Denis Giguère

Carbohydrate triazoles and isoxazoles as inhibitors of galectins-1 and -3

Galactosides and lactosides bearing triazoles or isoxazoles, regiospecifically prepared by [1,3]-dipolar cycloadditions between alkynes, azides or nitrile oxides, provided specific galectin-1 and -3 inhibitors with potencies as low as 20 microM.

Combining Glycomimetic and Multivalent Strategies toward Designing Potent Bacterial Lectin Inhibitors

As part of ongoing activities toward the design of potent and selective ligands against galactoside-binding proteins from animal, bacterial, and plant lectins, a systematic investigation involving the synthesis and binding evaluations of a series of original β-C-galactopyranoside mimetics is described. The multivalent presentation of partly optimized candidates on various dendritic scaffolds through Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAc) has also been achieved. Biophysical investigations based on isothermal titration calorimetry (ITC) have indicated a dissociation constant in the low micromolar range for the best optimized monovalent conjugate (K(d)=37 μM). The results thus confirmed that stable C-galactosides could represent efficient synthetic glycomimetics of natural α-linked oligosaccharidic inhibitors of PA-IL lectin (Lec A) from the pathogenic Pseudomonas aeruginosa. Striking enhancements in the avidity of the glycoconjugates were also observed for tri-, hexa-, and nonavalent derivatives, among which the most potent exhibited dissociation constants below 500 nM, corresponding to a 400-fold increase in affinity compared with the β-D-Gal-O-Me used as reference. To deepen our understanding of the binding mode of the best glycomimetics involved in the recognition process, molecular modeling studies, docking calculations, and NMR diffusion measurements have been performed. Although favorable complementary interactions induced by the addition of the hydrophobic aglycon might explain the affinity enhancement, experimental determination of the size and the topology of the multivalent conjugates further supported the formation of aggregative complexes as a major multivalent binding mode. This work represents a systematic and comprehensive study towards a thorough understanding of the protein-carbohydrate interactions involved in Pseudomonas aeruginosa infection, and as such should prove useful for the development of stable and optimized anti-adhesive agents.

Total Synthesis of Epicoccin G

An expedient enantioselective total synthesis of epicoccin G and related dithiodiketopiperazines through a strategy featuring direct two-directional sulfenylation, photooxygenation, and Kornblum-DeLaMare rearrangement is described.

Synthesis of stable and selective inhibitors of human galectins-1 and -3.

The syntheses of glycolytically stable galactosides and lactosides have been made toward the selective inhibition of human galectins-1 and -3. Transition metal-catalyzed cross-coupling reactions were used to create carbon-carbon bond formation (Sonogashira, Suzuki, Heck, Glaser). Additionally, Hantzsch condensation was used to create novel 2-aminothiazoles which reacted with a panel of acylating and sulfonylating reagents. Moreover, dimeric galactosides and lactosides bearing triazoles, regiospecifically prepared using copper-catalyzed Huisgen azide-alkyne [1,3]-dipolar cycloaddition, provided efficient galectins-1 and -3 inhibitors. Best monovalent inhibitor among the tested series was (E)-methyl 2-phenyl-4-(beta-D-galactopyranosyl)-but-2-enoate 15 with inhibitory potency of 313 microM against galectin-1 and best dimers were bis-lactoside 68 and 75 having both inhibitory properties of 160 microM against Galectin-3.

Aromatic Thioglycoside Inhibitors Against the Virulence Factor Leca from Pseudomonas Aeruginosa.

Three small families of hydrolytically stable thioaryl glycosides were prepared as inhibitors of the LecA (PA-IL) virulence factor corresponding to the carbohydrate binding lectin from the bacterial pathogen Pseudomonas aeruginosa. The monosaccharidic arylthio β-d-galactopyranosides served as a common template for the major series that was also substituted at the O-3 position. Arylthio disaccharides from lactose and from melibiose constituted the other two series members. In spite of the fact that the natural ligand for LecA is a glycolipid of the globotriaosylceramide having an α-d-galactopyranoside epitope, this study illustrated that the β-d-galactopyranoside configuration having a hydrophobic aglycon could override the requirement toward the anomeric configuration of the natural sugar. The enzyme linked lectin assay together with isothermal titration microcalorimetry established that naphthyl 1-thio-β-d-galactopyranoside () gave the best inhibition with an IC50 twenty-three times better than that of the reference methyl α-d-galactopyranoside. In addition it showed a KD of 6.3 μM which was ten times better than that of the reference compound. The X-ray crystal structure of LecA with was also obtained.

