A new stereocontrolled access to beta-D-mannopyranosides and 2-acetamido-2-deoxy-beta-D-mannopyranosides starting from beta-D-galactopyranosides

A new stereocontrolled synthesis of BETA-D-mannopyranosides was defined relying on a high yielding sequence based on the following three key steps: (a) a stereospecific inversion at C-2 of beta-D-galactopyranosides by an oxidation–reduction procedure; (b) a regiocontrolled formation of 4-deoxy-alfa-D-threo-hex-3-enopyranosides; (c) a regio- and stereocontrolled hydroboration–oxidation of the above enol ethers. The flexibility of this new method was demonstrated by its extension to the synthesis of 2-acetamido-2-deoxy-beta-D-mannopyranosides and of an orthogonally protected beta-D-mannopyranoside scaffold and, finally, by the transformation of lactose into the two biologically relevant disaccharides with primary structure BETA-D-Manp-(1->4)-D-Glc and beta-D-ManNAcp-(1->4)-D-Glc.