Nucleosides 2-deoxyribo

CH2(OMe)2, CH2 = CHCH2SiMe3, MeaSiOTf, P2O5, 93-99% yield." This method was used to protect the 2 -OH of ribonucleosides and deoxyribo-nucleosides as well as the hydroxyl groups of several other carbohydrates bearing functionality such as esters, amides, and acetonides. 

This synthesis appears to be quite general for the preparation of 1-substituted nucleosides and was used with small modifications for the synthesis of l-ribofuranosyl-6-azathymine and 2 -deoxyribo-furanosyl-6-azauracil and -6-azathymine. In the case of 2 -deoxy-ribofuranosyl a mixture of a- and )8-anomers is produced, their ratio depending on the reaction conditions. In the preparation of 2 -deoxy-ribofuranosyl-6-azathymine only one anomer was obtained having probably the )8-configuration, ... 

Add 0.25 ml of DMF (./V,iV-dimethylformamide) and 0.25 ml of TRI-SIL TBT reagent to the sample in a screw-cap septum vial. If TRI-SIL TBT reagent is not readily available, add 0.25 ml of acetonitrile and 0.25 ml of BSTFA reagent instead. Heat at 60° for at least 1 hour for ribonucleosides or for a minimum of 3 hours for deoxyribo-nucleosides. After cooling to room temperature, inject 1-2 /a 1 of the reaction mixture directly into the GC. The resulting derivatives have been reported to be stable for weeks if capped tightly and refrigerated.1... 

The synthesis of purine nucleotides (1) starts from IMP. The base it contains, hypoxanthine, is converted in two steps each into adenine or guanine. The nucleoside monophosphates AMP and CMP that are formed are then phos-phorylated by nucleoside phosphate kinases to yield the diphosphates ADP and GDP, and these are finally phosphorylated into the triphosphates ATP and CTP. The nucleoside triphosphates serve as components for RNA, or function as coenzymes (see p. 106). Conversion of the ribonucleotides into deoxyribo-nucleotides occurs at the level of the diphosphates and is catalyzed by nucleoside diphosphate reductase (B). 

Scheme 9.4 Biochemical retrosynthesis of 2 -deoxyribo-nucleosides from glucose, acetaldehyde and a nucleobase (adenine) through the glycolytic pathway and the reverse reactions of 2 -deoxyribonucleoside degradation.

Scheme 9.5 Multi-step enzymatic process for 2 -deoxyribo-nucleoside production from glucose, acetaldehyde and a nucleobase through glycolysis, reverse reactions of 2 -deoxy-ribonucleoside degradation and ATP regeneration by the yeast glycolytic pathway recycling the phosphate generated by nucleoside phosphorylase.

Note Nucleoside and nucleotide are generic terns that include both ribo- and deoxyribo- fonns. Aso, ribonucleosides and ribonucleotides are here designated sinply as nucleosides and nucleotides (e.g., ribo-adenosine as adenosine), and deoxyribo-nucleosides and deoxyribonucleotides as deoxynucleosides and deoxynucleotides (e.g, deoxyribo adenosine as deoxyadeno-sine). Both fonns of nailing are acceptable, but the shortened names are more commonly used Ttynine is an exception ribotlynidine is used to describe its unusual occurrence in RNfY... 

Spleen exonuclease is active on the 5 -OH oligonucleotides of both the ribo and the deoxyribo series. These are sequentially split from the 5 -OH end with formation of 3 -mononucleotides. It has been suggested that an enzyme-product intermediate may exist in the form of nucleoside-3 -phosphoryl-enzyme complex (3) since transfer of nucleoside-3 -phosphate to available 5 -hydroxyl functions (or other alcoholic functions) occurs at high substrate (or acceptor) concentrations 15, 18). 

The term nucleoside was originally proposed by Levene and Jacobs in 1909 for the carbohydrate derivatives of purines (and, later, of pyrimidines) isolated from the alkaline hydrolyzates of yeast nucleic acid. The phosphate esters of nucleosides are the nucleotides, which, in polymerized forms, constitute the nucleic acids of all cells.2 The sugar moieties of nucleosides derived from the nucleic acids have been shown, thus far, to be either D-ribose or 2-deoxy-D-eri/fAro-pentose ( 2-deoxy-D-ribose ). The ribo-nucleosides are constituents of ribonucleic acids, which occur mainly in the cell cytoplasm whereas 2-deoxyribo -nucleosides are components of deoxypentonucleic acids, which are localized in the cell nucleus.3 The nucleic acids are not limited (in occurrence) to cellular components. They have also been found to be important constituents of plant and animal viruses. 

