An original chemoenzymatic route for the synthesis of β-d-galactofuranosides using an α-l-arabinofuranosidase Original Research Article

Galactofuranose is a widespread component of cell wall polysaccharides in bacteria, protozoa and fungi, but is totally absent in mammals. Importantly, galactofuranose is a key constituent of major cell envelope polysaccharides in pathogenic mycobacteria. In this respect, galactofuranose-based glycoconjugates are interesting target molecules for drug design. O-Glycosidases and notably β-d-galactofuranosidases could be useful tools for the chemoenzymatic synthesis of galactofuranosides, but to date no studies of this type have been reported. Here we report the use of a GH 51 α-l-arabinofuranosidase for the synthesis of β-d-galactofuranosides. We have demonstrated that this enzyme can catalyse both the autocondensation of p-nitrophenyl-β-d-galactofuranoside and the transgalactofuranosylation of benzyl α-d-xylopyranoside, forming p-nitrophenyl β-d-galactofuranosyl-(1→2)-β-d-galactofuranoside and benzyl β-d-galactofuranosyl-(1→2)-α-d-xylopyranoside, respectively. Both reactions were very regiospecific and the reaction involving benzyl α-d-xylopyranoside afforded very high yields (74.8%) of the major product. To our knowledge, this demonstration of chemoenzymatic synthesis of galactofuranosides constitutes the very first use of an O-glycosidase for the synthesis of galactofuranosides.