| Carbohydrates, which constitute one of the most abundant types of biomolecules, are not only involved in almost every aspect of biology, but also central to many processes that are at the core of important diseases. Combined with proteins or lipids on cell surface, carbohydrates, especially oligosaccharides, perform a much broader role in biological science, especially in physiological and pathological processes, molecular recognition, signal transduction, cell communication, cell differentiation and developmental events. Therefore, oligosaccharides have been widely recognized as potential Pharmaceuticals for the prevention of infection, the neutralization of toxin and the immunotherapy of cancer. And the sugar moieties of the Pharmaceuticals have been proven to dictate the biological activity, pharmaceutical kinetics and drug potency. Therefore, further growth in research on the biological functions of the varied carbohydrate structures will undoubtedly be closely tied to the availability of bioactive carbohydrates. .However, the application of oligosaccharides in modern medicine is limited by the inability to produce sufficient quantities of the required carbohydrate moiety. In contrast to the in-depth understanding of protein and nucleic acid biosynthesis and mature technology available for routine in vitro synthesis, the progresses towards understanding the biosynthesis of complex carbohydrate molecules and the development of practical in vitro synthetic route are very limited. The major difficulty lies in the enormous variations of carbohydrate structures reflecting in the diverse glycosidic linkage patterns, stereochemistry and branching. In addition, compared with the biosynthesis of DNA and proteins whose primary structure are encoded by a piece of template sequence, carbohydrate biosynthesis requires coordination of various enzymes which are encoded by separate genetic loci. Technical difficulty in synthesizing practical...
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