Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Purine: Difference between pages

{{Short description|Heterocyclic aromatic organic compound}}

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| ImageFile1 = Purine-3D-balls.png

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| ImageFile2 = Purine-3D-spacefill.png

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| ImageAlt2 = Space-filling molecular model

| IUPACName=9''H''-purine

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| UNII = W60KTZ3IZY

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| MeSHName=Purine

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'''Purine''' is a [[heterocyclic compound|heterocyclic]] [[aromatic]] [[organic compound]] that consists of two rings ([[pyrimidine]] and [[imidazole]]) fused together. It is [[water]]-soluble. Purine also gives its name to the wider class of [[molecule]]s, '''purines''', which include substituted purines and their [[tautomer]]s. They are the most widely occurring [[nitrogen]]-containing heterocycles in nature.<ref>{{cite journal | vauthors = Rosemeyer H | title = The chemodiversity of purine as a constituent of natural products | journal = Chemistry & Biodiversity | volume = 1 | issue = 3 | pages = 361–401 | date = March 2004 | pmid = 17191854 | doi = 10.1002/cbdv.200490033 | s2cid = 12416667 }}</ref>

== Dietary sources ==

Purines are found in high concentration in meat and meat products, especially internal organs such as [[liver]] and [[kidney]]. In general, plant-based diets are low in purines.<ref>{{cite web |url=http://www.dietaryfiberfood.com/purine-food.php |title=Gout: List of Foods High and Low in Purine Content |website=Dietaryfiberfood.com |date=2016-04-08 |access-date=2016-07-16 |archive-date=2011-11-12 |archive-url=https://web.archive.org/web/20111112133438/http://www.dietaryfiberfood.com/purine-food.php |url-status=live }}</ref> High-purine plants and algae include some legumes ([[lentil]]s, [[soybeans]], and [[black-eyed pea]]s) and [[Spirulina (dietary supplement)|spirulina]]. Examples of high-purine sources include: [[sweetbread]]s, [[Anchovies as food|anchovies]], [[Sardines as food|sardines]], liver, [[beef]] kidneys, [[Brain as food|brain]]s, [[meat extract]]s (e.g., [[Oxo (food)|Oxo]], [[Bovril]]), [[herring]], [[mackerel]], [[scallop]]s, [[game meat]]s, [[yeast]] ([[beer]], [[yeast extract]], [[nutritional yeast]]) and [[gravy]].<ref>{{cite journal | vauthors = Kaneko K, Aoyagi Y, Fukuuchi T, Inazawa K, Yamaoka N | title = Total purine and purine base content of common foodstuffs for facilitating nutritional therapy for gout and hyperuricemia | journal = Biological & Pharmaceutical Bulletin | volume = 37 | issue = 5 | pages = 709–721 | date = 2014 | pmid = 24553148 | doi = 10.1248/bpb.b13-00967 | doi-access = free }}</ref>

A moderate amount of purine is also contained in red meat, [[beef]], [[pork]], [[poultry]], fish and [[seafood]], [[asparagus]], [[cauliflower]], [[spinach]], [[Edible mushroom|mushrooms]], [[green pea]]s, [[lentil]]s, dried peas, [[bean]]s, [[oatmeal]], [[wheat bran]], [[wheat germ]], and [[Crataegus monogyna#Edible "berries", petals, and leaves|haws]].<ref>{{cite web |url=http://www.healthcastle.com/gout.shtml |title=Gout Diet: What Foods To Avoid |website=Healthcastle.com |access-date=2016-07-16 |archive-date=2017-08-14 |archive-url=https://web.archive.org/web/20170814152322/http://www.healthcastle.com/gout.shtml |url-status=live }}</ref>

== Biochemistry ==

Purines and [[pyrimidine]]s make up the two groups of [[nitrogenous base]]s, including the two groups of [[nucleotide bases]]. The purine bases are [[guanine]] (G) and [[adenine]] (A) which form corresponding nucleosides-[[deoxyribonucleoside]]s ([[deoxyguanosine]] and [[deoxyadenosine]]) with deoxyribose moiety and [[ribonucleoside]]s ([[guanosine]], [[adenosine]]) with ribose moiety. These nucleosides with phosphoric acid form corresponding nucleotides (deoxyguanylate, deoxyadenylate and guanylate, adenylate) which are the building blocks of [[DNA]] and [[RNA]], respectively. Purine bases also play an essential role in many metabolic and signalling processes within the compounds [[guanosine monophosphate]] (GMP) and [[adenosine monophosphate]] (AMP).

