Recent Developments in the Synthesis of Glycoconjugates

Abstract

The biological significance of glycoconjugates has stimulated a great synthetic activity in the synthesis of these structurally demanding compounds. These efforts were in the beginning mainly concentrated on improvements of the well-known KOENIGS-KNORR METHOD providing finally a very valuable methodology for glycoconjugate synthesis. However, due to several, mainly inherent disadvantages other anomeric oxygen exchange reactions have been investigated for the generation of glycosyl donor properties. For instance, GLYCO- SYL FLUORIDES and SULFIDES and their activation with fluorophilic and thiophilic catalysts, respectively, was studied in several laboratories, as shortly discussed. Other activation principles were investigated in our laboratory, namely the base catalyzed activation retaining the anomeric oxygen atom. This led to the direct ANOMERIC O- ALKYLATION procedure with primary triflates as the alkylating agents providing a most convenient method for glycoside bond formation due to its simplicity and the yields and stereoselectivities obtained. However, the direct base catalyzed activation with trichloroacetonitrile afforded O-glycosyl- trichloroacetimidates which are in terms of stability, reactivity, and general applicability outstanding glycosyl donors. The scope of this TRICHLOROACETIMIDATE METHOD is summarized in this paper. © 1989 IUPAC.