Editing Thymidine

{{short description|Chemical compound}}
{{Distinguish|thymine}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 416414982
| ImageFile = Desoxythymidin.svg
| ImageSize = 180
| ImageAlt = Skeletal formula of thymidine
| ImageFile1 = Thymidine 3D ball.png
| ImageSize1 = 210
| ImageAlt1 = Ball-and-stick model of the thymidine molecule
| IUPACName = Thymidine
| SystematicName = 1-[(2''R'',4''S'',5''R'')-4-Hydroxy-5-(hydroxymethyl)oxolan-2-yl]-5-methylpyrimidine-2,4(1''H'',3''H'')-dione
| OtherNames=Deoxythymidine, Td, dT, 1-[(2''R'',4''S'',5''R'')-4-Hydroxy-5-(hydroxymethyl)tetrahydrofur-2-yl]-5-methyl-1,3-dihydropyrimidine-2,4-dione
|Section1={{Chembox Identifiers
| IUPHAR_ligand = 4718
| CASNo=50-89-5
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem=1134
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 52609
| DrugBank_Ref = {{drugbankcite|changed|drugbank}}
| DrugBank = DB04485
| UNII_Ref = {{fdacite|changed|FDA}}
| UNII = VC2W18DGKR
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = 5585
| SMILES = Cc1cn(c(=O)[nH]c1=O)[C@H]2C[C@@H]([C@H](O2)CO)O
| InChI = 1/C10H14N2O5/c1-5-3-12(10(16)11-9(5)15)8-2-6(14)7(4-13)17-8/h3,6-8,13-14H,2,4H2,1H3,(H,11,15,16)/t6-,7+,8+/m0/s1
| InChIKey = IQFYYKKMVGJFEH-XLPZGREQBQ
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/C10H14N2O5/c1-5-3-12(10(16)11-9(5)15)8-2-6(14)7(4-13)17-8/h3,6-8,13-14H,2,4H2,1H3,(H,11,15,16)/t6-,7+,8+/m0/s1
| StdInChIKey_Ref = {{stdinchicite|changed|chemspider}}
| StdInChIKey = IQFYYKKMVGJFEH-XLPZGREQSA-N

| MeSHName=Deoxythymidine}}
|Section2={{Chembox Properties
| C=10 | H=14 | N=2 | O=5
| Appearance=
| Density=
| MeltingPt= 185 °C
| BoilingPt=
| Solubility=
  }}
|Section3={{Chembox Hazards
| MainHazards=
| FlashPt=
| AutoignitionPt =
  }}
}}

'''Thymidine''' ([[nucleoside#List of nucleosides and corresponding nucleobases|symbol]] '''dT''' or '''dThd'''), also known as '''deoxythymidine''', '''deoxyribosylthymine''', or '''thymine deoxyriboside''', is a [[pyrimidine]] [[nucleoside|deoxynucleoside]].  Deoxythymidine is the [[DNA]] [[nucleoside]] T, which pairs with [[deoxyadenosine]] (A) in double-stranded DNA. In cell biology it is used to [[cell synchronization|synchronize]] the cells in G1/early S phase. 
The prefix '''deoxy-''' is often left out since there are no precursors of thymine nucleotides involved in RNA synthesis.

Before the boom in thymidine use caused by the need for thymidine in the production of the [[antiretroviral drug]] [[Zidovudine|azidothymidine]] (AZT), much of the world's thymidine production came from [[herring]] sperm.<ref>{{cite journal | doi=10.1080/00021369.1989.10869860 | title=Enzymatic Production of 5-Methyluridine from Purine Nucleosides and Thymine by ''Erwinia carotovora'' AJ-2992 | date=1989 | last1=Ishii | first1=Makoto | last2=Shirae | first2=Hideyuki | last3=Yokozeki | first3=Kenzo | journal=Agricultural and Biological Chemistry | volume=53 | issue=12 | pages=3209–3218 }}</ref> Thymidine occurs almost exclusively in DNA but it also occurs in the [[T arm|T-loop]] of [[tRNA]].

== Structure and properties ==
In its composition, deoxythymidine is a [[nucleoside]] composed of [[deoxyribose]] (a pentose [[sugar]]) joined to the [[pyrimidine]] base [[thymine]].

Deoxythymidine can be phosphorylated with one, two or three phosphoric acid groups, creating [[dTMP]] ('''d'''eoxy'''t'''hymidine '''m'''ono'''p'''hosphate), [[dTDP]], or [[dTTP]] (for the '''d'''i- and '''t'''ri- phosphates, respectively).

It exists in [[solid]] form as small white [[crystals]] or white crystalline [[Powder (substance)|powder]]. It has a [[molecular weight]] of {{val|242.229|u=Da}} and a [[melting point]] of 185&nbsp;[[degrees Celsius|°C]]. The stability of deoxythymidine under [[standard temperature and pressure]] (STP) is very high.