Four incubation mixtures are set up, each containing the DNA template, a specific DNA primer, E. coli DNA polymerase I and all four deoxyribo-nucleoside triphosphates (dNTPs). In addition, each mixture contains a different dideoxynucleoside triphosphate analog, ddATP, ddCTP ddGTP or ddTTP. Incorporation of a dideoxy analog prevents further elongation and so produces a chain termination extension product. The products are electrophoresed on a polyacrylamide gel and the DNA sequence read from the band pattern produced. 

Figure 2. Sephadex LH-20 column chromatography of DMBA-deoxyribo-nucleoside adducts formed by enzymatic digestion of DNA from mouse embryo cells exposed to [l Cj-DMBA (0.2 yg/ml) for 24 h ( - ) and of DNA from the skin of female NIH Swiss mice treated with [3h]-DMBA (10 yg/mouse) for 24 h (0-0). The arrow denotes the position of elution of an added uv-absorbing marker 4-(p-nitrobenzyl)pyridine. "Reproduced with permission from Ref. 15. Copyright 1980, IRL Press".

Polynucleotide polymerases, or nucleotidyl transferases, are enzymes that catalyze the template-instructed polymerization of deoxyribo- or ribonu-cleoside triphosphates into polymeric nucleic acid - DNA or RNA. Depending on their substrate specificity, polymerases are classed as RNA- or DNA-dependent polymerases which copy their templates into RNA or DNA (all combinations of substrates are possible). Polymerization, or nucleotidyl transfer, involves formation of a phosphodiester bond that results from nucleophilic attack of the 3 -OH of primer-template on the a-phosphate group of the incoming nucleoside triphosphate. Although substantial diversity of sequence and function is observed for natural polymerases, there is evidence that many employ the same mechanism for DNA or RNA synthesis. On the basis of the crystal structures of polymerase replication complexes, a two-metal-ion mechanism of nucleotide addition was proposed [1] during this two divalent metal ions stabilize the structure and charge of the expected pentacovalent transition state (Figure B.16.1). 

The synthesis of pteridine nucleosides from pteridones can be considered as an electrophilic attack on a ring N-atom forming an 0,iV-acetal. A large number of N-l, N-3, and N-8 substituted ribo-, 2 -deoxyribo, arabino, xylo-, and gluconucleosides have been synthesized and described silyl-method based on the Hilbert-Johnson-Birkofer reaction. Lumazine (3) reacts with hexamethyldisilazane to 2,4-bis-trimethylsilyloxypteridine (85), which condenses with l-0-acetyl-2,3,5-tri-0-benzoyl-/ -i>ribo-furanose (86) under SnCl4, BF3 or trimethylsilyl triflate catalysis to a mixture of A(-l)-mono (87),... 

The Af-glycosylpurines or purine nucleosides include many naturally occurring compounds, especially 9-/3-D-ribofuranosyl and 9-/3-D-2-deoxyribofuranosyl derivatives of adenine and guanine which are of course major constituents of the various ribo (RNA) and deoxyribo (DNA) nucleic acids. The literature on purine nucleoside chemistry is very substantial and in this chapter it will only be possible to give a brief survey. However several reviews exist (see Table 2). 

Nakagawa, 1, Hata, T, A convenient method for the synthesis of 5 -5-alkylthio-5 -deoxyribo-nucleosides, Tetrahedron Lett., 16, 1409-1412, 1975. 

A clean separation of the 4 main nucleosides (either ribo- or deoxyribo-) on cross-linked Dextran (Sephadex G-10) has been described by Braun (1967b). He used a 1.5x90 cm column eluted with 0.01 M citric acid Na2HP04, pH 3.5 at 25 ml/hr. The sample was loaded in 0.5 ml water and contained 0.1 mg of each nucleoside. The elution took 10 hr and each nucleoside was eluted in a volume of 10-20 ml in the order, C, U, A, G or C, T, A, G for the... 

By removing an oxygen (O), the enzyme ribonucleotide reductase creates deoxyribo-nucleosides, the building blocks of DNA. 

Small amounts of purine ribonucleosides and deoxyribo -nucleosides can be prepared enzymically. Two types of enzyme have been found that catalyze the synthesis of nucleosides. The first are the nucleoside phos-phorylases, which catalyze the reaction of purines and D-ribosyl phosphate or 2-deoxy- D-ribosyl phosphate as follows. 

Tris(hexafluoroisopropyl) phosphite (105) has been used to prepare ribonucleoside H-phosphonates (106), and deoxyribo-nucleoside phosphites (107) ° both were used as monomers to prepare oligonucleoside H-phosphonates on a solid support, with W-methylimidazole as catalyst for the coupling of (107). Several new alkyl phosphorodiamidites (108) and (109) have been used... 

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