Nucleoside chemistry

Some examples in the area of nucleoside chemistry are the reductions of bromide 10, chloride 11, and selenide 12 in 94, 92, and 87% yields, respectively, at 80 °C using AIBN as the radical initiator.Multiple dehalogenations are possible in a one-pot procedure by using the corresponding equivalents of (TMSlsSiH. ... 

Peroxydisulfate was also reported as a reagent in nucleoside chemistry. Interestingly, the etheno bridge of l,V -ethenoadenosine can be smoothly removed by treatment with potassium peroxydisulfate (equation 20). ... 

The synthesis of 3-nitro-l-substituted uracil derivatives 30 can readily be performed with trifluoroacetic nitric anhydride, and this procedure is used in nucleoside chemistry to convert the uracil 3-nitrogen to a good leaving group <1995JA3665, 1997JOC1547, 20020L1827>. 

Takatsuki and co-workers have recently introduced the 3, 5 -0-sulfinyl group which has the dual purpose of protection and activation in nucleoside chemistry. For example, compound 13, prepared by protection of 12 as shown in Scheme 3, underwent reaction with benzyl isocyanate followed by intramolecular displacement of the sulfmate to give the product 14 <2004TL137>. A similar approach has also been used to prepare thioglycoside epoxides <2004CAR2895>. 

Acetic anhydride also provides a substantial acceleration of PDC oxidations, which is particularly useful in sugar and nucleoside chemistry.129... 

In this respect, some recent reports on the radical reduction of pharmaceutically relevant compounds showed the efficiency and effectiveness of this reagent. Here below we describe some examples in the field of nucleoside chemistry. 

Although this review deals with the pyrimidine nucleosides, it will be necessary to refer occasionally to their purine counterparts. The authors take into account the previous reviews in this series by Tipson,10 Jeanloz and Fletcher,11 and Barker,12 which have dealt in greater or lesser degree with this subject. Some recounting of earlier work in the field of nucleoside chemistry will be necessary, in order to place newer developments in proper historical context. 

All in all, these anhydronucleoside studies represent an exciting advance in the field of pyrimidine-nucleoside chemistry. Aside from the achievement... 

Other reviews are available dealing with specialized purine topics, which include their general chemistry,1 synthesis from pyrimidines2 and imidazoles,3 biological synthesis,4 and nucleoside chemistry.5... 

The marked stereoselectivity of these radical reactions must be ascribed to the effect of the bulk of the protecting groups. However, the radicals that were manipulated may have also shown an anomeric effect due to the vicinal oxygen. In a furanose sugar it is not easy to evaluate the anomeric effect without ESR, and also, the molecules concerned have two fused five-membered rings. This fixes the conformation into a V-shape. Such molecules are well known to have exo-reactivity and the formation of endo-bonds is difficult. All these effects may be acting together to make this nucleoside chemistry especially stereospecific. 

Quite apart from these experimental advances, Zorbach made a major contribution to nucleoside chemistry in conceiving the idea of a series of volumes devoted to Synthetic Procedures in Nucleic Acid Chemistry and, together with R. S. Tipson as co-editor, bringing to final form a first volume that is indispensable to all workers in this area, as it assembles and summarizes the optimal methods that had been developed up to 1968. The manuscripts for the second volume, describing physical and physicochemical techniques used in the characterization and structural determination of nucleosides, nucleotides, and related compounds were sent to the publisher just a few months before Zorbach s death. 

Heteroaryl halides such as halopyridines, bromoquinolines " , furyl halides , thienyl halides and imidazolyl bromides " were found to be reactive. A particularly interesting application concerns nucleoside chemistry, since 2-iodopurine " 246 5-iodouridine , 5-halouracil2 ° 2 and 5-iodocytosine were used successfully. When the reactivity of the carbon-halogen bond is exalted, the coupling reaction can be extended to chloro derivatives, such as 6-chloropurines ", 4- and 5-chloro-pyrimidines and 2-chloropyrazines °. 

In recent years biotransformations have also shown their potential when applied to nucleoside chemistry [7]. This chapter will give several examples that cover the different possibiUties using biocatalysts, especially lipases, in order to synthesize new nucleoside analogs. The chapter will demonstrate some applications of enzymatic acylations and alkoxycarbonylations for the synthesis of new analogs. The utQity of these biocatalytic reactions for selective transformations in nucleosides is noteworthy. In addition, some of these biocatalytic processes can be used not only for protection or activation of hydroxyl groups, but also for enzymatic resolution of racemic mixtures of nucleosides. Moreover, some possibilities with other biocatalysts that can modify bases, such as deaminases [8] or enzymes that catalyze the synthesis of new nucleoside analogs via transglycosylation [9] are also discussed. 

As modified oligonucleotides have become a major field of investigation for chemists, methods for the suitable protection/deprotection applied to the synthesis of nucleoside monomers have become equally important. Selective protection of a multifunctional compound is a challenging problem in organic synthesis. In nucleoside chemistry, selective manipulation of the hydroxyl groups on the carbohydrate moiety over amino groups of the bases is synthetically challenging and... 

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). 

Many examples of compounds in which a heterocyclic ring is fused to a purine have been recorded. These include the various types of cyclonucleosides such as (210). However in this chapter a discussion of these compounds is not practical and for further details the reader should consult works devoted to nucleoside chemistry. Appropriate references are collected in Table 2. 

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