Recent Trends in Regioselective Protection and Deprotection of Monosaccharides

Carbohydrates are complex and structurally diverse compounds in nature with key roles in a broad range of life processes, including signal transduction, carcinogenesis and immune responses. Many natural products contain oligosaccharides that are vital for their biological activity. However, the synthesis of complex oligosaccharides and other glycoconjugates is hampered by difficulties associated with the regioselective protection of polyhydroxyls and challenges related to the stereoselective assembly of glycosidic linkages. Therefore, a big challenge in glycochemistry is to have selectively protected monosaccharide units, one with a strategically positioned free hydroxy group (a nucleophilic acceptor for further glycosylation or functional-group modifications) and suitable protecting groups on the remaining hydroxyls. The present review discusses some of the most recent advances in the synthesis of these building blocks by regioselective protection or deprotection procedures. These strategies have permitted to achieve hundreds of different building blocks, with a good potential in a combinatorial approach synthesis of complex glycoconjugates. Special focus will be positioned on the new advances in biocatalysis in these reactions.