In order to perform these essential cellular processes, both purines and pyrimidines are needed by the [[Cell (biology)|cell]], and in similar quantities. Both purine and pyrimidine are self-[[Enzyme inhibitor|inhibiting]] and [[Enzyme activator|activating]]. When purines are formed, they [[Enzyme inhibition|inhibit]] the [[enzyme]]s required for more purine formation. This self-inhibition occurs as they also activate the enzymes needed for pyrimidine formation. Pyrimidine simultaneously self-inhibits and activates purine in a similar manner. Because of this, there is nearly an equal amount of both substances in the cell at all times.<ref>{{Cite book|title=Textbook of Medical Physiology|url=https://archive.org/details/textbookmedicalp00acgu|url-access=limited| vauthors = Guyton AC |publisher=Elsevier|year=2006|isbn=978-0-7216-0240-0 |page=[https://archive.org/details/textbookmedicalp00acgu/page/n71 37]}}</ref>

==Properties==

Purine is both a very weak acid ([[Acid dissociation constant|pK_a]] 8.93) and an even weaker base ([[Acid dissociation constant|pK_a]] 2.39).<ref>{{cite book| vauthors = Seela F |display-authors=etal| veditors = Schaumann E |title=Houben-Weyl Methods of Organic Chemistry | volume = E 9b/2 | edition = 4th Supplement |chapter=Hetarenes III (Six-Membered Rings and Larger Hetero-Rings with Maximum Unsaturation) — Part 2b|date=2014|isbn=978-3-13-181504-0|page=310|publisher=Thieme |url=https://books.google.com/books?id=wy2GAwAAQBAJ&pg=PA310|access-date=2020-05-15|archive-date=2022-02-17|archive-url=https://web.archive.org/web/20220217094219/https://books.google.com/books?id=wy2GAwAAQBAJ&pg=PA310|url-status=live}}</ref> If dissolved in pure water, the [[pH]] is halfway between these two pKa values.

Purine is [[Aromaticity|aromatic]], having four [[tautomer]]s each with a hydrogen bonded to a different one of the four nitrogen atoms. These are identified as 1-H, 3-H, 7-H, and 9-H (see image of numbered ring). The common crystalline form favours the 7-H tautomer, while in polar solvents both the 9-H and 7-H tautomers predominate.<ref>{{cite journal | vauthors = Raczyńska ED, Gal JF, Maria PC, Kamińska B, Igielska M, Kurpiewski J, Juras W | title = Purine tautomeric preferences and bond-length alternation in relation with protonation-deprotonation and alkali metal cationization | journal = Journal of Molecular Modeling | volume = 26 | issue = 5 | pages = 93 | date = April 2020 | pmid = 32248379 | pmc = 7256107 | doi = 10.1007/s00894-020-4343-6 }}</ref> Substituents to the rings and interactions with other molecules can shift the equilibrium of these tautomers.<ref>{{cite journal | vauthors = Stasyuk OA, Szatyłowicz H, Krygowski TM | title = Effect of the H-bonding on aromaticity of purine tautomers | journal = The Journal of Organic Chemistry | volume = 77 | issue = 8 | pages = 4035–45 | date = April 2012 | pmid = 22448684 | doi = 10.1021/jo300406r }}</ref>

==Notable purines==

There are many naturally occurring purines. They include the [[nucleobase]]s [[adenine]] ('''2''') and [[guanine]] ('''3'''). In [[DNA]], these bases form [[hydrogen bond]]s with their [[complementarity (molecular biology)|complementary]] [[pyrimidine]]s, [[thymine]] and [[cytosine]], respectively. This is called complementary base pairing. In [[RNA]], the complement of adenine is [[uracil]] instead of thymine.

Other notable purines are [[hypoxanthine]], [[xanthine]], [[theophylline]], [[theobromine]], [[caffeine]], [[uric acid]] and [[isoguanine]].

[[Image:purines.svg|550px]]{{Contradict-inline|Xanthine|reason=Xanthine has hydrogen on atom 7, not 9.}}

==Functions==

[[File:Blausen 0323 DNA Purines.png|thumb|The main purine-derived [[nucleobase]]s.]]

