec 1989 |pmid=2520223 |doi=10.1002/rcm.1290031207 |bibcode=1989RCMS....3..432B }}</ref>

== Isomers == Isomers with the same molecular formula and in the hydroxycinammic acids family are: * Umbellic acid (2,4-dihydroxycinnamic acid) * 2,3-Dihydroxycinnamic acid * 2,5-Dihydroxycinnamic acid

== References == {{Reflist|30em}}

{{Coffee}} {{Hydroxycinnamic acid}} {{Leukotrienergics}} {{Purinergics}}

{{DEFAULTSORT:Caffeic Acid}} Category:IARC Group 2B carcinogens Category:Hydroxycinnamic acids Category:Xanthine oxidase inhibitors Category:Catechols Category:Phenylogous carboxylic acids