Thymidine

{{Short description|Chemical compound}} {{Distinguish|thymine}} {{Use dmy dates|date=November 2025}} {{cs1 config|name-list-style=vanc|display-authors=6}} {{chembox | ImageFile = Desoxythymidin.svg | ImageClass = skin-invert-image | ImageSize = 180 | ImageAlt = Skeletal formula of thymidine | ImageFile1 = Thymidine 3D ball.png | ImageClass1 = bg-transparent | 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; doxribtimine; 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 | PubChem = 1134 | ChEMBL = 52609 | DrugBank = DB04485 | UNII = VC2W18DGKR | 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 = 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 = 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''' (symbol '''dT''' or '''dThd'''), also known as '''deoxythymidine''' is a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine (A) in double-stranded DNA. In cell biology it is used to synchronize the cells in G1/early S phase.{{Not in body|date=November 2025}} 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 azidothymidine (AZT), much of the world's thymidine production came from herring sperm.<ref>{{cite journal | vauthors = Ishii M, Shirae H, Yokozeki K | title = Enzymatic Production of 5-Methyluridine from Purine Nucleosides and Thymine by ''Erwinia carotovora'' AJ-2992 | journal = Agricultural and Biological Chemistry | volume = 53 | issue = 12 | pages = 3209–3218 | date = 1989 | doi = 10.1080/00021369.1989.10869860 }}</ref> Thymidine occurs almost exclusively in DNA but it also occurs in the T-loop of tRNA.{{Not in body|date=November 2025}}

== Chemistry == {{Unreferenced section|date=November 2025}}

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. It has a molecular weight of {{val|242.229|u=Da}} and a melting point of 185 °C. The stability of deoxythymidine under standard temperature and pressure (STP) is very high.

== Function == {{Unreferenced section|date=November 2025}}

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.

== Clinical significance == Thymidine is listed as a chemical teratogen.<ref>The following list of chemicals known or believed to be teratogens is drawn primarily from {{cite book | title = Dangerous Properties of Industrial Materials | edition = 7th | vauthors = Sax NI, Lewis RJ }}</ref>

===Medical use=== As a pharmaceutical drug, deoxythymidine is known by the international nonproprietary name doxribtimine.<ref>{{cite journal | vauthors = ((World Health Organization)) | year = 2022 | title = International nonproprietary names for pharmaceutical substances (INN): recommended INN: list 87 | journal = WHO Drug Information | volume = 36 | issue = 1 | hdl = 10665/352794 | hdl-access = free | author-link = World Health Organization }}</ref> Doxribtimine is a component of the medication doxecitine/doxribtimine used for the treatment of thymidine kinase 2 deficiency.<ref name="FDA 20251103">{{cite web | title=FDA approves 1st drug for thymidine kinase 2 deficiency | website=U.S. Food and Drug Administration | date=3 November 2025 | url=https://www.fda.gov/drugs/news-events-human-drugs/fda-approves-1st-drug-thymidine-kinase-2-deficiency-very-rare-mitochondrial-disease | access-date=4 November 2025}} {{PD-notice}}</ref>

=== Derivatives with diagnostic or therapeutic applications === {{More citations needed section|date=November 2025}}

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

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

Azidothymidine (AZT) – used in the treatment of HIV infection. AZT inhibits the process of reverse transcription, a critical step in the viral life cycle.

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

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-L-2′-deoxythymidine, LdT) is the unmodified "unnatural" L-enantiomer of thymidine that was used in the treatment of chronic hepatitis B.<ref>{{cite book | vauthors = Gosselin G, Pierra C, Benzaria-Prad S, Dukhan D, Cretton-Scott E, Standring D, Sommadossi JP | chapter = LDT (Telbivudine) as a potent and specific nucleoside analogue (Tyzeka™, Sebivo™) for the treatment of chronic hepatitis B | title = Collection Symposium Series | pages = 244–248 | date = 2008 | doi = 10.1135/css200810244 | isbn = 978-80-86241-29-6 }}</ref>

=== Thymidine imbalance === During growth of bacteriophage T4, an excess of thymidine availability increases mutation.<ref name="Bernstein_1972">{{cite journal | vauthors = Bernstein C, Bernstein H, Mufti S, Strom B | title = Stimulation of mutation in phage T 4 by lesions in gene 32 and by thymidine imbalance | journal = Mutation Research | volume = 16 | issue = 2 | pages = 113–119 | date = October 1972 | pmid = 4561494 | doi = 10.1016/0027-5107(72)90171-6 }}</ref><ref>{{cite journal | vauthors = DeVries JK, Wallace SS | title = Reversion of bacteriophage T4rII mutants by high levels of pyrimidine deoxyribonucleosides | journal = Molecular & General Genetics | volume = 186 | issue = 1 | pages = 101–105 | date = 1982 | pmid = 7050620 | doi = 10.1007/BF00422919 }}</ref> A deficiency of thymidine during growth also increases mutation.<ref name="Bernstein_1972" /> 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 | vauthors = Eckardt F, Kunz BA, Haynes RH | title = Variation of mutation and recombination frequencies over a range of thymidylate concentrations in a diploid thymidylate auxotroph | journal = Current Genetics | volume = 7 | issue = 5 | pages = 399–402 | date = September 1983 | pmid = 24173422 | doi = 10.1007/BF00445881 }}</ref>

== References == {{reflist}}

== External links == * {{cite web | title=Thymidine ( Code - C880 ) | website=EVS Explore | url=https://evsexplore.semantics.cancer.gov/evsexplore/concept/ncit/C880 }} * {{MeSH|D013936}}

Category:Hydroxymethyl compounds Category:Nucleosides Category:Thymine derivatives