Philippe Compain

Carbohydrate mimetics-based glycosyltransferase inhibitors

The search for carbohydrate mimetics-based glycosyltransferase inhibitors is a dynamic field that emerged 10 years ago. This review presents a description of the different types of glycosyltransferase inhibitors containing a carbohydrate mimetic (primarily an iminosugar, a carbasugar or a C-glycoside) and data on their biological activity whenever such data are available. The purpose of this account is to foster a synergy between the two expanding research areas of glycomimetics and glycosyltransferases.

Design, Synthesis and Biological Evaluation of Iminosugar-Based Glycosyltransferase Inhibitors

Due to their pivotal role in the biosynthesis of oligosaccharides and glycoconjugates, glycosyltransferases represent targets of choice for the development of potent inhibitors and therefore for drug discovery. Since glycosyltransferase reactions are thought to proceed through transition states similar to those of glycosidases, iminosugars and the related compounds have been recently used to design potential inhibitors of this major class of enzymes. The purpose of this review is to stimulate further research in this promising area by providing a description and a biological evaluation of the different types of inhibitors containing an iminosugar. These data in addition to the recent insights into the structural basis of glycosyltransferase catalysis may constitute the first steps toward a rational design of potent glycosyltransferases inhibitors.

Glycosidase Inhibition with Fullerene Iminosugar Balls: A Dramatic Multivalent Effect†

The electronic and structural properties of fullerene derivatives make them very attractive candidates for the construction of nanostructures that are potentially useful for applications in materials science and biological chemistry. In particular, the C60 hexakis adducts with a Th-symmetrical octahedral addition pattern initially developed by Hirsch and co-workers are unique organic molecules with an appealing compact spherical scaffold for the construction of multifunctional nanomaterials. However, the synthesis of functionalized fullerene hexakis adducts from malonates and C60 is difficult. 4] This major problem limits the applications of such systems and has been recently solved by the development of synthetic methodologies based on the postfunctionalization of easily accessible building blocks of fullerene hexakis adducts. 6] It has been shown that fullerene hexakis adducts that bear 12 peripheral carbohydrate moieties can be prepared in excellent yields by grafting unprotected sugar derivatives onto the fullerene core. Although these fullerene sugar balls are obviously perfectly suited for applications in the field of carbohydrate–lectin interactions, the evaluation of carbohydrate-processing enzyme inhibition with such multivalent derivatives is less obvious. Indeed, among the possible strategies to attain specific potent glycosidase inhibition, the concept of multivalent design has been clearly overlooked. Most enzymes actually have a single, deep active site that is usually less accessible than the shallow binding pockets or grooves on the lectin surfaces. Consequently, a limited number of binding mechanisms, including statistical rebinding, are possible, whereas multivalent ligands may interact with multiple receptors by additional mechanistic options (e.g., the chelate effect, receptor clustering). It is likely that these factors may have hampered interest in projects directed towards the design of multivalent glycosidase inhibitors. In addition, the experimental results obtained to date were not particularly encouraging. Dito tetravalent analogues of 1-deoxynojirimycin, which is a well-known glycosidase inhibitor, generally displayed comparable if not decreased inhibition compared with their monomeric counterparts. The best result reported to date was found for a trivalent iminosugar that showed a sixfold affinity enhancement towards Jack bean a-mannosidase. Herein we report the synthesis of a fullerene hexakis adduct decorated with 12 iminosugar residues. The inhibition profile of this fullerene iminosugar ball has been systematically evaluated against various glycosidases, and dramatic multivalent effects have been observed for the first time. In order to explore the potential of multivalency on glycosidase inhibition with a globular polytopic ligand constructed around the fullerene scaffold, an N-alkyl analogue of 1-deoxynojirimycin was selected as the peripheral ligand. This class of compounds is indeed poorly selective and displays modest to good glycosidase inhibition. It was thus anticipated that these compounds could be excellent models for the examination of the influence of multivalency on inhibition selectivity over a large range of glycosidases. In addition, the alkyl chain on the endocyclic nitrogen atom of the iminosugar is an ideal spacer that may allow for easy grafting onto the central C60 core by means of a cycloaddition reaction. [16] The synthesis of the azide building block is based on the optimization of a strategy reported independently by Overkleeft et al. and Vasella and co-workers. As shown in Scheme 1, the d-hydroxy amide 2 was obtained directly from commercially available tetra-O-benzyl d-glucopyranose (1) in 78% yield by oxidative amidation with iodine in 30% aqueous ammonia (30%). The main advantage of this onepot process is that aldehyde oxidation and C N bond formation are performed in a single synthetic step. Oxidation of the hydroxy group at C5 followed by intramolecular [*] Prof. P. Compain, C. Decroocq, Dr. D. Hazelard Laboratoire de Synth se Organique et Mol cules Bioactives Universit de Strasbourg et CNRS (UMR 7509) Ecole Europ enne de Chimie, Polym res et Mat riaux 25 rue Becquerel, 67087 Strasbourg (France) Fax: (+ 33)3-6885-2754 E-mail: philippe.compain@unistra.fr

Design and Synthesis of Highly Potent and Selective Pharmacological Chaperones for the Treatment of Gaucher's disease

