α-Secondary Tritium Isotope Effects in the Hydrolysis of Glycopyranosides of N-Acetyl-D-Glucosamine

Author: Mohr, Lawrence Henry

Year: 1974

Degree: Master's thesis

Advisor: Raftery, Michael A.

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/6EZB-BP10

Abstract

Part I. Secondary tritium isotope effects were used to study the aqueous hydrolysis of a series of α and β-glycopyranosides of N-acetyl-D-glucosamine. The magnitude of the secondary tritium isotope effects, and their dependence on the structure of the aglycone, are compatible with the carbonium ion mechanism suggested for the specific acid catalysis of these compounds by Piszkiewicz and Bruice (1, 2, 3). The secondary tritium isotope effect determined for the spontaneous hydrolysis of the p-nitropheny1-2-acetamido-2-deoxy-β-D-glucopyrano- side is not consistent with an intramolecular, nucleophilic displacement mechanism. A mechanism involving the equilibrium formation of a carbonium ion-anion pair is proposed. The relevance of these model studies to hydrolysis of oligosaccharides of N-acetyl-D-glucosamine by lysozyme is discussed.

Part II. Secondary tritium isotope effects are also used to study the enzymatic hydrolysis of two β-aryl glycopyranosides of N-acetyl-D-glucosamine by β-N-acetyl-D-glucosaminidase isolated from jack bean meal. The results obtained indicate a transition state for reaction processing less carbonium ion character than the corresponding hydrolysis catalyzed by aqueous acid or lysozyme. A mechanism involving anchimeric assistance by the acetamido group on the substrate is proposed.

Files