Predominantly found as the outermost carbohydrate units on glycoproteins and glycolipids of vertebrates, sialic acids play vital roles in a variety of physiological and pathological processes. The ability of obtaining homogeneous sialosides, especially those containing various modifications on sialic acids, is of great interest for studies on the mechanism and significance of sialic acid structural diversity.;This thesis presents a practical and efficient approach to the synthesis of important sialosides containing various KDN modifications, which are useful compounds for testing biological functions of sialoside derivatives. The research consists of two main sections: (1) chemical synthesis of mannose derivatives, and (2) enzymatic synthesis of sialosides containing KDN and its derivatives using synthetic mannose derivatives as sialic acid precursors.;Seven mannose derivatives with a fluoro-, methyl-, or azido-functional group on different positions of the mannose backbone, have been chemically synthesized. These compounds have been employed to investigate the substrate specificities of sialoside' biosynthetic enzymes. A library of sialosides containing various KDN modifications has been obtained utilizing recent progress in efficient chemo-enzymatic synthesis of functionalized sialosides in a one-pot, three-enzyme developed in our laboratory.
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