Molecular requirements of imino sugars for the selective control of N-linked glycosylation and glycosphingolipid biosynthesis

N-Butyl-deoxynojirimycin (NB-DNJ) has been approved for clinical trials as a potential therapy for Gaucher disease, a glycolipid lysosomal storage disorder. As this compound has both glycoprotein processing alpha-glucosidase and ceramide glucosyltransferase inhibitory activity, we have sought to determine the molecular basis for these two activities. NB-DNJ is known to resemble the positively charged oxocarbonium-like transition state for alpha-glucosidase I and the structure-function relationships we present now help to define the recognition epitope for the enzyme. Inhibition of ceramide glucosyltransferase by NB-DNJ was competitive for ceramide (K-i=7.4 mu M) and non-competitive for UDP-glucose, indicating inhibitory activity is by ceramide mimicry. The presence of an N-alkyl chain was obligatory for transferase inhibition and increases in alkyl chain length provided a modest increase in inhibitory potency. By contrast, alpha-glucosidase inhibition was independent of the N-alkyl chain and changes in chain length. The effects of ring substitutions identified the C-3 hydroxyl group as being critical for both enzymes but C-1 and C-6 modifications led to a loss of transferase inhibition only. Attempts to rationalise these data for transferase inhibition using an energy minimised molecular model of NB-DNJ and ceramide predicted structural homology of three stereogenic centres and the N-alkyl chain of NB-DNJ, with the trans-alkenyl and N-acyl chain of ceramide. On the basis of these studies, modifications to imino sugar inhibitors can be suggested that allow a more selective approach for molecular inhibition of both ceramide glucosyltransferase and alpha-glucosidase I, leading to improved compounds for the potential treatment of lysosomal glycosphingolipid storage disorders and viral infections, respectively (C) 2000 Published by Elsevier Science Ltd. All rights reserved.