BASIC SUGAR DERIVATIVES, TOOLS FOR MAPPING THE ACTIVE SITE OF GLYCOSIDASES AND FOR THE STUDY OF GLYCOPROTEIN BIOSYNTHESIS

Abstract

Most glycoside hydrolases are strongly inhibited by sugar derivatives with a basic nitrogen adjacent to their C-1. This is assumed to be due to the formation of an ion pair at the catalytic site consisting of the protonated inhibitor and a negatively charged group essential for catalysis. While glycosylamines and their N-alkylderivatives are useful for kinetic studies to characterize the active site with respect to charge distribution, hydrophobic properties and solvent accessibility,their life-time in aqueous solution is too short for long term studies. Stable sugar derivatives with suitable properties are 5-amino-5-deoxyhexopyranoses and 1,5-dideoxy-1,5-imino hexitols. The basic principle of their synthesis is the oxidation of a protected furanoid monosaccharide at C-5 and conversion of the resulting ketone to the epimeric amines by reduction of its oxime. Deprotection provides the pyranoid sugar derivative with the basic nitrogen in the ring. In glycoprotein biochemistry these inhibitors have been used to specifically inhibit the 'trimming' glycosidases that catalyze essential steps in the conversion of the primary asparagine linked Gle Man (GlcNAc) unit to complex type or high mannose type glycans. Interference with these steps is expected to provide insight into the role of glycan structure in surface expression, secretion and receptor binding. Another application is the construction of affinity ligands for the purification of these enzymes.