The synthesis of imidazol sugars which mimic cyclic carboxonium ions formed during the glycosidase-catalysed hydrolysis of oligo- and polysaccharides

Some naturally occurring carbohydrates, of which several hydroxy groups had been selectively protected, were condensed with formamidine to give the ex pected imidazole derivatives in the D-arabino (9), D-lyxo (12), L-xylo (17) , D-threo (21), and in the L- and D-erythro (24) series. Introduction of a strong leaving group at the remaining free alcohol function of these produc ts led at once to intramolecular S(N)2 cyclisation to the corresponding bic yclic aza sugar derivatives. This was followed by total deprotection to giv e the target aza sugars in the L-xylo (7), L-ribo (14), D-arabino (19), as well as in the D-threo (22) and the L- and D-erythro (26) series. Inhibitor y assays with four glycosidases showed that the D-arabino aza sugar 19 is t he only potent inhibitor (for an alpha-mannosidase of jack bean).