Design, Synthesis, and Biological Evaluation of Enantiomeric β‐N‐Acetylhexosaminidase Inhibitors LABNAc and DABNAc as Potential Agents against Tay‐Sachs and Sandhoff Disease

Abstract

N-Acetylhexosaminidases are of considerable importance in mammals and are involved in various significant biological processes. In humans, deficiencies of these enzymes in the lysosome, resulting from inherited genetic defects, cause the glycolipid storage disorders Tay-Sachs and Sandhoff diseases. One promising therapy for these diseases involves the use of beta-N-acetylhexosaminidase inhibitors as chemical chaperones to enhance the enzyme activity above sub-critical levels. Herein we describe the synthesis and biological evaluation of a potent inhibitor, 2-acetamido-1,4-imino-1,2,4-trideoxy-L-arabinitol (LABNAc), in a high-yielding 11-step procedure from D-lyxonolactone. The N-benzyl and N-butyl analogues were also prepared and found to be potent inhibitors. The enantiomers DABNAc and NBn-DABNAc were synthesised from L-lyxonolactone, and were also evaluated. The L-iminosugar LABNAc and its derivatives were found to be potent noncompetitive inhibitors of some beta-N-acetylhexosaminidases, while the D-iminosugar DABNAc and its derivatives were found to be weaker competitive inhibitors. These results support previous work postulating that D-iminosugar mimics inhibit D-glycohydrolases competitively, and that their corresponding L-enantiomers show noncompetitive inhibition of these enzymes. Molecular modelling studies confirm that the spatial organisation in enantiomeric inhibitors leads to a different overlay with the monosaccharide substrate. Initial cell-based studies suggest that NBn-LABNAc can act as a chemical chaperone to enhance the deficient enzyme's activity to levels that may cause a positive pharmacological effect. LABNAc, NBn-LABNAc, and NBu-LABNAc are potent and selective inhibitors of beta-N-acetylhexosaminidase and may be useful as therapeutic agents for treating adult Tay-Sachs and Sandhoff diseases.

Lysosomal storage of oligosaccharide and glycosphingolipid in imino sugar treated cells

“…In murine RAW264.7 macrophage-like cell extracts, this compound inhibited β-hexosaminidase activity at low micromolar concentrations (Table 1) in a predominantly noncompetitive manner using artificial substrates, as determined by Lineweaver-Burk plots (data not shown), consistent with the inhibition of other mammalian and plant-derived hexosaminidases [20]. SR1 also differentially enhances the activity of mutant β-hexosaminidase A and B in cells derived from a Tay-Sachs patient, indicative of an additional, chemical chaperone property at non-inhibitory concentrations [20].…”

Iminosugars: The Potential of Carbohydrate Analogs

“…Swainsonine is a powerful inhibitor of lysosomal [46] and Golgi α-mannosidase II [47], while lentiginosine is a reasonably good inhibitor of fungal amyloglucosidase, with an inhibitory constant (K i ) value of 10 μM, but it does not inhibit other α-glucosidases, or any other glycosidases [44]. In 1995, on the basis of the synthesis of both (+)-lentiginosine (13) and (-)-lentiginosine (14) and their inhibition of amyloglucosidase, the natural alkaloid was assigned as (+)-lentiginosine [48]. Synthetic (+)-lentiginosine displayed amyloglucosidase inhibition (K i = 2 μM) five times stronger than that reported for natural lentiginosine, and 35 times stronger than that measured for (-)-lentiginosine [48].…”

“…This may be the reason why synthetic l-iminosugars have attracted little attention. However, in recent years, Fleet et al have published amazing reports stating that some synthetic five-membered l-iminosugars are much more potent inhibitors of d-glycosidases than their d-enantiomers, and further show improved selectivity in d-glycosidase inhibition [11][12][13][14]. Thus, the importance for l-iminosugars is being rapidly reconsidered [15].…”

Development of targeted therapies for Parkinson's disease and related synucleinopathies

“…In cell-based studies, NBn-LABNAc was shown to act as a chaperone and restore defi cient enzyme activity ( 79 ). To date, little information is available on whether these can function as chaperones in vivo.…”