Of pyrimidine

This has been the subject of many investigations starting from thiamine itself or derivatives, with the aim of explaining the role of pyrimidine group in coenzymatic activity. 

The most important derivatives of pyrimidines and purines are nucleosides Nucleosides are N glycosides m which a pyrimidine or purine nitrogen is bonded to the anomeric carbon of a carbohydrate The nucleosides listed m Table 28 2 are the mam building blocks of nucleic acids In RNA the carbohydrate component is d ribofuranose m DNA It IS 2 deoxy d ribofuranose... 

Section 28 2 Nucleosides are carbohydrate derivatives of pyrimidine and purine bases The most important nucleosides are derived from d ribose and 2 deoxy D ribose... 

Antimetabolites may be further classified as inhibitors of pyrimidine, purine, or glutamine metaboHsm. The compounds are cell cycle dependent. 

The structure of pyrimidines with two or more tautomeric groups... 

Alkylation of pyrimidin-2(or 4)-amine on a ring-nitrogen gives an imine, e.g. (8), of quite high basic strength (pjSTa 10.7) because its cation, e.g. (13 R = Me), has typical and effective resonance stabilization indeed, methylation of pyrimidine-2,4-diamine gives a still stronger base (pjSTa> 13) due to an even more resonance-stabilized cation (14). 

The NMR spectra of pyrimidines bearing tautomeric groups (NH2, OH, SH) in the 2-, 4- or 6-position are discussed in connexion with the tautomerism of such pyrimidines (Section 2.13.1.8). 

Since IR spectra are essentially due to vibrational transitions, many substituents with single bonds or isolated double bonds give rise to characteristic absorption bands within a limited frequency range in contrast, the absorption due to conjugated multiple bonds is usually not characteristic and cannot be ascribed to any particular grouping. Thus IR spectra afford reference data for identification of pyrimidines, for the identification of certain attached groups and as an aid in studying qualitatively the tautomerism (if any) of pyrimidinones, pyrimidinethiones and pyrimidinamines in the solid state or in non-protic solvents (see Section 2.13.1.8). 

The UV absorption of pyrimidine occurs in two bands centred at 243 and 298 nm in cyclohexane. The second band is ascribed to the electronic transition from a nitrogen lone pair non-bonding orbital to an empty ring tt-orbital, in short an n transition, on... 

The mass spectra of pyrimidines and quinazolines are generally simple and of no great interest, factors which account for the paucity of data available (B-71MS468). 

The dominant fragmentation mode of pyrimidine is loss of HCN twice, to give ionized acetylene, m/e 26, as base peak whether C-2 or C-4 is involved in the initial loss of HCN... 

Much of the reactivity shown by the ring atoms and substituents of pyrimidine is akin to that of the corresponding parts of 1,3-dinitrobenzene and 3-nitropyridine. This arises from the quantitatively similar electron-withdrawing effects of doubly-bound ring nitrogen atoms and of nitro groups in reducing sharply the aromaticity of the cyclic system. 

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