Hydrolysis of the GlcNAc oxazoline: deamidation and acyl rearrangement

The specific deamidation of 2-acetamido-1,3,4,6-tetra-O-acetyl-α-d-glucopyranose is achieved by p-toluenesulfonic acid-promoted hydrolysis of 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-glucopyrano)-[2,1-d]-2-oxazoline2 to give quantitative formation of the 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-α-d-glucopyranose p-toluenesulfonate (5d). This two-step procedure provides an amino sugar which may be readily acylated to give novel glycoconjugates. Alternatively, base-catalyzed O-1 → N-2 acyl rearrangement of the amino tosylate 5d gives the 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-d-glucopyranose 4 as a 9:1 mixture of α and β anomers. Thus, hydrolysis of GlcNAc oxazoline 2 gives the amino-ester 5 as the kinetic product and the amino-alcohol 4 as the thermodynamic product.