Ribose nucleosides

Nature of the Bases. The bases were readily, and hence early, identified as the purines adenine and guanine and the pyrimidines cytosine and uracil. They were isolated first by complete hydrolysis of nucleic acid, and later from the individual nucleosides. Levene showed that the two purine and the two pyrimidine bases occur in ribosenucleic acid in equimolecular proportions, and for the purines this conclusion has been confirmed.  

As regards the next four details of structure, let us first consider the purine nucleosides from ribosenucleic acid. 

The purine nucleosides from ribosenucleic acid are adenosine and guanosine. Historically, guanosine was the first ribose nucleoside to be discovered, having been isolated from plant extracts by Schulze in 1885 and named vernine. In 1909 it was prepared from ribosenucleic acid by Levene and Jacobs, who also isolated adenosine from the same source. These two nucleosides are readily hydrolyzed by dilute mineral acid to give the respective bases and the same sugar. 

Gulland and coworkers recently confirmed the finding that the sugar component of the four mononucleotides of yeast pentosenucleic acid is D-ribose through the isolation of D-ribonic benzimidazole and they also reported that a small amount of L-lyxonic benzimidazole was detected how this latter result is to be interpreted is not yet clear. 

Stereochemical Configuration. Deamination by means of nitrous acid transforms adenosine into inosine - (ribosyl-hypoxanthine), and guanosine into xanthosine - - (ribosyl-xanthine). These four purine nucleosides are hydrolyzed rapidly, and with equal ease, by dilute mineral acids. They are also all hydrolyzed by the same enzyme, so it is reasonable to presume that they are similarly constituted as regards the stereochemical disposition at the sugar-base link. Whether this is of the a- or 

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Arabinose is an epimer of ribose. Nucleosides in which arabinose is substituted for ribose act as inhibitors in reactions of ribonucleosides. 

Jardetzky CD, Jardetzky O (1960) Investigation of the structure of purines, pyrimidines, ribose nucleosides and nucleotides by proton magnetic resonance.il. J Am Chem Soc... 

Amino-4-imidazole carboxamide ribotide, a precursor only two steps removed (formylation and cycli-zation) from inosinic acid, can be synthesized by the direct condensation of the imidazole with 5-phosphori-bosyl pyrophosphate. The enzyme catalyzing this reaction was purified from an acetone powder of beef liver. The same enzyme (AMP pyrophosphorylase) catalyzes the condensation of adenine, guanine, and hypoxan-thine. Nucleoside phosphorylase is an enzyme that catalyzes the formation of a ribose nucleoside from a purine base and ribose-1-phosphate. Guanine, adenine, xanthine, hypoxanthine, 2,6-diaminopurine, and aminoimidazole carboxamide are known to be converted to their respective nucleosides by such a mechanism. In the presence of a specific kinase and ATP, the nucleoside is then phosphorylated to the corresponding nucleotide. 

The numbering scheme used for nucleosides maintains the independence of the two structural units The pyrimidine or purine is numbered m the usual way So is the car bohydrate except that a prime symbol ( ) follows each locant Thus adenosine is a nude oside of D nbose and 2 deoxyadenosine is a nucleoside of 2 deoxy d ribose... 

The same kind of 5 3 phosphodiester units that join the 2 deoxy d ribose units m Figure 28 I are also responsible for connecting nucleosides of d ribose... 

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... 

Nucleoside (Section 28 2) The combination of a purine or pynmidme base and a carbohydrate usually ribose or 2 deoxynbose... 

Nucleic Acids. Phosphoms is an essential component of nucleic acids, polymers consisting of chains of nucleosides, a sugar plus a nitrogenous base, and joined by phosphate groups (43,44). In ribonucleic acid (RNA), the sugar is D-ribose in deoxyribonucleic acids (DNA), the sugar is 2-deoxy-D-ribose. 

DiaZepin Nucleosides. Four naturally occurring dia2epin nucleosides, coformycin (58), 2 -deoxycoformycin (59), adechlorin or 2 -chloro-2 -deoxycoformycin (60), and adecypenol (61), have been isolated (1—4,174,175). The biosynthesis of (59) and (60) have been reported to proceed from adenosine and C-1 of D-ribose (30,176,177). They are strong inhibitors of adenosine deaminase and AMP deaminase (178). Compound (58) protects adenosine and formycin (12) from deamination by adenosine deaminase. Advanced hairy cell leukemia has shown rapid response to (59) with or without a-or P-interferon treatment (179—187). In addition, (59) affects interleukin-2 production, receptor expression on human T-ceUs, DNA repair synthesis, immunosuppression, natural killer cell activity, and cytokine production (188—194). 

The most important nucleosides are derived from D-ribose and 2-deoxy-D-ribose. 

A stereospecific total synthesis of polyoxin C and related nucleosides is reported, in which thereacdon of l-Cphenylthioi-l-nitroalkenes v/ith nucleophiles and siibseqiientozono lysis are key reacdons Addidonof potassium trimethylsilanoate to l-Cphenylthioi-nitroalkenes derived from D-ribose followed by ozonolysis gives the cr-hydroxy thioester, which is formed v/ith excellent diastereoselecdvity fScheme 4 5 This conformadon meets the stereo-electronic requirements for andperiplanar addition of the nucleophile with the result of high 5-fS stereochemical bias in the reacdons... 

The nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are biological polymers that act as chemical carriers of an organism s genetic information. Enzyme-catalyzed hydrolysis of nucleic acids yields nucleotides, the monomer units from which RNA and DNA are constructed. Further enzyme-catalyzed hydrolysis of the nucleotides yields nucleosides plus phosphate. Nucleosides, in turn, consist of a purine or pyrimidine base linked to Cl of an aldopentose sugar—ribose in RNA and 2-deoxyribose in DNA. The nucleotides are joined by phosphate links between the 5 phosphate of one nucleotide and the 3 hydroxyl on the sugar of another nucleotide. 

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