"One-pot" synthesis of 2-acetamido-2-deoxy-1,3,6-tri-O-acetyl-α-D-glucopyranose as intermediate for N-acetyl-α-D-lactosamine heptaacetate preparation

We have recently reported the synthesis of different acyl pyranoses, bearing only one free hydroxyl group, obtained by regioselective enzymatic hydrolysis of the peracetylated precursors and subsequent acyl migration of the hydrolyzed products. As a part of this ongoing research, we have focused our attention onto the pure regioisomers of 2-acetamido-2-deoxy-1,3,4,6-tetra- O-acetyl-α-D-glucopyranose (1) as key intermediate for the preparation of a large number of oligosaccharides. Particularly, we have developed an efficient process to obtain a deprotected derivative of 1 having only one free hydroxyl group at the C-4 position (3) as a valuable synthon for the preparation of N-acetyl-α-D-lactosamine heptaacetate (4), building-block in a new synthetic pathway for oligosaccharides like Sialyl Lewis x. Our chemo-enzymatic strategy allows to obtain the disaccharide (4) in good overall yield, starting from a commercially available cheap compound and without any intermediate purification. Our approach is, indeed, an interesting alternative to the classical multi-step chemical procedures that are often plagued by low yields and formation of undesired by-products.