Multivalency plays a major role in biological processes and particularly in the relationship between pathogenic microorganisms and their host that involves protein-glycan recognition. These interactions occur during the first steps of infection, for specific recognition between host and bacteria, but also at different stages of the immune response. The search for high-affinity ligands for studying such interactions involves the combination of carbohydrate head groups with different scaffolds and linkers generating multivalent glycocompounds with controlled spatial and topology parameters. By interfering with pathogen adhesion, such glycocompounds including glycopolymers, glycoclusters, glycodendrimers and glyconanoparticles have the potential to improve or replace antibiotic treatments that are now subverted by resistance. Multivalent glycoconjugates have also been used for stimulating the innate and adaptive immune systems, for example with carbohydrate-based vaccines. Bacteria present on their surfaces natural multivalent glycoconjugates such as lipopolysaccharides and S-layers that can also be exploited or targeted in anti-infectious strategies.

Glycan recognition by lectins initiates clinically relevant processes such as toxin binding or tumor spread. Thus, the development of potent inhibitors has a medical perspective. Toward this goal, we report the synthesis of both rigid and flexible bivalent lactosides on scaffolds that include secondary and tertiary terephthalamides and N,N 0 -diglucosylterephthalamides. Construction of these compounds involved Schmidt-Michel glycosidation, and amide coupling or Ugi reactions of relevant glycosyl amines in key steps. A glycocluster based on a rigid glycophane was also prepared from coupling of a glucuronic acid derivative and p-xylylenediamine with subsequent ring-closing metathesis. Finally, a more flexible bivalent lactoside was produced from lactosyl azide with use of the copper-catalyzed azide-alkyne cycloaddition. Distances between lactose residues were analyzed computationally as were their orientations for the relatively rigid subset of compounds. Distinct spacing properties were revealed by varying the structure of the scaffold or by varying the location of the lactose residue on the scaffold. To relate these features to bioactivity a plant toxin and human adhesion/growth-regulatory galectins were used as sensors in three types of assay, i.e. measuring agglutination of erythrocytes, binding to glycans of a surface-immobilized glycoprotein, or binding to human cells. Methodologically, the common hemeagglutination assay was found to be considerably less sensitive than both solid-phase and cell assays. The bivalent compounds were less effective at interfering with glycoprotein binding to the plant toxin than to human lectins. Significantly, a constrained compound was identified that displayed selectivity in its inhibitory potency between galectin-3 and its proteolytically processed form. Conversely, compounds with a high degree of flexibility showed notable ability to protect human cells from plant toxin binding. The applied conjugation chemistry thus is compatible with the long-term aim to produce potent and selective lectin inhibitors.

Fungal infections with increasing resistance to conventional therapies are a growing concern. Candida albicans is a major opportunistic yeast responsible for mucosal and invasive infections. Targeting the initial step of the infection process (i.e., C. albicans adhesion to the host cell) is a promising strategy. A wide variety of molecules can interfere with adhesion processes via an assortment of mechanisms. Herein, we focus on how small molecules disrupt biosynthesis of fungal cell wall components and membrane structure, prevent the localization of GPI-anchor proteins, inhibit production of enzymes involved in adhesion, downregulate genes encoding adhesins and competitively inhibit receptor interactions. As a result, adhesion of C. albicans to host cells is reduced, paving the way to new classes of antifungal agents.

Trypanosoma cruzi and Leishmania amazonensis are the causative agents of Chagas' disease and leishmaniasis, respectively. These conditions affect millions of people worldwide, especially in developing countries. As such, there is an urgent need for novel, efficient and cost-effective treatments for these diseases, given the growing resistance and side-effects of current therapies. This work details the synthesis and evaluation of the anti-parasitic activity of novel amino- and iminopyridyl metal chelators, their glycosylated derivatives and some of their metal complexes. Our results revealed the potent and metal-dependent activity for the aminopyridyl compounds: Cu(ii) complexes were most effective against T. cruzi trypomastigotes, while Zn(ii) complexes presented excellent activity against L. amazonensis promastigotes. In addition, the compounds showed excellent selectivity indexes and very low relative toxicity as judged by in vitro and in vivo studies, respectively, using RAW macrophages and Galleria mellonella larvae model.

The conjugation of carbohydrates to synthetic scaffolds has the goal of preparing potent inhibitors of lectin binding. We herein report the synthesis of a panel of bivalent compounds (cyclophane and terephthalamide-derivatives) then used to establish the influence of scaffold flexibility on respective inhibitory potency in a medically relevant test system. Synthetic routes to two phenylenediamine-based glycocyclophanes involving Ugi reactions of glucuronic acid derivatives and subsequent ring closing metathesis are described, as are improvements for producing terephthalamide-based carbohydrate carriers. Assays were performed with human tumour cells measuring quantitatively the influence of the test compounds on fluorescent surface staining by labelled lectins. Biological evaluation using two different lines of cancer cells as well as cells with known alterations in the glycomic profile (cells treated with an inhibitor of glycan processing and a glycosylation mutant) reduced the risk of generating premature generalizations regarding inhibitor potency. Bioactivity relative to free mannose was invariably determined for the synthetic compounds. A clear trend for enhanced inhibitory properties for macrocyclic compounds compared to non-macrocyclic derivatives was discerned for one type of glycocyclophane. Herein we also document the impact of altering the spacing between the mannose residues, altering cell surface ligand density and cell-type reactivity. The applied strategy for the cell assays is proposed to be of general importance in the quest to identify medically relevant lectin inhibitors.