Isocytosine

Isocytosine

Names
Preferred IUPAC name 2-Amino-3H-pyrimidin-4-one
Other names 2-Aminouracil
Identifiers
CAS Number	108-53-2  Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:55502  Y
ChEMBL	ChEMBL56260  Y
ChemSpider	60309  Y
ECHA InfoCard	100.003.266
PubChem CID	66950
CompTox Dashboard (EPA)	DTXSID00148350
InChI InChI=1S/C4H5N3O/c5-4-6-2-1-3(8)7-4/h1-2H,(H3,5,6,7,8) Y Key: XQCZBXHVTFVIFE-UHFFFAOYSA-N Y InChI=1/C4H5N3O/c5-4-6-2-1-3(8)7-4/h1-2H,(H3,5,6,7,8) Key: XQCZBXHVTFVIFE-UHFFFAOYAD
SMILES O=C1/C=C\N=C(\N)N1
Properties
Chemical formula	C4H5N3O
Molar mass	111.104 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y  verify  (what is  YN ?) Infobox references

Isocytosine or 2-aminouracil is a pyrimidine base that is an isomer of cytosine. The nucleoside form is called isocytidine (iC). ^[1]

It is used in combination with isoguanine in studies of unnatural nucleic acid analogues of the normal base pairs in DNA. ^[2] In particular, it is used as a nucleobase of hachimoji RNA with the abbreviation rS. ^[3]

Isoguanine-Isocytosine-base-pair

Synthesis

It can be synthesized from guanidine and malic acid. ^[4]

Synthesis of isocytosine from malic acid

Isocytosine can also be obtained by condensing guanidine hydrochloride with 3-oxopropanoic acid. However, the C₃ component is not storable in this case and was, therefore, replaced with malic acid. This is decarbonylated in concentrated sulfuric acid with elimination of water, thus losing carbon monoxide. The 3-oxopropanoic acid formed in situ condenses with the guanidine in the sulfuric acid solution with double elimination of water. ^[5]

Uses

It is also used in physical chemical studies involving metal complex binding, hydrogen bonding, and tautomerism and proton transfer effects in nucleobases. ^[6]

Tautomerism of isocytosine

References

1. Hopfinger, MC; Kirkpatrick, CC; Znosko, BM (18 September 2020). "Predictions and analyses of RNA nearest neighbor parameters for modified nucleotides". Nucleic Acids Research. 48 (16): 8901–8913. doi:10.1093/nar/gkaa654. PMC   7498315 . PMID   32810273.
2. "Isocytosine". Molecule of the Week. American Chemical Society . Retrieved November 1, 2012.
3. Hoshika, Shuichi; et al. (22 February 2019). "Hachimoji DNA and RNA: A genetic system with eight building blocks". Science . 363 (6429): 884–887. Bibcode:2019Sci...363..884H. doi:10.1126/science.aat0971. PMC   6413494 . PMID   30792304.
4. William T. Caldwell , Harry B. Kime (1940). "A New Synthesis of Isocytosine". J. Am. Chem. Soc. 62 (9): 2365. Bibcode:1940JAChS..62.2365C. doi:10.1021/ja01866a028.
5. Caldwell, William T.; Kime, Harry B. (1 September 1940). "A New Synthesis of Isocytosine" . Journal of the American Chemical Society . 62 (9): 2365. Bibcode:1940JAChS..62.2365C. doi:10.1021/ja01866a028. ISSN   0002-7863 . Retrieved 17 June 2025.
6. "Isocytosine". Sigma-Aldrich . Retrieved November 1, 2012.