Stereocontrolled 1,2-cis glycosylation as the driving force of progress in synthetic carbohydrate chemistry

Carbohydrates, as polysaccharides or glycoconjugates, represent the largest class of naturally occurring compounds that are oen found as essential components of many bioactive molecules in nature. Carbohydrates were initially viewed as energystorage materials, structural components, and primary metabolites. Now it is known that carbohydrates mediate many fundamental biological processes such as immune defense, fertilization, metastasis, signal transduction, cell growth and cell–cell adhesion. In the past few years, we have been learning that carbohydrates play crucial roles in pathogenesis of diabetes, bacterial and viral infections, inammation, development and growth of cancers, septicemia, and many other diseases. Clearly, uncovering the contributions of carbohydrates to cell biology would greatly facilitate advances in the eld of glycosciences. For the most part, medicinally important carbohydrates exist as complex oligomers or as conjugates with other biomolecules including natural products, lipids, peptides, proteins, etc. The carbohydrate part itself exists in various sizes and shapes ranging from monomeric sugars and simple linear chains to highly branched glycoforms. Major obstacles in studying natural carbohydrates are the difficulties in isolating, characterizing, and synthesizing these molecules due to their low abundance and heterogeneity in nature. While scientists have been able to successfully isolate and characterize certain classes of natural carbohydrates, the availability of pure isolates is still low. As a consequence, the systematic study of these molecules oen relies on synthetic chemistry to provide pure compounds in signicant quantities. Among the variety of glycosidic bonds in nature, it is the O-glycosidic bonds that are of major interest and challenge to chemists due to their high abundance and difficulty in synthesis. There are two major types of O-glycosides, which are,