Synthesis and screening of a small glycomimetic library for inhibitory activity on medically relevant galactoside-specific lectins in assays of increasing biorelevance

Synthetic introduction of aglyconic substitutions into carbohydrate ligands is an approach toward identifying potent inhibitors of medically relevant lectins. We tested a panel of 27 galactoside/lactoside derivatives harboring varying aglycone moieties together with some O-3/O-3′ functionality toward a biohazardous plant toxin and four human adhesion/growth-regulatory galectins. Differential sensitivity profiles of lectin binding with cases showing activity increase relative to galactose/lactose were revealed by systematic assessments using a solid-phase assay. Quantitative differences between the homologous human proteins could even be detected. Binding of substituted lactosides to galectins-1 and -3 was shown to be enthalpically driven. To determine the potential of substituted glycosides to protect cells from harmful lectin association, binding assays with human tumor cells were performed. Invariably, compounds were identified with increased potency relative to the unsubstituted parent sugars. However, aglyconic substitutions were shown to be able to convey cytotoxicity. This report directs further attention to examining additional 2′- and 3′-substitutions of the galactose core and the potential of ligand presentation in glycoclusters to enhance avidity and selectivity, continuing to use the herein applied strategic combination of a convenient biochemical test system with bioassays.

A Practical Sulfenylation of 2,5-Diketopiperazines†

Sulfurs in action A practical and simple method for the introduction of sulfur atoms into 2,5-diketopiperazines (I) under mild conditions has been developed leading to more or less complex epidithiodiketopiperazines (II) and bis-methylthiodiketopiperazines (III).

Galectin-1-Specific Inhibitors as a New Class of Compounds To Treat HIV-1 Infection

ABSTRACT Despite significant improvements, antiretroviral therapies against HIV-1 are plagued by a high frequency of therapeutic failures that have been associated with acquisition of drug resistance. We recently reported that HIV-1 exploits a host glycan binding protein, galectin-1, to increase its attachment to host cells, thereby increasing its overall infectivity in susceptible cells. This finding suggests that host molecules such as galectin-1 could reduce the expected efficiency of HIV-1 drugs targeting early steps of the replicative cycle, such as attachment and entry processes. Thus, new classes of drugs that would interfere with galectin-1/HIV-1 interactions could benefit the current antiretroviral therapy. To further explore this possibility, experiments were conducted to discover leading compounds showing specific inhibition of galectin-1 activity in a cellular model of HIV-1 infection. Three lactoside compounds were found to modestly inhibit the interaction of galectin-1 with primary human CD4+ T cells. Interestingly, these same inhibitors reduced the galectin-1-mediated increase in HIV-1 attachment to target cells in a much more efficient manner. More important, the tested lactoside derivatives also significantly decreased the galectin-1-dependent enhancement of HIV-1 infection. These observations deserve further attention when considering that the development of new drugs to prevent and treat HIV-1 infection remains a priority.

En route to a carbohydrate-based vaccine against Burkholderia cepacia

We report a very high yielding first total synthesis of trisaccharide 5, alpha-D-Rhap-(1 --> 3)-alpha-D-Rhap-(1 --> 4)-alpha-D-Galp, corresponding to the repeating unit 1 of an O-polysaccharide present in the lipopolysaccharide of clinical isolate of Burkholderia cepacia. The approach included two successive glycosylations, based on D-rhamnosyl trichloroacetimidate donors 12 and 14. The oligosaccharide 5 has been further functionalized by photochemical coupling or cross-metathesis with non-natural amino acid derivatives. Trisaccharidylamino acids 16 and 17 are now available, with the aim of preparing a novel synthetic carbohydrate-based vaccine.

Domino Heck/lactonization-catalyzed synthesis of 3-C-linked mannopyranosyl coumarins.

Selective syntheses of methyl alpha- (8) and beta-C-mannopyranosyl acrylates (9) were obtained from alpha-C-allyl mannopyranoside (3) by ozonolysis to 4 followed by alpha-methylenation to provide intermediate aldehydes 5 and 6. The beta-anomer 6 was obtained by in situ anomeric epimerization. The acrylates and the homologous alpha-anomer 16, obtained by oxidative hydroboration, oxidation, and alpha-methylenation, were converted into 3-C-linked mannopyranosyl coumarins 11, 12, and 19 in good yields under one-pot Heck/lactonization conditions.