Jérôme Désiré

Catching elusive glycosyl cations in a condensed phase with HF/SbF5 superacid

Glycosyl cations are universally accepted key ionic intermediates in the mechanism of glycosylation, the reaction that covalently links carbohydrates to other molecules. These ions have remained hypothetical species so far because of their extremely short life in organic media as a consequence of their very high reactivity. Here, we report the use of liquid hydrofluoric acid-antimony pentafluoride (HF/SbF5) superacid to generate and stabilize the glycosyl cations derived from peracetylated 2-deoxy and 2-bromoglucopyranose in a condensed phase. Their persistence in this superacid medium allows their three-dimensional structure to be studied by NMR, aided by complementary computations. Their deuteration further confirms the impact of the structure of the glycosyl cation on the stereochemical outcome of its trapping.

Access to l- and d-Iminosugar C-Glycosides from a d-gluco-Derived 6-Azidolactol Exploiting a Ring Isomerization/Alkylation Strategy

A flexible synthetic access to six-membered L- and D-iminosugar C-glycosides is reported starting from the easily available 6-azido-6-deoxy-2,3,4-tri-O-benzyl-D-glucopyranose precursor. This methodology involves a highly diastereoselective tandem ring enlargement/alkylation and a stereocontrolled ring contraction. It allows an efficient synthesis of iminosugar C-glycosides displaying structural diversity at both C-1 and C-6.

Novel imino sugar α-glucosidase inhibitors as antiviral compounds.

Deoxynojirimycin (DNJ) based imino sugars display antiviral activity in the tissue culture surrogate model of Hepatitis C (HCV), bovine viral diarrhoea virus (BVDV), mediated by inhibition of ER α-glucosidases. Here, the antiviral activities of neoglycoconjugates derived from deoxynojirimycin, and a novel compound derived from deoxygalactonojirimycin, by click chemistry with functionalised adamantanes are presented. Their antiviral potency, in terms of both viral infectivity and virion secretion, with respect to their effect on α-glucosidase inhibition, are reported. The distinct correlation between the ability of long alkyl chain derivatives to inhibit ER α-glucosidases and their anti-viral effect is demonstrated. Increasing alkyl linker length between DNJ and triazole groups increases α-glucosidase inhibition and reduces the production of viral progeny RNA and the maturation of the envelope polypeptide. Disruption to viral glycoprotein processing, with increased glucosylation on BVDV E2 species, is representative of α-glucosidase inhibition, whilst derivatives with longer alkyl linkers also show a further decrease in infectivity of secreted virions, an effect proposed to be distinct from α-glucosidase inhibition.

Synthesis of 1,2-trans-2-Acetamido-2-deoxyhomoiminosugars

The first synthesis of 1,2-trans-homoiminosugars devised as mimics of β-D-GlcNAc and α-D-ManNAc is described. Key steps include a regioselective azidolysis of a cyclic sulfite and a β-amino alcohol skeletal rearrangement applied to a polyhydroxylated azepane. The β-D-GlcNAc derivative has been coupled to serine to deliver an iminosugar C-amino acid. The two homoiminosugars demonstrate moderate glycosidase inhibition.

Synthesis of 1,2-cis-homoiminosugars derived from GlcNAc and GalNAc exploiting a β-amino alcohol skeletal rearrangement.

The synthesis of 1,2-cis-homoiminosugars bearing an NHAc group at the C-2 position is described. The key step to prepare these α-D-GlcNAc and α-D-GalNAc mimics utilizes a β-amino alcohol skeletal rearrangement applied to an azepane precursor. This strategy also allows access to naturally occurring α-HGJ and α-HNJ. The α-D-GlcNAc-configured iminosugar was coupled to a glucoside acceptor to yield a novel pseudodisaccharide. Preliminary glycosidase inhibition evaluation indicates that the α-D-GalNAc-configured homoiminosugar is a potent and selective α-N-acetylgalactosaminidase inhibitor.

Synthesis, Conformational Analysis, and Evaluation as Glycosidase Inhibitors of Two Ether-Bridged Iminosugars

Two bicyclic iminosugars have been synthesized from polyhydroxylated azepanes by ring isomerization followed by debenzylative cyclization. Their conformations have been studied by NMR and molecular modeling and their glycosidase inhibition profiles were determined. They both adopt a chair conformation for the piperidine ring and display weak inhibition on α-glucosidases.

HF-Induced Intramolecular C-Arylation and C-Alkylation/Fluorination of 2-Aminoglycopyranoses

Internal C-aryl and C-alkyl glycosides derived from 2-aminoglycopyranoses have been synthesized, exploiting a HF-mediated stereoselective intramolecular glycosylation. These conditions are compatible with acetate protecting groups and allow introduction of aromatics with various electronic distributions at the anomeric position. This strategy also provides straightforward entry to original fluorinated sugar-azacycle hybrids via a tandem internal C-glycosylation/fluorination reaction starting from 2-N-allyl/propargyl glycopyranoses. All cyclizations proceed in a 1,2-cis stereocontrolled manner.

Multivalency to inhibit and discriminate hexosaminidases

A set of multivalent polyhydroxylated acetamidoazepanes based on ethylene glycol, glucoside, or cyclodextrin scaffolds was prepared. The compounds were assessed against plant, mammalian, and therapeutically relevant hexosaminidases. Multimerization was shown to improve the inhibitory potency with synergy, and to fine tune the selectivity profile between related hexosaminidases.

Synthetic deoxynojirimycin derivatives bearing a thiolated, fluorinated or unsaturated N-alkyl chain: identification of potent α-glucosidase and trehalase inhibitors as well as F508del-CFTR correctors

The synthesis of eleven 1-deoxynojirimycin (DNJ) derivatives presenting either a monofluoro, difluoro, thiolated or unsaturated N-alkyl chain of various length is described. Exploiting the unsaturated moiety on the nitrogen, fluorine has been introduced through a HF/SbF5 superacid catalysed hydrofluorination and thiol-ene click chemistry allowed introduction of sulfur. The synthetic derivatives have been tested for their ability to inhibit glycosidases and correct F508del-CFTR. Two of the unsaturated iminosugars exhibited potency similar to Miglustat as F508del-CFTR correctors. The thioalkyl iminosugars as well as the corresponding alkyl iminosugars demonstrated low micromolar α-glucosidases and trehalases inhibition. Introduction of fluorine abolished F508del-CFTR correction and trehalase inhibition.

Synthesis of pyrrolidine-based analogues of 2-acetamidosugars as N-acetyl-d-glucosaminidase inhibitors

A ring-contraction strategy applied to β-azido,γ-hydroxyazepanes yielded after functional group manipulation new tetrahydroxylated pyrrolidines displaying an acetamido moiety, one of these iminosugars demonstrating low micromolar inhibition on N-acetylglucosaminidases.