Hydrolysis of the GlcNAc oxazoline: deamidation and acyl rearrangement.

The specific deamidation of 2-acetamido-1,3,4,6-tetra-O-acetyl-alpha-D-glucopyranose is achieved by p-toluenesulfonic acid-promoted hydrolysis of 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-alpha-D-glucopyrano)-[2,1 -d]-2- oxazoline 2 to give quantitative formation of the 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-alpha-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 alpha and beta anomers. Thus, hydrolysis of GlcNAc oxazoline 2 gives the amino-ester 5 as the kinetic product and the amido-alcohol 4 as the thermodynamic product.