The acid hydrolysis of glycosides

Glycosidation-anomerisation reactions of 6,1-anhydroglucopyranuronic acid and anomerisation of beta-D-glucopyranosiduronic acids promoted by SnCl(4)

The reaction of silylated nucleophiles with 6,1-anhydroglucopyranuronic acid (glucuronic acid 6,1-lactones) catalysed by tin(IV) chloride provides 1,2-trans or 1,2-cis (deoxy)glycosides in a manner dependent on the donor structure. The alpha-glycoside was obtained for reactions of the donor with the 2-acyl group and 2-deoxydonors, whereas the 2-deoxy-2-iodo donor gave the beta-glycoside. Experimental evidence shows that when 1,2-cis-glycoside formation occurs, the anomerisation of initially formed 1,2-trans-glycosides catalysed by SnCl(4) is possible. The anomerisation of beta-D-glucopyranosiduronic acids was found to be faster, in some cases, than anomerisation of related beta-D-glucopyranosiduronic acid esters and beta-D-glucopyranoside derivatives and the rates are dependent on the structure of the aglycon. Moreover, the rates of anomerisation of beta-D-glucopyranuronic acid derivatives can be qualitatively correlated with rates of hydrolysis of beta-D-glucopyranosiduronic acids. Mechanistic possibilities for the reactions are considered.

The synthesis of cyclic imidates from amides of glucuronic acid and investigation of glycosidation reactions

The synthesis of novel cyclic glycosyl imidates and an investigation of their potential as donors in glycosidation reactions is described. The results show that 1,2-cis glycosides obtained from the reactions of glycosyl acetates or cyclic imidates, each derived from amides of glucuronic acid, result from the anomerisation of initially formed 1,2-trans glycosides.

Specific conversion of D-galactose into D-galacturonic acid residues in glycoproteins: a facile method for carbohydrate linkage-analysis

The terminal D-galactopyranosyl residues of asialoglycopeptides isolated from human alpha1-acid glycoprotein were oxidized in nearly quantitative yield to the corresponding uronic acid residues by a two-step sequence employing D-galactose oxidase followed by treatment with Tollens reagent, Ag(NH3)+2. Mild acid hydrolysis of the oxidized glycopeptides led to the isolation of the corresponding aldobiuronic acid(s). Structural and colorimetric analysis revealed that only one aldobiuronic acid 2-amino-2-deoxy-4-O-(beta-D-galactopyranosyluronic acid)-D-glucose, was isolated from the oxidized glycopeptides of alpha1-acid glycoprotein. This method can readily distinguish between the (1 leads to 3), (1 leads to 4), and (1 leads to 6) isomers of the corresponding aldobiuronic acids.