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Multivalent iminosugars have been recently explored for glycosidase inhibition. Affinity enhancements due to multivalency have been reported for specific targets, which are particularly appealing when a gain in enzyme selectivity is achieved but raise the question of the binding mode operating with this new class of inhibitors. Here we describe the development of a set of tetra- and octavalent iminosugar probes with specific topologies and an assessment of their binding affinities toward a panel of glycosidases including the Jack Bean α-mannosidase (JBaMan) and the biologically relevant class II α-mannosidases from Drosophila melanogaster belonging to glycohydrolase family 38, namely Golgi α-mannosidase Manllb (GM) and lysosomal α-mannosidase LManll (LM). Veiy different inhibitory profiles were observed for compounds with identical valencies, indicating that the spatial distribution of the iminosugars is critical to fine-tune the enzymatic inhibitory activity. Compared to the monovalent reference, the best multivalent compound showed a dramatic 800-fold improvement in the inhibitory potency for JBaMan, which is outstanding for just a tetravalent ligand. The compound was also shown to increase both the inhibitory activity and the selectivity for GM over LM. This suggests that multivalency could be an alternative strategy in developing therapeutic GM inhibitors not affecting the lysosomal mannosidases. Dynamic light scattering experiments and atomic force microscopy performed with coincubated solutions of the compounds with JBaMan shed light on the multivalent binding mode. The multivalent compounds were shown to promote the formation of JBaMan aggregates with different sizes and shapes. The dimeric nature of the JBaMan allows such intermolecular cross-linking mechanisms to occur. [ABSTRACT FROM AUTHOR]

The preparation of bicyclic carbohydrate mimics related to (+)-castanospermine incorporating a thiohydantoin moiety is reported. The synthetic approach is compatible with molecular diversity-oriented strategies and involves α-azidoesters, built at the C-5/C-6 segment in gluco- or galacto-furanose scaffolds, as the key precursors. Reduction to the corresponding α-amino ester and in situ coupling with isothiocyanates afford thioureidoester intermediates that undergo spontaneous cyclization to the corresponding hydantoins, β-elimination, and furanose → indolizidine rearrangement in a tandem manner. Biological evaluation of the new sp²-iminosugar-type glycomimetics evidenced a strong influence of the nature of the substituents at the nitrogen or oxygen atoms on the glycosidase inhibitory properties. [ABSTRACT FROM AUTHOR]

Abstract: The preparation of polyhydroxylated 6-oxa-nor-tropane glycomimetics structurally related to the glycosidase inhibitor family of the calystegines is reported. The synthetic strategy involves the furanose→piperidine rearrangement of 5-deoxy-5-ureido-l-idose precursors, followed by intramolecular glycosylation involving the primary hydroxyl group. Inversion of the configuration at C-3 in the resulting 6-oxa-(+)-calystegine B2 analogue allows accessing the elusive 3-epi-6-oxa-(+)-calystegine B2 skeleton. Acid-catalyzed opening of the nor-tropane bicycle was observed, however, which could be avoided by careful neutralization of the reaction mixture. The inhibition results suggest that (+)-calystegine B2 derivatives and the corresponding C-3 epimers can be seen as glucomimetics and galactomimetics, respectively, pointing to a 1-azasugar mode of action for this family of alkaloids. [Copyright &y& Elsevier]

Abstract: New fluorescently-labelled sp2-iminosugars based on the 5N,6S-[N′-(4-aminobutyl)iminomethylidene]-6-thionojirimycin skeleton have been synthesized as photoprobes to monitor glycosidase binding. Dansyl, dapoxyl and coumarin fluorophores were appended to the terminal amino group at the N′-substituent by either sulfonamide or amide bridging reaction. All the conjugates behaved as strong (low micromolar to nanomolar) and selective inhibitors of β-glucosidases (almonds and bovine liver) and naringinase, in agreement with the inhibition pattern previously encountered for related iso(thio)urea-type bicyclic sp2-iminosugars. The presence of the fluorescent probe allows real-time and continuous monitoring of β-glucosidase inhibition by fluorescence resonance energy transfer (FRET), taking advantage of the intrinsic tryptophan-associated fluorescence of the protein. [Copyright &y& Elsevier]