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Abstract

This chapter presents selected methods for preparation of 2ˊ-C-, 3ˊ-C- and 4ˊ-C-branched nucleosides, followed by an account of the results. Only synthesis of analogues having the natural pentofuranose configuration are included in the chapter. Generally, syntheses of C-branched nucleosides can be grouped into two categories—namely, glycosylation of an appropriately protected nucleobase with a preconstructed C-branched carbohydrate, and direct introduction of the C branching at the pentofuranose moiety of the nucleoside. Various chemical methodologies are developed for the introduction of the C-substituent at the nucleoside level, and selected ones are discussed in the chapter. Stereoselective addition of alkyl groups to carbonyl functionalities is one of the most useful techniques in synthetic organic chemistry, and application for the synthesis of C-branched nucleosides seems to be straight-forward. Most of the syntheses discussed in the chapter involves nucleophilic addition to ketonucleosides. Numerous other types of reactions have also been applied in syntheses of C-branched nucleoside analogues, which include synthesis of 3ˊ-deoxy-3ˊ-C-methyleneuridine and -cytidine starting from uridine.