Kinetic studies on the acid hydrolysis of the methyl ketoside of unsubstituted and O-acetylated N-acetylneuraminic acid.

The hydrolysis of the model compound 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl-alpha-d-neuraminic acid and neuraminidase (Vibrio cholerae) closely resembled that of the O-acetylated sialic acid residues of rabbit Tamm-Horsfall glycoprotein. This confirmed that O-acetylation was responsible for the unusually slow rate of acid hydrolysis of O-acetylated sialic acid residues observed in rabbit Tamm-Horsfall glycoprotein and their resistance to hydrolysis by neuraminidase. The first-order rate constant of hydrolysis of 2-methyl-N-acetyl-alpha-d-neuraminic acid by 0.05m-H(2)SO(4) was 56-fold greater than that of 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl -alpha-d-neuraminic acid. Kinetic studies have shown that in the pH range 1.00-3.30, the observed rate of hydrolysis of 2-methyl-N-acetyl-alpha-d-neuraminic acid can be attributed to acid-catalysed hydrolysis of the negatively charged CO(2) (-) form of the methyl ketoside.