Synthesis of N4-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine analogues: succinamide, L-2-hydroxysuccinamide, and L-2-hydroxysuccinamic acid hydrazide analogues

Glycosylasparaginase activity requires the alpha-carboxyl group, but not the alpha-amino group, on N(4)-(2-Acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine

Glycosylasparaginase catalyzes the hydrolysis of the N-glycosylic bond in N(4)-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine in the catabolism of N-linked oligosaccharides. A deficiency, or absence, of enzyme activity gives rise to aspartylglycosaminuria, the most common disorder of glycoprotein metabolism. The enzyme catalyzes the hydrolysis of a variety of asparagine and aspartyl compounds containing a free alpha-carboxyl group and a free alpha-amino group; computational studies suggest that the alpha-amino group actively participates in the catalytic mechanism. In order to study the importance of the alpha-carboxyl group and the alpha-amino group on the natural substrate to the reaction catalyzed by the enzyme, 14 analogues of the natural substrate were studied where the structure of the aspartyl group of the substrate was changed. The incremental binding energy (DeltaDeltaGb) for those analogues that were substrates was calculated. The results show that the alpha-amino group may be substituted with a group of comparable size, for the alpha-amino group contributes little, if any, to the transition state binding energy of the natural substrate. The alpha-amino group position acts as an "anchor" in the binding site for the substrate. On the other hand, the alpha-carboxyl group is necessary for enzyme activity; removal of the alpha-carboxyl group or changing it to an alpha-carboxamide group results in no hydrolysis reaction. Also, N-acetyl-D-glucosamine is not sufficient for binding to the active site for efficient hydrolysis by the enzyme. These results provide supporting evidence for a proposed intramolecular autoproteolytic activation reaction for the enzyme. However, the results raise a question as to an important role for the alpha-amino group in the catalytic mechanism as indicated in computational studies.

Synthesis of N4-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine analogues. n-Butyramide, 3-chloropropionamide, 3-aminopropionamide, and isovaleramide analogues

The syntheses of four analogues of N4-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-L-asparagine are described. Activated carboxylic acids were reacted with 2-acetamido-2-deoxy-beta-D-glucopyranosylamine. n-Butyric anhydride gave N-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-n-butyramide. 3-Chloropropionic anhydride was synthesized from 3-chloropropionic acid and gave N-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-3-chloropropionamide. Equilibration of the latter with ammonium bicarbonate gave N1-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-3-aminopropionamide. Succinimidyl isovalerate was synthesized and gave N-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-isovaleramide.