Hydrolysis of (2-deoxy-α-D-glucopyranosyl)pyridinium salts:: The 2-deoxyglucosyl oxocarbenium is not solvent-equilibrated in water

The hydrolysis reactions of four 2-deoxy-alpha-D-glucopyranosyl pyridinium salts exhibit first-order rate constants that are independent of pH in the range of 4.4-10.5 pH units. Derived second-order rate constants for the hydrolysis reactions of 2-deoxy-alpha-D-glucopyranosyl 4'-bromoisoquinolinium tetrafluoroborate (4d) conducted in the presence of nucleophilic monoanions (mu = 2.0) including AcO-, Cl-, Br-, and N-3(-) exhibit a Swain-Scott parameter (s) of 0.03 +/- 0.10, indicating that these reactions show no sensitivity to the nature of the anion. In the presence of azide ion, a substantial quantity of the 2-deoxy-alpha-glucopyranosyl 4'-bromoisoquinolinium salt hydrolysis product results from a post rate-limiting reaction of a cationic intermediate with azide. Analysis of the hydrolysis product ratios indicates that the 2-deoxyglucosyl oxocarbenium ion is not solvent-equilibrated in water. Furthermore, the reaction of solvent occurs about 2-fold faster with the cationic intermediate that is formed during solvolysis of the beta-anomeric salt than with the corresponding intermediate produced from the reactions of the alpha-anomer 4d.