Nucleosides, sequential

Compound 35 has also been obtained51 from 32, by sequential debenzoylation, and acetalization with 2,2-dimethoxypropane. It has been used in the synthesis, in good overall yield, of versatile, ano-merically functionalized precursors of C-nucleosides having the d-arabino or the D-ribo configuration. 

FIGURE 1 7-3 Adenosine metabolites. Adenosine is converted to inosine by adenosine deaminase. Removal of the ribose by nucleoside phos phorylase produces hypoxanthine, which is sequentially oxidized to xanthine and uric acid by xanthine oxidase. 

S. Sahabuddin, A. Roy, M. G. B. Drew, B. G. Roy, B. Achari, and S. B. Mandal, Sequential ringclosing metathesis and nitrone cycloaddition on glucose-derived substrates A divergent approach to analogues of spiroannulated carbanucleosides and conformationally locked nucleosides, J. Org. Chem., 71 (2006) 5980-5992. 

Degradation of dietary nucleic acids occurs in the small intestine, where a family of pancreatic enzymes hydrolyzes the nucleotides to nucleosides and free bases. Inside cells, purine nucleotides are sequentially degraded by specific enzymes, with uric acid as the end product of this pathway. [Note Mammals other than primates oxidize uric acid further to allantoin, which, in some animals other than mammals, may be further degraded to urea or ammonia.]... 

Several chemical and enzymatic methods are available for the synthesis of glycosyl phosphates. The required nucleoside triphosphates (NTPs) are most conveniently prepared by enzymatic routes. In general, these methods involve the sequential use of two kinases to transform NMPs to NTPs, by the corresponding NDPs (Fig. 2, see a recent review [12] for more details). 

Spleen acid exonuclease is an enzyme particularly useful in sequence studies of oligonucleotides, derived from both ribonucleic acid and deoxyribonucleic acid, since it splits off, in a sequential way, nucleoside-3 -phosphates starting from the 5 OH end. 

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). 

In principle, such processes should also be applicable to bifunctional aldehydes for a two-directional chain elongation in which two equivalents of DHAP nucleophiles would be added sequentially to both the acceptor carbonyls in a fashion that can be classified as a tandem reaction [66,67], without the need for isolation of any intermediates. Depending on the specificity of the enzyme used and on the number and position of hydroxyl functions in the starting material, the isomeric constitution, as well as the absolute and relative stereochemistry should be deliberately addressable. Thus, in a preparatively simple manner, such tandem aldolizations [68] should permit to rapidly construct larger carbohydrate molecules that would rival the carbohydrate core of tunica-mine and related nucleoside antibiotics in structural complexity. 

The syntheses of the 5 -hydrogenphosphonothioate derivatives of AZT, d4T and ddl (189a-i) have been reported. They were prepared through sequential one-pot reactions, i.e. coupling of triethylammonium phosphinate with different alcohols in the presence of pivaloyl chloride, following oxidation with elemental sulfur and further condensation with the nucleoside analogues in the presence of pivaloyl chloride. 

A series of analogues of the decamer d(GGGAATTCCC) have been prepared in which the nucleosides are sequentially replaced by (t)-butan-l,3-diol to give oligodeoxyrlbonucleotides that lack the deoxyrlbose moiety at the chosen position. The diol unit was converted into the phosphoramidite derivative... 

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