Deoxythymidine is non-toxic and is part of one of the four nucleosides in DNA. It is a naturally occurring compound that exists in all living organisms and DNA viruses. Instead of thymidine, RNA contains [[uridine]] ([[uracil]] joined to [[ribose]]). Uracil is chemically very similar to thymine, which is also known as 5-methyluracil. Since thymine nucleotides are precursors of DNA (but not RNA), the prefix "deoxy" is often left out, i.e., deoxythymidine is often just called thymidine.

Thymidine is listed as a chemical [[teratogen]].<ref>The following list of chemicals known or believed to be teratogens is drawn primarily from Dangerous Properties of Industrial Materials, 7th Ed., by N. Irving Sax and Richard J. Lewis.</ref>

== Modified analogs ==

[[Iododeoxyuridine]] is a radiosensitizer and increases the amount of DNA damage received from ionizing radiation.

[[Zidovudine|Azidothymidine]] (AZT) – used in the treatment of [[HIV]] infection.  AZT [[Reverse-transcriptase inhibitor|inhibits the process of reverse transcription]], a critical step in the [[HIV#Replication cycle|viral life cycle]].

[[Radioactive tracer|Radiolabeled]] thymidine (TdR), such as [[tritium|tritiated]] thymidine (<sup>3</sup>H-TdR), is commonly used in cell proliferation assays. The thymidine is incorporated into dividing cells and the level of this incorporation, measured using a [[Scintillation counter|liquid scintillation counter]], is proportional to the amount of cell proliferation. For example, [[lymphocyte]] proliferation can be measured this way in [[lymphoproliferative disorders]].

[[Bromodeoxyuridine]] (BrdU) is another thymidine analog that is often used for the detection of proliferating cells in living tissues.

[[5-Ethynyl-2'-deoxyuridine|5-Ethynyl-2´-deoxyuridine]] (EdU) is a thymidine analog which is incorporated into the DNA of dividing cells and is used to assay DNA synthesis in cell culture or living tissues. It can be visualized by covalently binding a fluorescent azide using [[click chemistry]], which is less harsh than the conditions used to expose the [[epitope]] for BrdU antibodies.

[[Edoxudine]] is an [[antiviral drug]].

[[Telbivudine]] (β-<small>L</small>-2′-deoxythymidine, LdT) is the unmodified "unnatural" <small>L</small>-[[enantiomer]] of thymidine that was used in the treatment of chronic [[hepatitis B]].<ref>{{cite book |doi=10.1135/css200810244|isbn=978-80-86241-29-6 |chapter=LDT (Telbivudine) as a potent and specific nucleoside analogue (Tyzeka™, Sebivo™) for the treatment of chronic hepatitis B |title=Collection Symposium Series |date=2008 |last1=Gosselin |first1=Gilles |last2=Pierra |first2=Claire |last3=Benzaria-Prad |first3=Samira |last4=Dukhan |first4=David |last5=Cretton-Scott |first5=Erika |last6=Standring |first6=David |last7=Sommadossi |first7=Jean-Pierre |pages=244–248 }}</ref>

== Thymidine imbalance induces mutation and recombination ==
During growth of [[Escherichia virus T4 |bacteriophage T4]], an excess of thymidine availability increases [[mutation]].<ref name = Bernstein1972>{{cite journal | doi=10.1016/0027-5107(72)90171-6 | title=Stimulation of mutation in phage T4 by lesions in gene 32 and by thymidine imbalance | date=1972 | last1=Bernstein | first1=Carol | last2=Bernstein | first2=Harris | last3=Siraj | first3=Mufti | last4=Barbara | first4=Strom | journal=Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis | volume=16 | issue=2 | pages=113–119 }}</ref><ref>{{cite journal | doi=10.1007/BF00422919 | title=Reversion of bacteriophage T4rIImutants by high levels of pyrimidine deoxyribonucleosides | date=1982 | last1=De Vries | first1=Joanne K. | last2=Wallace | first2=Susan S. | journal=Molecular and General Genetics | volume=186 | pages=101–105 }}</ref>  A deficiency of thymidine during growth also increases mutation.<ref name = Bernstein1972/>  A thymidylate auxotroph of the diploid yeast ''Saccharomyces cerevisiae'' was grown under conditions in which thymidyate levels varied from excess to depletion.<ref>{{cite journal | doi=10.1007/BF00445881 | title=Variation of mutation and recombination frequencies over a range of thymidylate concentrations in a diploid thymidylate auxotroph | date=1983 | last1=Eckardt | first1=Friederike | last2=Kunz | first2=Bernard A. | last3=Haynes | first3=Robert H. | journal=Current Genetics | volume=7 | issue=5 | pages=399–402 | pmid=24173422 }}</ref>  High levels of thymidylate were observed to be mutagenic and recombinogenic, whereas starvation for thymidylate was recombinogenic but only slightly mutagenic.

== References ==
{{reflist}}

== External links ==
* http://money.cnn.com/magazines/fortune/fortune_archive/1990/11/05/74308/index.htm

{{Nucleobases, nucleosides, and nucleotides}}

[[Category:Nucleosides]]
[[Category:Pyrimidinediones]]
[[Category:Hydroxymethyl compounds]]