Aside from the crucial roles of purines (adenine and guanine) in DNA and RNA, purines are also significant components in a number of other important biomolecules, such as [[Adenosine triphosphate|ATP]], [[Guanosine triphosphate|GTP]], [[cyclic AMP]], [[NADH]], and [[coenzyme A]]. Purine ('''1''') itself, has not been found in nature, but it can be produced by [[organic synthesis]].

They may also function directly as [[neurotransmitters]], acting upon [[purinergic receptors]]. Adenosine activates [[adenosine receptor]]s.

== History ==

The word ''purine'' (''pure urine'')<ref name="McGuigan">{{cite book | vauthors = McGuigan H |title=An Introduction To Chemical Pharmacology |url=http://www.ebooksread.com/authors-eng/hugh-mcguigan/an-introduction-to-chemical-pharmacology-pharmacodynamics-in-relation-to--goo/page-20-an-introduction-to-chemical-pharmacology-pharmacodynamics-in-relation-to--goo.shtml |publisher=P. Blakiston's Sons & Co. |year=1921 |page=283 |access-date=July 18, 2012 |archive-date=April 16, 2020 |archive-url=https://web.archive.org/web/20200416132051/http://www.ebooksread.com/authors-eng/hugh-mcguigan/an-introduction-to-chemical-pharmacology-pharmacodynamics-in-relation-to--goo/page-20-an-introduction-to-chemical-pharmacology-pharmacodynamics-in-relation-to--goo.shtml |url-status=live }}</ref> was coined by the [[Germany|German]] [[chemist]] [[Emil Fischer]] in 1884.<ref>{{cite journal | vauthors = Fischer E |date=1884 |url=https://zenodo.org/record/1425341/files/article.pdf |title=Ueber die Harnsäure. I. |trans-title=On uric acid. I. |journal=Berichte der Deutschen Chemischen Gesellschaft |volume=17 |pages=328–338 |doi=10.1002/cber.18840170196 |access-date=2016-04-20 |archive-date= |archive-url= |url-status= }} {{open access}}<br>[https://babel.hathitrust.org/cgi/pt?id=uiug.30112025692879;view=1up;seq=343 From p. 329] {{Webarchive|url=https://web.archive.org/web/20220217094238/https://babel.hathitrust.org/cgi/pt?id=uiug.30112025692879;view=1up;seq=343;a=zoom:1 |date=2022-02-17 }}: ''"Um eine rationelle Nomenklatur der so entstehenden zahlreichen Substanzen zu ermöglichen, betrachte ich dieselben als Abkömmlinge der noch unbekannten Wasserstoffverbindung CH₃.C₅N₄H₃ and nenne die letztere Methylpurin."'' (In order to make possible a rational nomenclature for the numerous existing substances, I regarded them as derivatives of a still unknown hydrogen compound, CH₃.C₅N₄H₃, and call the latter "methylpurine".)</ref><ref name=Fischer1898>{{cite journal | vauthors = Fischer E |date=1898 |url=https://zenodo.org/record/1425916/files/article.pdf |title=Ueber das Purin und seine Methylderivate |trans-title=On purine and its methyl derivatives |journal=Berichte der Deutschen Chemischen Gesellschaft |volume=31 |issue=3 |pages=2550–74 |doi=10.1002/cber.18980310304 |access-date=2016-04-20 |archive-date= |archive-url= |url-status= }} {{open access}}<br>[https://babel.hathitrust.org/cgi/pt?id=hvd.cl1i1u;view=1up;seq=14 From p. 2550] {{Webarchive|url=https://web.archive.org/web/20201018131621/https://babel.hathitrust.org/cgi/pt?id=hvd.cl1i1u;view=1up;seq=14 |date=2020-10-18 }}: ''"…hielt ich es für zweckmäßig, alle diese Produkte ebenso wie die Harnsäure als Derivate der sauerstofffreien Verbindung C₅H₄N₄ zu betrachten, und wählte für diese den Namen Purin, welcher aus den Wörtern purum und uricum kombiniert war."'' (…I regarded it as expedient to consider all of these products, just like uric acid, as derivatives of the oxygen-free compound C₅H₄N₄, and chose for them the name "purine", which was formed from the [Latin] words ''purum'' and ''uricum''.)</ref> He synthesized it for the first time in 1898.<ref name=Fischer1898/> The starting material for the reaction sequence was [[uric acid]] ('''8'''), which had been isolated from [[kidney stone]]s by [[Carl Wilhelm Scheele]] in 1776.<ref>{{cite journal | vauthors = Scheele CW | year = 1776 | title = Examen chemicum calculi urinari | trans-title = A chemical examination of kidney stones | journal = Opuscula | volume = 2 | page = 73 }}</ref> Uric acid (8) was reacted with [[phosphorus pentachloride|PCl₅]] to give 2,6,8-trichloropurine ('''10'''), which was converted with [[hydrogen iodide|HI]] and [[Phosphonium iodide|PH₄I]] to give 2,6-diiodopurine ('''11'''). The product was reduced to purine ('''1''') using [[zinc]] dust.

