Fluorinated Carbohydrates. Some New Aspects in Synthesis and Application

Abstract

Abstract: Recent applications of glycosyl fluorides as donors in controlled di- and oligosaccharide synthesis employing chemical and enzymatic methods are presented. Within the chemical approaches significant contributions have been made by the development of fluorophilic activators displaying high stereoselectivity as well as further improvements in "reactivity fine tuning" by variation of protecting groups. In the field of enzymatic oligosaccharide synthesis progress has been made in regioselective glycosyl transfer to secondary hydroxyl groups. Additionally, promising new approaches employing fluorides derived from monosaccharides with specifically mutated glycosidases or disaccharide derived fluorides with cellulases, have been developed. From the numerous contributions regarding the synthesis of deoxy-fluoro aldoses, emphasis is placed upon side-reactions on attempted nucleophilic substitutions. Within this field modification of pentoses at C-2 using the sulfonate/fluoride route or applying diethylaminosulfur trifluoride are discussed. The increasing use of asymmetric synthesis in this field, including a new entry starting from a chiral cis-diol, is noteworthy. Scope and limitations in the synthesis of 2-deoxy-2-fluoro aldoses by electrophilic addition across the double bond of glycals by making use of the new class of N-F-fluorinating agents are presented. The important role of fluorinated carbohydrates as probes in mechanistic enzyme studies as well as their application in biomedical research is illustrated by several examples.