The chemical-chaperone approach is an emerging concept in drug research that holds promise for the treatment of inherited diseases caused by improperly folded proteins. This strategy is based on the capacity of certain low-molecular-weight compounds to stabilize or alter the three-dimensional architecture of defective proteins. Recently, the effectiveness of the chemical-chaperone concept has been demonstrated in the field of lysosomal-storage disorders, a group of more than 40 rare diseases that are characterized by the deficiency of the glycosidases involved in the catabolism of glycosphingolipids in the lysosome. In 1999, it was reported that the residual agalactosidase A activity in the lymphoblasts of patients with Fabry disease could be significantly enhanced by using iminosugar-based inhibitors of the deficient glycosidase at subinhibitory concentrations. This “nonintuitive” result can be explained by the fact that, even though the defective enzyme is predisposed to misfolding and/or instability, it is still catalytically active. Reversible competitive inhibitors positively influence the folding state of the abnormal enzyme, thus preventing its degradation by quality control in the endoplasmic reticulum (ER) and ER-associated degradation (ERAD) before its transfer to lysosomes. According to the so-called threshold theory, the severity of the disease correlates with the residual degrading capacity in the patients’ lysosomes and, therefore, even a slight elevation in enzyme activity can lead to a significant improvement in the symptoms associated with a lysosomal-storage disorder. Active-site-specific chaperone strategies are being evaluated clinically for the treatment of Fabry disease, thus highlighting their strong potential as a new therapeutic option for these disorders. Recent studies have shown that this approach may be applied to Gaucher’s disease, the most prevalent lysosomal-storage disorder. 7] This autosomal recessive disease is caused by a deficiency of glucosylceramide b-glucosidase, also called bglucocerebrosidase, (GCase) that leads to the accumulation of undegraded glucosylceramide (GlcCer), especially in macrophages, and to severe symptoms. In type 1, the mildest and most common of the three clinical forms of Gaucher’s disease, patients suffer from bone pain, skeletal lesions, anaemia and liver or spleen damage. The first-line treatment for Gaucher’s disease is based on the administration of CerezymeA, a recombinant form of GCase, to supplement the defective hydrolytic enzyme. A second strategy makes use of a small molecule, N-butyl-1-deoxynojirimycin 1 (NB-DNJ, ZavescaA), to inhibit the biosynthesis of GlcCer.

The Multivalent Effect in Glycosidase Inhibition: Probing the Influence of Architectural Parameters with Cyclodextrin-based Iminosugar Click Clusters

In contrast to most lectins, glycosidases may appear to be unpromising targets for multivalent binding because they display only a single active site. To explore the potential of multivalency on glycosidase inhibition, unprecedented cyclodextrin-based iminosugar conjugates have been designed and prepared. The synthesis was performed by way of Cu(I) -catalyzed azide-alkyne cycloaddition reaction under microwave activation between propargylated multivalent β-cyclodextrins and an azide-armed N-alkyl 1-deoxynojirimycin derivative. Evaluation with a panel of glycosidases of this new class of glycomimetic clusters revealed the strongest affinity enhancement observed to date for a multivalent glycosidase inhibitor, with binding enhancement up to four orders of magnitude over the corresponding monovalent ligand for α-mannosidase. These results demonstrate that the multivalency concept extends beyond carbohydrate-lectin recognition processes to glycomimetic-enzyme inhibition.

Second-Generation Iminoxylitol-Based Pharmacological Chaperones for the Treatment of Gaucher Disease

A series of O‐alkyl iminoxylitol derivatives was synthesized and evaluated as β‐glucocerebrosidase (GCase) inhibitors. This structure–activity study shows a dramatic influence of the position of the alkyl chain (α‐C1, O2, O3, or O4) on human GCase inhibition. Remarkably, 1,2‐shift of the alkyl chain from C1 to O2 was found to maintain high inhibitory potency toward GCase as well as chaperone activity at sub‐inhibitory concentration (10 nM). Removal of the stereogenic center at the pseudo‐anomeric position led to shorter and more practical synthetic sequences. 2‐O‐Alkyl iminoxylitol derivatives constitute a new promising class of leads for the treatment of Gaucher disease by means of pharmacological chaperone therapy.

First total synthesis of (+)-hyacinthacine A2

Abstract The first synthesis of (+)-hyacinthacine A 2 has been achieved in six steps from 2,3,5-tri- O -benzyl- d -arabinofuranose in an overall yield of 11%. The structure of this natural product was thus unambiguously established as (1 R, 2 R, 3 R, 7a R )-1,2-dihydroxy-3-hydroxymethylpyrrolizidine.

The Multivalent Effect in Glycosidase Inhibition: A New, Rapidly Emerging Topic in Glycoscience

A bunch of keys, one lock: The multivalent effect in glycosidase inhibition is a new, rapidly emerging area with exciting potential and scope. This review presents a description of the different types of neoglycoclusters and their evaluation as glycosidase inhibitors. The first promising therapeutic applications are discussed, as well as the mechanisms underlying the observed inhibitory multivalent effect.

Iminosugar-based glycopolypeptides: glycosidase inhibition with bioinspired glycoprotein analogue micellar self-assemblies.

Biomimetic nanoparticles prepared by self-assembly of iminosugar-based glycopolypeptides evidenced remarkable multivalency properties when inhibiting α-mannosidase activity. This approach paves the way to obtain biologically active drug delivery systems having glycosidase inhibition potency.

Cyclodextrin-based iminosugar click clusters: the first examples of multivalent pharmacological chaperones for the treatment of lysosomal storage disorders.

The pharmacological chaperone concept has recently raised many hopes for the treatment of inherited diseases that are caused by improperly folded proteins. The most relevant successes have undoubtedly been obtained in the field of glycosphingolipid lysosomal storage disorders (GLSDs), a small group of diseases characterized by a deficiency of the glycosidases involved in the catabolism of glycosphingolipids in the lysosome. Pharmacological chaperone therapy is based on the ability of reversible inhibitors of the deficient enzymes to enhance their residual hydrolytic activity at sub-inhibitory concentrations. The proof-of-concept of this approach was demonstrated in 1999 with 1-deoxygalactonojirimycin (1, Amigal), a potent inhibitor of the galactosidase involved in Fabry disease (Scheme 1). The counterintuitive basis of the pharmacological