[[Image:FischerPurineSynthesis.gif]]

== Metabolism ==<!-- This section is linked from [[Metabolism]] -->

{{main article|Purine metabolism}}

Many organisms have [[metabolic pathway]]s to synthesize and break down purines.

Purines are biologically synthesized as [[nucleoside]]s (bases attached to [[ribose]]).

Accumulation of modified purine nucleotides is defective to various cellular processes, especially those involving [[DNA]] and [[RNA]]. To be viable, organisms possess a number of deoxypurine phosphohydrolases, which [[hydrolyze]] these purine derivatives removing them from the active [[Nucleoside triphosphate|NTP]] and [[Deoxynucleoside triphosphate|dNTP]] pools. Deamination of purine bases can result in accumulation of such nucleotides as [[Inosine triphosphate|ITP]], [[Deoxyinosine triphosphate|dITP]], [[Xanthosine triphosphate|XTP]] and [[Deoxyxanthosine triphosphate|dXTP]].<ref name="pmid 22531138">{{cite journal | vauthors = Davies O, Mendes P, Smallbone K, Malys N | title = Characterisation of multiple substrate-specific (d)ITP/(d)XTPase and modelling of deaminated purine nucleotide metabolism | journal = BMB Reports | volume = 45 | issue = 4 | pages = 259–264 | date = April 2012 | pmid = 22531138 | doi = 10.5483/BMBRep.2012.45.4.259 | doi-access = free }}</ref>

Defects in enzymes that control purine production and breakdown can severely alter a cell's DNA sequences, which may explain why people who carry certain genetic variants of purine metabolic enzymes have a higher risk for some types of [[cancer]].

===Purine biosynthesis in the three domains of life===

Organisms in all three domains of life, [[eukaryote]]s, [[bacteria]] and [[archaea]], are able to carry out de novo [[purine metabolism|biosynthesis of purines]]. This ability reflects the essentiality of purines for life. The biochemical pathway of synthesis is very similar in eukaryotes and bacterial species, but is more variable among archaeal species.<ref name="Brown2011">{{Cite journal |doi=10.1186/1745-6150-6-63 |pmc=3261824 |pmid=22168471|title=Purine biosynthesis in archaea: Variations on a theme |year=2011 |last1=Brown |first1=Anne M. |last2=Hoopes |first2=Samantha L. |last3=White |first3=Robert H. |last4=Sarisky |first4=Catherine A. |journal=Biology Direct |volume=6 |page=63 |doi-access=free }}</ref> A nearly complete, or complete, set of genes required for purine biosynthesis was determined to be present in 58 of the 65 archaeal species studied.<ref name = Brown2011/> However, also identified were seven archaeal species with entirely, or nearly entirely, absent purine encoding genes. Apparently the archaeal species unable to synthesize purines are able to acquire exogenous purines for growth.,<ref name = Brown2011/> and are thus analogous to purine mutants of eukaryotes, e.g. purine mutants of the Ascomycete fungus ''Neurospora crassa'',<ref>{{Cite journal |doi=10.1099/00221287-25-1-41 |doi-access=free|title=Imidazole Compounds Accumulated by Purine Mutants of Neurospora crassa |year=1961 |last1=Bernstein |first1=H. |journal=Journal of General Microbiology |volume=25 |pages=41–46 }}</ref> that also require exogenous purines for growth.

