The Multivalent Effect in Glycosidase Inhibition: Probing the Influence of Valency, Peripheral Ligand Structure, and Topology with Cyclodextrin‐Based Iminosugar Click Clusters

Abstract

In view of recent reports of a strong multivalent effect in glycosidase inhibition, a library of β-CD-based multivalent iminosugars has been efficiently synthesized by way of Cu(I) -catalyzed azide-alkyne cycloaddition (CuAAC). In combination with the first application of isothermal titration calorimetry (ITC) experiments to the study of multivalent iminosugar-enzyme interactions, the inhibition properties of these click clusters were evaluated on a panel of glycosidases. The structural parameters that were varied include valency, peripheral ligand structure, and topology. The inhibition results obtained with the iminosugar clusters further highlight the importance of multivalency in the inhibition of α-mannosidase. Generally, the evaluated multivalent iminosugars displayed comparable thermodynamic signatures of binding towards α-mannosidase (Jack bean): that is, large negative enthalpies of complexation coupled with small entropies of either sign. In addition, the enthalpy-entropy compensation observed in all tested cases may be attributed to a common mechanism of dissociation for the enzyme-multivalent iminosugar interactions. The measured binding stoichiometries indicated that each iminosugar cluster interacts with no more than one protein molecule.

Synthesis of the first examples of iminosugar clusters based on cyclopeptoid cores

“…N -alkyl derivatives of DNJ were logically chosen as the peripheral ligands because of the therapeutic relevance of these compounds [42]. In addition, most of the glycosidase inhibitor clusters published in the literature are based on these binding motifs [1–7 11,43] providing thus the opportunity to assess the relevance of cyclopeptoid cores by comparison with the other platforms already described.…”

“…The last stages of the DNJ cluster synthesis were based on a robust two-step process, recently developed in our group for the preparation of iminosugar click clusters [4–5 9–11]. The first step of the process involved the attachment of peracetylated azido iminosugars 5 [4] onto polyalkyne scaffolds 2 – 4 by microwave-assisted CuAAC reaction (Scheme 2).…”

“…As indicated in the introduction, the best multivalent effects in glycosidase inhibition observed so far were obtained with jack bean α-mannosidase [1–7 11–12]. Accordingly, in order to complete these compelling investigations, evaluation of the inhibition potency of multivalent iminosugars 10 was performed on this peculiar enzyme (Table 1).…”

“…The mechanisms underlying the inhibitory multivalent effect were studied with different methods such as isothermal titration calorimetry, competitive lectin-enzyme assays, X-ray crystallography or atomic force spectroscopy [7,11–13]. At this stage of research, one of the main challenges in the field is to design optimal systems that not only display large multivalent effects but also possess the desired properties for particular applications.…”

Multimeric xanthates as carbonic anhydrase inhibitors

“…The term ''multivalent effect'', generally only employed with carbohydrate-binding proteins, could then be applied to the field of carbohydrate-processing enzymes. After this groundbreaking result, considerable amount of research has been reported, although almost exclusively with carbohydrate-processing enzymes such as glycosidases [34][35][36][37][38][39][40][41][42] and glycosyltranferases 43 . In a recent work, we reported the inhibitory study of coumarinderivatized fullerene hexakis-adducts toward a set of biologically relevant hCA isoforms 44 .…”