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Purine

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Title: Purine  
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Subject: Uric acid, Purine analogue, Nucleotide, Pyrimidine, Metabolism
Collection: Purines, Simple Aromatic Rings
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Purine

Purine
Skeletal formula with numbering convention
Ball-and-stick molecular model
Space-filling molecular model
Identifiers
CAS number  YesY
PubChem
ChemSpider  YesY
KEGG  YesY
MeSH
ChEBI  YesY
ChEMBL  YesY
Jmol-3D images Image 1
Properties
Molecular formula C5H4N4
Molar mass 120.11 g mol−1
Melting point 214 °C (417 °F; 487 K)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY   YesY/N?)

A purine is a pyrimidine ring fused to an imidazole ring. Purines, which include substituted purines and their tautomers, are the most widely occurring nitrogen-containing heterocycle in nature.[1]

Purines and pyrimidines make up the two groups of nitrogenous bases, including the two groups of nucleotide bases. Two of the four deoxyribonucleotides and two of the four ribonucleotides, the respective building-blocks of DNA and RNA, are purines.

Contents

  • Notable purines 1
  • Functions 2
  • History 3
  • Metabolism 4
  • Purine Sources 5
  • Laboratory synthesis 6
  • See also 7
  • References 8
  • External links 9

Notable purines

There are many naturally occurring purines. Two of the five bases in nucleic acids, adenine (2) and guanine (3), are purines. In DNA, these bases form hydrogen bonds with their complementary pyrimidines 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 (4), xanthine (5), theobromine (6), caffeine (7), uric acid (8) and isoguanine (9).

Functions

The main purine-derived nucleobases.

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 organic synthesis.

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

History

The word purine (pure urine)[2] was coined by the German chemist Emil Fischer in 1884. He synthesized it for the first time in 1899.[3] The starting material for the reaction sequence was uric acid (8), which had been isolated from kidney stones by Scheele in 1776.[4] Uric acid (8) was reacted with PCl5 to give 2,6,8-trichloropurine (10), which was converted with HI and PH4I to give 2,6-diiodopurine (11). The product was reduced to purine (1) using zinc-dust.

Metabolism

Many organisms have metabolic pathways to synthesize and break down purines.

Purines are biologically synthesized as nucleosides (bases attached to ribose).

Accumulation of modified purine nucleotides is defective to various cellular processes, especially those involving NTP and dNTP pools. Deamination of purine bases can result in accumulation of such nucleotides as ITP, dITP, XTP and dXTP.[5]

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 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.[6] Examples of high-purine sources include: sweetbreads, anchovies, sardines, liver, beef kidneys, brains, meat extracts (e.g., Oxo, Bovril), herring, mackerel, scallops, game meats, beer (from the yeast) and gravy.

A moderate amount of purine is also contained in beef, pork, poultry, other fish and seafood, asparagus, cauliflower, spinach, mushrooms, green peas, lentils, dried peas, beans, oatmeal, wheat bran, wheat germ, and hawthorn.[7]

Higher levels of meat and seafood consumption are associated with an increased risk of gout, whereas a higher level of consumption of dairy products is associated with a decreased risk. Moderate intake of purine-rich vegetables or protein is not associated with an increased risk of gout.[8][9]

Laboratory synthesis

In addition to in vivo synthesis of purines in purine metabolism, purine can also be created artificially.

Purine (1) is obtained in good yield when formamide is heated in an open vessel at 170 °C for 28 hours.[10]

This remarkable reaction and others like it have been discussed in the context of the origin of life.[11]

Oro, Orgel and co-workers have shown that four molecules of HCN tetramerize to form diaminomaleodinitrile (12), which can be converted into almost all natural-occurring purines.[12][13][14][15][16] For example, five molecules of HCN condense in an exothermic reaction to make Adenine, especially in the presence of ammonia.

The Traube purine synthesis (1900) is a classic reaction (named after Wilhelm Traube) between an amine-substituted pyrimidine and formic acid.[17]

Traube purine synthesis

See also

References

  1. ^ Rosemeyer, H. Chemistry & Biodiversity 2004, 1, 361.
  2. ^ McGuigan, Hugh (1921). An Introduction To Chemical Pharmacology. P. Blakiston's Sons & Co. p. 283. Retrieved July 18, 2012. 
  3. ^ Fischer, E. Berichte der Deutschen Chemischen Gesellschaft 1899, 32, 2550.
  4. ^ Scheele, V. Q. Examen Chemicum Calculi Urinari, Opuscula, 1776, 2, 73.
  5. ^ Davies O, Mendes P, Smallbone K, Malys N (2012). "Characterisation of multiple substrate-specific (d)ITP/(d)XTPase and modelling of deaminated purine nucleotide metabolism". BMB Reports 45 (4): 259–64.  
  6. ^ http://www.dietaryfiberfood.com/purine-food.php
  7. ^ Gout Diet: Limit High Purine Foods
  8. ^ NEJM - Purine-Rich Foods, Dairy and Protein Intake, and the Risk of Gout in Men
  9. ^ [1], USDA on bone health
  10. ^ Yamada, H.; Okamoto, T. (1972). "A One-step Synthesis of Purine Ring from Formamide". Chemical & Pharmaceutical Bulletin 20 (3): 623.  
  11. ^ Saladino et al.; Crestini, Claudia; Ciciriello, Fabiana; Costanzo, Giovanna; Mauro, Ernesto (2006). "About a Formamide-Based Origin of Informational Polymers: Syntheses of Nucleobases and Favourable Thermodynamic Niches for Early Polymers". Origins of Life and Evolution of Biospheres 36 (5–6): 523–531.  
  12. ^ Sanchez, R. A.; Ferris, J. P.; Orgel, L. E. (1967). "Studies in prebiotic synthesis. II. Synthesis of purine precursors and amino acids from aqueous hydrogen cyanide". Journal of Molecular Biology 30 (2): 223–53.  
  13. ^ Ferris, J. P.; Orgel, L. E. (1966). Journal of the American Chemical Society 88 (5): 1074.  
  14. ^ Ferris, J. P.; Kuder, J. E.; Catalano, O. W.; Kuder; Catalano (1969). "Photochemical Reactions and the Chemical Evolution of Purines and Nicotinamide Derivatives". Science 166 (3906): 765–6.  
  15. ^ Oro, J.; Kamat, J. S.; Kamat (1961). "Amino-acid Synthesis from Hydrogen Cyanide under Possible Primitive Earth Conditions". Nature 190 (4774): 442–3.  
  16. ^ Houben-Weyl, Vol . E5, p. 1547
  17. ^ Hassner, Alfred; Stumer, C. (2002). Organic Syntheses Based on Name Reactions (2nd ed.). Elsevier.  

External links

  • Purine Content in Food
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