=== Relationship with gout ===

{{see also|Gout#Cause}}

Higher levels of [[meat]] and [[seafood]] consumption are associated with an increased risk of [[gout]], whereas a higher level of consumption of [[dairy product]]s is associated with a decreased risk. Moderate intake of purine-rich vegetables or protein is not associated with an increased risk of gout.<ref>{{cite journal | vauthors = Choi HK, Atkinson K, Karlson EW, Willett W, Curhan G | title = Purine-rich foods, dairy and protein intake, and the risk of gout in men | journal = The New England Journal of Medicine | volume = 350 | issue = 11 | pages = 1093–1103 | date = March 2004 | pmid = 15014182 | doi = 10.1056/NEJMoa035700 | doi-access = free }}</ref> Similar results have been found with the risk of [[Hyperuricemia#Increased production of uric acid|hyperuricemia]].

==Laboratory synthesis==

In addition to ''[[in vivo]]'' synthesis of purines in [[purine metabolism]], purine can also be synthesized artificially.

Purine ('''1''') is obtained in good yield when [[formamide]] is heated in an open vessel at 170&nbsp;°C for 28 hours.<ref name="Yamada">{{cite journal|journal=Chemical & Pharmaceutical Bulletin|year=1972|volume=20|page=623|title=A One-step Synthesis of Purine Ring from Formamide| vauthors = Yamada H, Okamoto T |doi=10.1248/cpb.20.623|issue=3| url=https://www.jstage.jst.go.jp/article/cpb1958/20/3/20_3_623/_article| archive-url=http://arquivo.pt/wayback/20160516170519/http://www.journalarchive.jst.go.jp/english/jnlabstract_en.php?cdjournal=cpb1958&cdvol=20&noissue=3&startpage=623| url-status=live| archive-date=2016-05-16|doi-access=free}}</ref>

: [[Image:Purinesynthesis-en.svg|250px]]

This remarkable reaction and others like it have been discussed in the context of [[abiogenesis|the origin of life]].<ref name="Saladino">{{cite journal | vauthors = Saladino R, Crestini C, Ciciriello F, Costanzo G, Di Mauro E | title = About a formamide-based origin of informational polymers: syntheses of nucleobases and favourable thermodynamic niches for early polymers | journal = Origins of Life and Evolution of the Biosphere | volume = 36 | issue = 5–6 | pages = 523–531 | date = December 2006 | pmid = 17136429 | doi = 10.1007/s11084-006-9053-2 | s2cid = 36278915 | bibcode = 2006OLEB...36..523S }}</ref>

Patented August 20, 1968, the current recognized method of industrial-scale production of adenine is a modified form of the formamide method. This method heats up formamide under 120 degree Celsius conditions within a sealed flask for 5 hours to form adenine. The reaction is heavily increased&nbsp; in quantity by using a phosphorus oxychloride (phosphoryl chloride) or phosphorus pentachloride as an acid catalyst and sunlight or ultraviolet conditions. After the 5 hours have passed and the formamide-phosphorus oxychloride-adenine solution cools down, water is put into the flask containing the formamide and now-formed adenine. The water-formamide-adenine solution is then poured through a filtering column of activated charcoal. The water and formamide molecules, being small molecules, will pass through the charcoal and into the waste flask; the large adenine molecules, however, will attach or “adsorb” to the charcoal due to the van der waals forces that interact between the adenine and the carbon in the charcoal. Because charcoal has a large surface area, it's able to capture the majority of molecules that pass a certain size (greater than water and formamide) through it. To extract the adenine from the charcoal-adsorbed adenine, ammonia gas dissolved in water (aqua ammonia) is poured onto the activated charcoal-adenine structure to liberate the adenine into the ammonia-water solution. The solution containing water, ammonia, and adenine is then left to air dry, with the adenine losing solubility due to the loss of ammonia gas that previously made the solution basic and capable of dissolving adenine, thus causing it to crystallize into a pure white powder that can be stored.<ref>{{Cite patent|title=Process for preparing adenine|gdate=1966-11-10|url=https://patents.google.com/patent/US3398149A/en}} {{Webarchive|url=https://web.archive.org/web/20210526024518/https://patents.google.com/patent/US3398149A/en |date=2021-05-26 }}</ref>

