Synthesis of a library of allyl α-l-arabinofuranosyl-α- or β-d-xylopyranosides; route to higher oligomers

Six isomeric disaccharides allyl 2,3,5-tri-O-benzoyl-α-l-arabinofuranosyl-α-d-xylopyranosides and β-d-xylopyranosides were synthetized by the stereoselective glycosylation of pure allyl α- or β-d-xylopyranosides with 1-O-acetyl-2,3,5-tri-O-benzoyl-l-arabinofuranose as donor, catalyzed with BF3·Et2O in DCM. Regio- and stereoselective glycosylation with excess of donor furnished almost exclusively the trisaccharides allyl 2,3-di-O-(2,3,5-tri-O-benzoyl-α-l-arabinofuranosyl)-α- or β-d-xylopyranosides. Extension of the reaction to the triol β-d-xylopyranosyl-(1→4)-1,2,3-tri-O-acetyl-α-d-xylopyranose, obtained from the 4-hydroxyl penta-O-acetyl-α-xylobiose, gave in the same manner the tetrasaccharide [2,3-di-O-(2,3,5-tri-O-benzoyl-α-l-arabinofuranosyl)-β-d-xylopyranosyl]-(1→4)-1,2,3-tri-O-acetyl-α-d-xylopyranose. The protocol described herein should offer the possibility to produce branched oligosaccharides with a 2,3-di-O-(α-l–Araf)-β-d-Xylp block unit at the terminal non-reducing end.