David Rodriguez-Lucena

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.

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

Rescue of Functional CFTR Channels in Cystic Fibrosis: A Dramatic Multivalent Effect Using Iminosugar Cluster-Based Correctors

Cystic fibrosis is caused by a mutation in the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. N‐butyl 1‐deoxynojirimycin (N‐Bu DNJ), a clinical candidate for the treatment of cystic fibrosis, is able to act as a CFTR corrector by overcoming the processing defect of the mutant protein. To explore the potential of multivalency on CFTR correction activity, a library of twelve DNJ click clusters with valencies ranging from 3 to 14 were synthesized. Significantly, the trivalent analogues were found to be up to 225‐fold more potent than N‐Bu DNJ and up to 1000‐fold more potent than the corresponding monovalent models. These results provide the first description of a multivalent effect for correcting protein folding defects in cells and should have application for the treatment of a number of protein folding disorders. Preliminary mechanistic studies indicated that CFTR correction activity enhancement was not due to a multivalent effect in ER‐glucosidase inhibition or to a different mode of action of the multivalent iminosugars.

Regioselective Double Capping of Cyclodextrin Scaffolds

Four different regioselective double capping reactions were applied either to α- or β-cyclodextrin (CD) scaffolds. The first, which relied on the use of a rigid, bulky dialkylating reagent containing two trityl-like subunits, gave access to an A,B,D,E-tetrafunctionalised β-CD regioisomer in large scale reactions. Two further capping reactions, involving the dianions PhP(2-) and S(2- , led to the synthesis of new C(1)-symmetrical β-cyclodextrins in which pairs of neighbouring glucose units are linked by very short spacers. The last double capping reaction described allowed the high-yield preparation of unprecedented α- and β-cyclodextrins containing two sulfate handles. Proximal capping turned out to be favoured for each of the above difunctional reagents. The structural characterisation of the capped species was achieved by thorough NMR investigations as well as by single-crystal X-ray diffraction studies.

Synthesis of Azide-armed α-1-C-Alkyl-imino-d-xylitol Derivatives as Key Building Blocks for the Preparation of Iminosugar Click Conjugates

Azide-armed α-1-C-alkyl-imino-d-xylitol derivatives have been efficiently prepared by way of olefin cross-metathesis in eight to nine steps and in an overall yield of 19% to 26% from 2,3,4-tri-O-benzyl-d-xylopyranose. Optimization of cleavage conditions of N-NAP-protected tertiary amines using DDQ in CH2Cl2-H2O (18:1) is also reported. The iminosugars synthesized will be used as key building blocks in the synthesis of multivalent iminosugars of biological interest by way of Cu(I)-catalyzed azide-alkyne cycloaddition reaction.

Promoting helicity in carbohydrate-containing foldamers through long-range hydrogen bonds

A sensor system to probe the propensity of carbohydrates to induce helical structures through long-range hydrogen bonds, based on a C(2)-symmetric xylylene bis(thiourea) arrangement, is reported; the formation of intermolecular complexes with benzoate anion promotes helix uncoiling, the free energy of the process being related to helix stability.

Synthesis and biological properties of iron chelators based on a bis-2-(2-hydroxy-phenyl)-thiazole-4-carboxamide or -thiocarboxamide (BHPTC) scaffold

Bis-2-(2-hydroxy-phenyl)-thiazole-4-carboxamides and -thiocarboxamides (BHPTCs) form a family of gemini hexacoordinated bis-tridentate chelating scaffolds. Four molecules were synthesized and shown to chelate iron(III) efficiently with a 1:1 stoichiometry. A dithioamide BHPTC displayed promising antiproliferative activity in several cancerous cell lines, making this molecule an interesting lead compound for the design of new iron-chelating anticancer drugs. Conversely, diamide BHPTCs had significant cytoprotective activity against iron overload in HepaRG cells in vitro, and were as efficient as and less toxic than deferoxamine B (DFO).