Pyrimidine Uracil

Nitrogenous base plus sugar moiety are called nucleosides. Ribonucleic acids (RNA) resemble DNA in that nucleoside monophosphates are joined through phosphodiester bonds. RNAs differ in that the sugars are p-D-ribose units and the pyrimidine uracil is found in place of thymine. Molecular structures and nomenclature for nitrogenous bases, nucleosides, and nucleotides are delineated in Table 2.2. 

Fluorouracil (5FU) is 5-fluoropyridrimidine-2,4(1/7, 3H)-dione. Its structure is illustrated in Figure 11. The hydrogen in the naturally occurring pyrimidine, uracil, is substituted by fluorine in the 5 position. The presence of the heteroatoms in the structure imparts hydrophilicity to the compound as they are capable of hydrogen bonding. 

Bardaji, E. G. Freisinger, E. Costisella, B. SchaUey, C. A. Briining, W. Sabat, M. Lippert, B. Mixed-metal (platinum, palladium), mixed-pyrimidine (uracil, cytosine) self-assembling metaUacalix[n]arenes Dynamic combinatorial chemistry with nucleobases and metal species. Chem. Eur. J. 2007,13, 6019-6039. 

Bases, Nucleosides, and Nucleotides. The relationship of these components of a nucleic acid or polynucleotide is shown in Chart 10. The numbering of the pyrimidine (uracil) and the purine (adenine) shown is the IUPAC nomenclature used by Chemical Abstracts, and... 

Alanine occupies a central role in intermediary metabolism, primarily as the metabolic breakdown product of pyrimidine (uracil, cytidine) metabolism [7]. Increases in /1-alanine may also be detected in hyper-/ -alaninemia, GABA-T deficiency (see above), and putative combined semialdehyde dehydrogenase deficiency... 

Bovine pancreatic ribonuclease catalyzes the hydrolysis of RNA by a two-step process in which a cyclic phosphate intermediate is formed (equation 16.35). The cyclization step is usually much faster than the subsequent hydrolysis, so the intermediate may be readily isolated. DNA is not hydrolyzed, as it lacks the 2 -hydroxyl group that is essential for this reaction. There is a strong specificity for the base B on the 3 side of the substrate to be a pyrimidine—uracil or cytosine. 

Cytosine (2-hydroxy-6-amino-pyrimidine), uracil (2,6-dihydroxypyrimidine), and thymine (5-methyluracil) are pyrimidine derivatives adenine (6-aminopurine), guanine (2-amino-6-hy-droxypurine), and xanthine (2,6-dihydroxypurine) are purine derivatives (Fig. 5). 

RNA differs from DNA in three ways the sugar is D-ribose, the pyrimidine uracil replaces thymine (the other three bases are the same), and the molecules are mainly single-stranded. The three principal types of RNA are messenger RNA (involved in transcribing the genetic code), transfer RNA (which carries a specific amino acid to the site of protein synthesis), and ribosomal RNA. 

Of these pyrimidines, uracil and cytosine are constituents of ribonucleic acid, whereas thymine and cytosine are components of deoxyribonucleic acid. It was generally accepted that these nitrogenous heterocycles were the only pyrimidine components of the nucleic acids. The possibility that the nucleic acids might contain moieties other than those described had been voiced by Gulland,26 Chargaff and Vischer,27 and Davidson.28 The... 

We have now inaugurated in the Sheffield Chemical Laboratory an extended research dealing with the application of catalytic methods of reduction and oxidation to pyrimidine, purine, hydantoin and glyoxaline compounds, and in this paper, the first of our series, we record the results obtained by direct reduction of the pyrimidine uracil with colloidal platinum. 

Fluorouracil (5-FU) is a fluorinated analog of the naturally occurring pyrimidine uracil, originally synthesized in the late 1950s (Table 124—11). It is a prodrug and must be metabolized to the nucleotide form, fluorodeoxyuridine monophosphate (FdUMP), to be active. In the presence of folates, FdUMP binds tightly to and interferes with... 

It was not until tlie 1960s that it became quite clear that, in the living cell, glycogen synthesis followed quite another and more complicated route than the reversal of phosphorylase action, and that in this new pathway the equilibrium of the reaction was shifted decisively away from the sugar phosphate and towards the polymer chain formation. This breakthrough followed the discovery by Luis Leloir in Argentina of a new coenzyme derived from the pyrimidine, uracil. 

As a typical pi-deficient system, hydroxyl groups on the pyrimidine are involved in tautomeric equilibrium with the 0x0 form, and it is this form that greatly dominates in the equilibrium. Nevertheless, electrophilic substitution is easily effected on the oxopyrimidine stmcture. As an example, the diketo pyrimidine uracil (9.120) reacts readily with nitric acid to give the 5-nitro product 9.121. This suggests that the reactive species may be the hydroxyl form, albeit in a low concentration (Scheme 9.60). 

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