Glycosidation purine

RNA is relatively resistant to the effects of dilute acid, but gentle treatment of DNA with 1 mM HCl leads to hydrolysis of purine glycosidic bonds and the loss of purine bases from the DNA. The glycosidic bonds between pyrimidine bases and 2 -deoxyribose are not affected, and, in this case, the polynucleotide s sugar-phosphate backbone remains intact. The purine-free polynucleotide product is called apurinic acid. 

Vida faba. The Mediterranean plant Vida faba is a source of fava beans that contain the purine glycoside vicine. [Inga Spence/ Visuals Unlimited.]... 

The purine glycosides adenine and guanine are constituents of the nucleic acids of all living beings. Their phosphate esters play an important role in metabolism as energy-rich compounds (C 1.1). 

Purine derivatives Pyrrolopyrimidines, e.g., tubercidin, toyocamycin, viomycin, and purine glycosides with unusual sugar moieties, e.g., cordycepin psicofuranin, decoyinin (D 10.4) Inhibitors of nucleic acid biosynthesis... 

Scheme 1.46). The groups of Qu and Guo recently applied our method of the di-TBP mediated alleviation to various purines and purine glycosides with cycloalkanes. ... 

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... 

Note Flavonoids react with the reagent even at room temperature [1] mycotoxins, steroids, purines, pyrimidines, cardiac glycosides and lipids only react on heating [2, 4-6]. Zirconyl sulfate can be used to replace the zirconyl chloride in the reagent this is reported to result in an increase in the sensitivity to certain groups of substances (e.g. cholesteryl esters, triglycerides) [4]. 

Nucleosides are much more water-soluble than the free bases because of the hydrophilicity of the sugar moiety. Like glycosides (see Chapter 7), nucleosides are relatively stable in alkali. Pyrimidine nucleosides are also resistant to acid hydrolysis, but purine nucleosides are easily hydrolyzed in acid to yield the free base and pentose. 

Most nucleosides contain D-ribose or 2-deoxy-D-ribose linked to N-1 of a pyrimidine or to N-9 of a purine by a P-glycosidic bond whose syn conformers predominate. 

Figure 35-1. A segment of one strand of a DNA molecule in which the purine and pyrimidine bases guanine (G), cytosine (C), thymine (T), and adenine (A) are held together by a phosphodiester backbone between 2 -de-oxyribosyl moieties attached to the nucleobases by an W-glycosidic bond. Note that the backbone has a polarity (ie,a direction). Convention dictates that a single-stranded DNA sequence is written in the 5 to 3 direction (ie, pGpCpTpA, where G, C,T, and A represent the four bases and p represents the interconnecting phosphates).

The depurination of DNA, which happens spontaneously owing to the thermal lability of the purine N-glycosidic bond, occurs at a rate of 5000-10,000/cell/d at 37 °C. Specific enzymes recognize a depurinated site and replace the appropriate purine directly, without interruption of the phosphodiester backbone. 

Davoll, J., Lythgoe, B., Todd, A.R. (1946) Experiments on the Synthesis of Purine Nucleosides. Part XII. The Configuration of the Glycosidic Centre in Natural aud Syuthetic Pyrimidine and Purine Nucleosides. Journal of the Chemical Society, 833-838. 

Hydrolytic cleavage of the glycosidic bond holding the DNA bases to the sugar-phosphate backbone is typically a very slow process under physiological conditions (pH 7.4 37°C). Loss of the pyrimidine bases cytosine and thymine occurs with a rate constant of 1.5 X 10 s (ty2 = 14,700 years), while loss of the purine bases guanine and adenine proceeds slightly faster, with a rate constant of 3.0 X... 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

C5 , then the atom is said to be endo, and if it is on the opposite side it is defined as exo. The conformation about the sugar-base linkage is defined as anti when the torsion angle (chi, 04 -Cl -Nl -C2 for pyrimidines and 041-Cl -N9-C4 for purines) lies near 180° and syn when it lies near 0°. These situations are illustrated in Figure 22. The glycosidic linkage are all anti in B-DNA and A-DNA, but in Z-DNA the guanine bases are in the syn conformation. 

Figure 1.49 The structures of the common purine bases of RNA and DNA. The associated sugar groups are bound in N-glycosidic linkages to the N-9 position.

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