Synthesis of carbohydrate containing complex natural compounds

Many carbohydrate-containing complex natural compounds are found in nature as important biological substances [1]. A large number of recent biological studies on these glycosubstances, which possess mono- and oligosaccharides, such as proteoglycans, glycoproteins, glycolipid and antibiotics at the molecular level have shed light on the biological significance of their carbohydrate parts (glycons) in molecular recognition for the transmission of biological information. Therefore, it is now recognized that carbohydrates are at the heart of a multitude of biological events. With the stimulant biological background, the efficient synthesis of not only the carbohydrate itself but also carbohydrate-containing complex natural compounds is becoming more and more important in the field of organic chemistry and chemical biology [2]. For the efficient total or partial synthesis of mono- and oligosaccharide-containing complex natural products, there are several issues to overcome. The first one is the moment of glycosidation [3], the carbohydrate attachment, within the planned sequence so as to optimize efficiency. The second issue relates to the choice of the glycosidation method to be used with regard to the yield and the stereoselectivity. The third issue is associated with the choice of appropriate protecting groups [4]. This chapter focuses on highlights of the carbohydrate chemistry leading to the successful total synthesis of some representative natural products possessing both mono- and oligosaccharide side chains and complex noncarbohydrate components, except for glycoproteins and glycolipids. In this survey of the current advances in this area, the carbohydrate-containing complex natural compounds are arbitrarily classified into three groups: (1) O-glycoside antibiotics, (2) C-glycoside antibiotics and (3) others.