pyrimidine(redirected from A pyrimidine)
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pyrimidine(pīrĭm`ĭdēn'), type of organic base found in certain coenzymescoenzyme
, any one of a group of relatively small organic molecules required for the catalytic function of certain enzymes. A coenzyme may either be attached by covalent bonds to a particular enzyme or exist freely in solution, but in either case it participates intimately in
..... Click the link for more information. and in the nucleic acidsnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
..... Click the link for more information. of plant and animal tissue. The three major pyrimidines of almost universal distribution in living systems are cytosinecytosine
, organic base of the pyrimidine family. It was isolated from the nucleic acid of calf thymus tissue in 1894. A suggested structure for cytosine, published in 1903, was confirmed in the same year when that base was synthesized in the laboratory.
..... Click the link for more information. , thyminethymine
, organic base of the pyrimidine family. Thymine was the first pyrimidine to be purified from a natural source, having been isolated from calf thymus and beef spleen in 1893–94.
..... Click the link for more information. , and uraciluracil
, organic base of the pyrimidine family. It was isolated from herring sperm and also produced in a laboratory in 1900–1901. When combined with the sugar ribose in a glycosidic linkage, uracil forms a derivative called uridine (a nucleoside), which in turn can be
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A heterocyclic organic
Pyrimidine compounds which are found universally in living organisms include uracil ( 2 ), cytosine ( 3 ), and thymine( 4 ). Together with purines these substances make up the “bases” of nucleic acids, uracil and cytosine being found characteristically in ribonucleic acids, with thymine replacing uracil in deoxyribonucleic acids. A number of related pyrimidines also occur in lesser amounts in certain nucleic acids. Other pyrimidines of general natural occurrence are orotic acid and thiamine (vitamin B1). See Deoxyribonucleic acid (DNA), Purine, Ribonucleic acid (RNA)
Among the sulfa drugs, the pyrimidine derivatives, sulfadi-azine, sulfamerazine, and sulfamethazine, have general formula ( 5 ).These agents are inhibitors of folic acid biosynthesis in microorganisms. The barbiturates are pyrimidine derivatives which possess potent depressant action on the central nervous system.
(also called 1,3-diazine), a heterocyclic compound. Colorless crystals; melting point, 21°C; boiling point, 124°C. Pyrimidine is readily soluble in water, alcohol, and ether. The structural formula is
Pyrimidine is a very weak, monoacidic base that forms quaternary salts, each of which contains a single nitrogen atom; it also reacts with hydrogen peroxide (H2O2) to yield N-oxides. Pyrimidine does not enter readily into electrophilic substitution reactions, for example, halogenation, sulfonation, and nitration, but the hydrogen atom on the carbon in position number four is easily replaced in reactions with organomagnesium compounds, organolithium compounds, NaNH2, and KOH. Pyrimidine is synthesized by reduction of its 2,4,6-trichloro derivative, which is a product of the reaction of POCI3 with barbituric acid. Pyrimidine and its derivatives are components of individual nucleotides and of nucleic acids, the most important biopolymers. They also occur in many biologically active substances, including thiamine, the antibiotic, amicetin, and barbiturates.