Anne Bodlenner

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.

A systematic investigation of iminosugar click clusters as pharmacological chaperones for the treatment of Gaucher disease.

A series of 18 mono‐ to 14‐valent iminosugars with different ligands, scaffolds, and alkyl spacer lengths have been synthesized and evaluated as inhibitors and pharmacological chaperones of β‐glucocerebrosidase (GCase). Small but significant multivalent effects in GCase inhibition have been observed for two iminosugar clusters. Our study provides strong confirmation that compounds that display the best affinity for GCase are not necessarily the best chaperones. The best chaperoning effect observed for a deprotected iminosugar cluster has been obtained with a tetravalent 1‐deoxynojirimycin (DNJ) analogue (3.3‐fold increase at 10 μM). In addition, our study provides the first evidence of the high potential of prodrugs for the development of potent pharmacological chaperones. Acetylation of a trivalent DNJ derivative, to give the corresponding acetate prodrug, leads to a pharmacological chaperone that produces higher enzyme activity increases (3.0‐fold instead of 2.4‐fold) at a cellular concentration (1 μM) reduced by one order of magnitude.

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

Summary Cyclic N-propargyl α-peptoids of various sizes were prepared by way of macrocyclizations of linear N-substituted oligoglycines. These compounds were used as molecular platforms to synthesize a series of iminosugar clusters with different valency and alkyl spacer lengths by means of Cu(I)-catalysed azide–alkyne cycloadditions. Evaluation of these compounds as α-mannosidase inhibitors led to significant multivalent effects and further demonstrated the decisive influence of scaffold rigidity on binding affinity enhancements.

Iminosugar-Cyclopeptoid Conjugates Raise Multivalent Effect in Glycosidase Inhibition at Unprecedented High Levels

A series of cyclopeptoid-based iminosugar clusters has been evaluated to finely probe the ligand content-dependent increase in α-mannosidase inhibition. This study led to the largest binding enhancement ever reported for an enzyme inhibitor (up to 4700-fold on a valency-corrected basis), which represents a substantial advance over the multivalent glycosidase inhibitors previously reported. Electron microscopy imaging and analytical data support, for the best multivalent effects, the formation of a strong chelate complex in which two mannosidase molecules are cross-linked by one inhibitor.

Understanding multivalent effects in glycosidase inhibition using C-glycoside click clusters as molecular probes

The synthesis of the first examples of multivalent C-glycosides based on C60-fullerene or β-cyclodextrin cores by way of Cu(I)-catalyzed azide–alkyne cycloadditions is reported. These compounds were designed as molecular probes to understand the mechanisms underlying the outstanding multivalent effects observed in glycosidase inhibition. The inhibition results obtained support a multivalent-binding model based on two scenarios both involving nonspecific interactions and varying by the presence or the absence of active site specific interactions. The magnitude of the multivalent effect obtained depends on the identity of the glycosidase involved and more specifically on the accessibility of its catalytic active site. Large inhibitory multivalent effects can be obtained when both glycosidase active sites and non-catalytic sites at the protein surface are involved in binding events. On the other hand, nonspecific interactions alone are not sufficient to achieve relative affinity enhancements exceeding a simple statistical effect (i.e., a relative inhibition potency not better than one on a valence-corrected basis).

Synthesis and characterisation of immunogens for the production of antibodies against small hydrophobic molecules with biosignature properties

In the present study, five different classes of small hydrophobic molecular targets, atypical for antibody generation, were structurally modified in order to introduce suitable reactive functionalities and/or spacers which allow covalent coupling to a carrier protein resulting in a stable carrier-hapten complex. These targets were chosen to serve as markers of extant and/or extinct life in the context of the development of the Life Marker Chip (LMC), an antibody-based instrument, which is being developed by a UK-led international consortium for flight to Mars on board the joint ESA/NASA Mars exploration ExoMars mission. The hapten-protein conjugates were designed to be used as immunogens for antibody generation and immunoassay reagents in subsequent stages of the LMC development. The extent of protein modification due to covalent attachment of hapten was determined by two independent methods, i.e. trinitrobenzenesulfonic acid (TNBSA) titrations of remaining protein reactive groups and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of the resultant hapten-protein conjugates. In a further quality validation step, the conjugates were presented to an animals immune system and polyclonal antibody titres with moderate specificity were obtained. These results suggest that conjugates synthesized as described herein can successfully be used in the generation of antibodies targeting small hydrophobic molecules.

Toward a Molecular Lego Approach for the Diversity-Oriented Synthesis of Cyclodextrin Analogues Designed as Scaffolds for Multivalent Systems.

A modular strategy has been developed to access a diversity of cyclic and acyclic oligosaccharide analogues designed as prefunctionalized scaffolds for the synthesis of multivalent ligands. This convergent approach is based on bifunctional sugar building blocks with two temporarily masked functionalities that can be orthogonally activated to perform Cu(I)-catalyzed azide-alkyne cycloaddition reactions (CuAAC). The reducing end is activated as a glycosyl azide and masked as a 1,6-anhydro sugar, while the nonreducing end is activated as a free alkyne and masked as a triethylsilyl-alkyne. Following a cyclooligomerization approach, the first examples of close analogues of cyclodextrins composed of d-glucose residues and triazole units bound together through α-(1,4) linkages were obtained. The cycloglucopyranoside analogue containing four sugar units was used as a template to prepare multivalent systems displaying a protected d-mannose derivative or an iminosugar by way of CuAAC. On the other hand, the modular approach led to acyclic alkyne-functionalized scaffolds of a controlled size that were used to synthesize multivalent iminosugars.

Design, synthesis and photochemical properties of the first examples of iminosugar clusters based on fluorescent cores

Summary The synthesis and photophysical properties of the first examples of iminosugar clusters based on a BODIPY or a pyrene core are reported. The tri- and tetravalent systems designed as molecular probes and synthesized by way of Cu(I)-catalysed azide–alkyne cycloadditions are fluorescent analogues of potent pharmacological chaperones/correctors recently reported in the field of Gaucher disease and cystic fibrosis, two rare genetic diseases caused by protein misfolding.

Construction of giant glycosidase inhibitors from iminosugar-substituted fullerene macromonomers

An ultra-fast synthetic procedure based on grafting of twelve fullerene macromonomers onto a fullerene hexa-adduct core was used for the preparation of a giant molecule with 120 peripheral iminosugar residues. The inhibition profile of this giant iminosugar ball was evaluated against various glycosidases. In the particular case of the Jack bean α-mannosidase, a dramatic enhancement of the glycosidase inhibitory effect was observed for the giant molecule with 120 peripheral subunits as compared to that of the corresponding mono- and dodecavalent model compounds.

C35 Hopanoid Side Chain Biosynthesis: Reduction of Ribosylhopane into Bacteriohopanetetrol by a Cell‐Free System Derived from Methylobacterium organophilum

The major bacterial triterpenoids of the hopane series each consist of a C30 triterpene hopane moiety and an additional nonterpene C5 side chain derived from D‐ribose and linked through its C‐5 carbon atom to the hopane side chain. Bacteriohopanetetrol and aminobacteriohopanetriol are the most common representatives of this natural product series, adenosylhopane and ribosylhopane being putative precursors. Deuterium‐labelled ribosylhopane was obtained by hemisynthesis and converted into deuterium‐labelled bacteriohopanetetrol in the presence of NADPH, thus giving evidence of this as yet unknown precursor‐to‐product relationship in the bacterial hopanoid metabolic pathway.