A short and economical synthesis of orthogonally protected C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivatives.

A short and high-yielding synthesis has been devised to prepare C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivative 3. One of the main advantages of this approach is that it employs commercially available and inexpensive d-glucosamine as the starting material. The key steps include a highly stereoselective C-allylation followed by epimerization of the C-4 hydroxyl group. Building block 3 and orthogonally protected C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivative 2 were obtained in 44% overall yield (six steps) and 29% overall yield (eight steps), respectively. This represents a significant improvement over previously reported syntheses.