Glycosidase inhibitors of gem-diamine 1-N-iminosugars structures in media of enzyme assays

Molecular Basis for Inhibition of Heparanases and β-Glucuronidases by Siastatin B

Siastatin B is a potent and effective iminosugar inhibitor of three diverse glycosidase classes, namely, sialidases, β-d-glucuronidases, and N-acetyl-glucosaminidases. The mode of inhibition of glucuronidases, in contrast to sialidases, has long been enigmatic as siastatin B appears too bulky and incorrectly substituted to be accommodated within a β-d-glucuronidase active site pocket. Herein, we show through crystallographic analysis of protein-inhibitor complexes that siastatin B generates both a hemiaminal and a 3-geminal diol iminosugar (3-GDI) that are, rather than the parent compound, directly responsible for enzyme inhibition. The hemiaminal product is the first observation of a natural product that belongs to the noeuromycin class of inhibitors. Additionally, the 3-GDI represents a new and potent class of the iminosugar glycosidase inhibitor. To substantiate our findings, we synthesized both the gluco- and galacto-configured 3-GDIs and characterized their binding both structurally and kinetically to exo-β-d-glucuronidases and the anticancer target human heparanase. This revealed submicromolar inhibition of exo-β-d-glucuronidases and an unprecedented binding mode by this new class of inhibitor. Our results reveal the mechanism by which siastatin B acts as a broad-spectrum glycosidase inhibitor, identify a new class of glycosidase inhibitor, and suggest new functionalities that can be incorporated into future generations of glycosidase inhibitors.

Contributing to the Study of Enzymatic and Chemical Glycosyl Transfer Through the Observation and Mimicry of Glycosyl Cations

This account describes our efforts dedicated to: 1) the design of glycomimetics aimed at targeting therapeutically relevant carbohydrate processing enzymes, and 2) the observation, characterization, and exploitation of glycosyl cations as a tool for studying the glycosylation reaction. These findings have brought important data regarding this key ionic species as well as innovative strategies to access iminosugars of interest.

1 Introduction

2 The Glycosyl Cation, A Central Species in Glycosciences

2.1 A Selection of the Strategies Developed so far to Gain Insights into Glycosyl Cations Structure

2.2 When Superacids Meet Carbohydrates

3 Chemical Probes to Gain Insights into the Pseudorotational Itinerary of Glycosides During Glycosidic Bond Hydrolysis

3.1 Conformationally Locked Glycosides

3.1.1 The Xylopyranose Case

3.1.2 The Mannopyranose Case

3.2 Conformationally Flexible Iminosugars

3.2.1 Nojirimycin Ring Homologues

3.2.2 Noeuromycin Ring Homologues

3.2.3 Seven-Membered Iminosugar C-Glycosides

4 N-Acetyl-d-glucosamine Mimics

5 Ring Contraction: A Useful Tool to Increase Iminosugar’s Structural Diversity

6 Regioselective Deprotection of Iminosugar C-Glycosides to Introduce Diversity at C2 Position

7 Conclusion

Stable analogues of nojirimycin – synthesis and biological evaluation of nojiristegine and manno-nojiristegine

Two novel iminosugars called nojiristegines, being structural hybrids between nor-tropane alkaloid calystegine and nojirimycins, have been synthesised and the hemiaminal functionality found to be stable.

Synthesis and glycosidase inhibitory activity of noeurostegine-a new and potent inhibitor of beta-glucoside hydrolases

A new, stable hemi-aminal nor-tropane christened noeurostegine was synthesised in 22 steps from levoglucosan and tested for inhibitory activity against glycoside hydrolases. Sweet almond and Thermotoga maritimabeta-glucosidases, coffee bean alpha-galactosidase, and Asp. oryzaebeta-galactosidase were inhibited in the low micromolar region but significant tightening of binding to K(i) 50 nM for almond beta-glucosidase was found to occur after pre-incubation. Yeast alpha-glucosidase and E. colibeta-galactosidase were not inhibited at 1 mM.

Glycosidase mechanisms

The three-dimensional structure of glycosidases and of their complexes and the study of transition-state mimics reveal structural details that correlate with mechanism. Of particular interest are the transition-state conformations harnessed by individual enzymes and the substrate distortion observed in enzyme-ligand complexes. 3D-structure in synergy with transition-state mimicry opens the way for mechanistic interpretation of enzyme inhibition and for the development of therapeutic agents.