Oro and Kamat (1961) and Orgel co-workers (1966, 1967) have shown that four molecules of [[Hydrogen cyanide|HCN]] tetramerize to form [[diaminomaleonitrile|diaminomaleodinitrile]] ('''12'''), which can be converted into almost all naturally occurring purines.<ref>{{cite journal | vauthors = Sanchez RA, Ferris JP, Orgel LE | title = Studies in prebiotic synthesis. II. Synthesis of purine precursors and amino acids from aqueous hydrogen cyanide | journal = Journal of Molecular Biology | volume = 30 | issue = 2 | pages = 223–253 | date = December 1967 | pmid = 4297187 | doi = 10.1016/S0022-2836(67)80037-8 }}</ref><ref>{{cite journal| vauthors = Ferris JP, Orgel LE |title=An Unusual Photochemical Rearrangement in the Synthesis of Adenine from Hydrogen Cyanide|journal=Journal of the American Chemical Society|date=March 1966|volume=88|issue=5|page=1074|doi=10.1021/ja00957a050}}</ref><ref>{{cite journal | vauthors = Ferris JP, Kuder JE, Catalano AW | title = Photochemical reactions and the chemical evolution of purines and nicotinamide derivatives | journal = Science | volume = 166 | issue = 3906 | pages = 765–6 | date = November 1969 | pmid = 4241847 | doi = 10.1126/science.166.3906.765 | bibcode = 1969Sci...166..765F | s2cid = 695243 }}</ref><ref>{{cite journal | vauthors = Oro J, Kamat SS | title = Amino-acid synthesis from hydrogen cyanide under possible primitive earth conditions | journal = Nature | volume = 190 | issue = 4774 | pages = 442–3 | date = April 1961 | pmid = 13731262 | doi = 10.1038/190442a0 | bibcode = 1961Natur.190..442O | s2cid = 4219284 }}</ref><ref>{{cite book | vauthors = Bauer W |title=Houben-Weyl Methods of Organic Chemistry |volume=E 5 |edition=4th Supplement |date=1985 |publisher=Thieme Georg Verlag |isbn=978-3-13-181154-7 |page=1547}}</ref> For example, five molecules of HCN condense in an exothermic reaction to make [[adenine]], especially in the presence of ammonia.

[[Image:Basicpurines.png]]

{{anchor|Traube purine synthesis}}

The '''Traube purine synthesis''' (1900) is a classic reaction (named after [[Wilhelm Traube]]) between an [[amine]]-substituted [[pyrimidine]] and [[formic acid]].<ref>{{cite book |title=Organic Syntheses Based on Name Reactions | vauthors = Hassner A, Stumer C |publisher=Elsevier |year=2002 |edition=2nd |isbn=0-08-043259-X}}</ref>

[[Image:TraubePurineSynthesis.svg|Traube purine synthesis]]

==Prebiotic synthesis of purine ribonucleosides==

In order to understand how [[life]] arose, knowledge is required of the chemical pathways that permit formation of the key building blocks of life under plausible [[abiogenesis|prebiotic conditions]]. Nam et al. (2018)<ref>{{cite journal |vauthors=Nam I, Nam HG, Zare RN |title=Abiotic synthesis of purine and pyrimidine ribonucleosides in aqueous microdroplets |journal=Proc Natl Acad Sci U S A |volume=115 |issue=1 |pages=36–40 |date=January 2018 |pmid=29255025 |pmc=5776833 |doi=10.1073/pnas.1718559115 }}</ref> demonstrated the direct condensation of purine and pyrimidine nucleobases with ribose to give ribonucleosides in aqueous microdroplets, a key step leading to RNA formation. Also, a plausible prebiotic process for synthesizing purine ribonucleosides was presented by Becker et al. (2016).<ref>{{cite journal |vauthors=Becker S, Thoma I, Deutsch A, Gehrke T, Mayer P, Zipse H, Carell T |title=A high-yielding, strictly regioselective prebiotic purine nucleoside formation pathway |journal=Science |volume=352 |issue=6287 |pages=833–6 |date=May 2016 |pmid=27174989 |doi=10.1126/science.aad2808 }}</ref>

== See also ==

* [[Purinones]]

* [[Pyrimidine]]

* [[Simple aromatic ring]]s

* [[Transition (genetics)|Transition]]

* [[Transversion]]

* [[Gout]], a disorder of purine metabolism

*[[Adenine]]

*[[Guanine]]

== References ==

{{Reflist|30em}}

== External links ==

* [http://www.dietaryfiberfood.com/purine-food.php Purine Content in Food]

{{Nucleobases, nucleosides, and nucleotides}}

{{Purinergics}}

{{Authority control}}

[[Category:Purines| ]]

[[Category:Simple aromatic rings]]

[[Category:1898 in science]]

[[Category:Emil Fischer]]

[[Category:Substances discovered in the 19th century]]