Acid-Catalyzed Transformation of Pyranosides into Furanosides as a Tool for Preparation of Furanoside Synthetic Blocks

The importance of natural glycoconjugates containing furanoside residues causes a continued demand for the development of efficient methods for the synthesis of corresponding oligosaccharide derivatives to be used as molecular probes in glycobiological studies. Currently, the chemical synthesis of furanose-containing oligosaccharides often represents a significant challenge because of the lack of short, efficient, and reliable methods for the preparation of selectively substituted furanoside blocks. Herein, we report an easy protocol toward galactofuranose-containing molecules based on the unusual equilibrium between pyranoside and furanoside forms observed for a series of substituted galactosides. The method's utility is illustrated by the syntheses of furanoside-containing oligosaccharides related to the antigenic polysaccharides of <i>Aspergillus fumigatus</i> and <i>Klebsiella pneumoniae</i> O2ac.