Pyrimidine (redirected from A pyrimidine)

pyrimidine (pīrĭm`ĭdēn'), type of organic base found in certain coenzymes and in the nucleic acids of plant and animal tissue. The three major pyrimidines of almost universal distribution in living systems are cytosine, thymine, and uracil.

---

pyrimidine

Any of a class of heterocyclic compounds with a ring structure of four carbon and two nitrogen atoms. The simplest member, pyrimidine itself (C₄H₄N₂), is not common, but derivatives with the structure are. Examples include thiamine (vitamin B₁), several sulfa drugs, barbiturates, and three of the bases in nucleic acids (cytosine, thymine, and uracil).

---

pyrimidine [pə′rim·ə‚dēn]

(biochemistry)

C₄H₄N₂A heterocyclic organic compound containing nitrogen atoms at positions 1 and 3; naturally occurring derivatives are components of nucleic acids and coenzymes.

---

Pyrimidine

A heterocyclic organic

(2)

compound ( 1 ) containing nitrogen atoms at positions 1 and 3. Naturally occurring derivatives of the parent compound are of considerable biological importance as components of nucleic acids and coenzymes and, in addition, synthetic members of this group have found use as pharmaceuticals. See Coenzyme, Nucleic acid

Pyrimidine compounds which are found universally in living organisms include uracil ( 2 ), cytosine ( 3 ), and thymine

(3)

( 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 ).

(4)

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.

---

Pyrimidine 

(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.