Towards new cholera prophylactics and treatment: Crystal structures of bacterial enterotoxins in complex with GM1 mimics.

Cholera is a life-threatening disease in many countries, and new drugs are clearly needed. C-glycosidic antagonists may serve such a purpose. Here we report atomic-resolution crystal structures of three such compounds in complexes with the cholera toxin. The structures give unprecedented atomic details of the molecular interactions and show how the inhibitors efficiently block the GM1 binding site. These molecules are well suited for development into low-cost prophylactic drugs, due to their relatively easy synthesis and their resistance to glycolytic enzymes. One of the compounds links two toxin B-pentamers in the crystal structure, which may yield improved inhibition through the formation of toxin aggregates. These structures can spark the improved design of GM1 mimics, either alone or as multivalent inhibitors connecting multiple GM1-binding sites. Future developments may further include compounds that link the primary and secondary binding sites. Serving as decoys, receptor mimics may lessen symptoms while avoiding the use of antibiotics.

Synthesis and affinity evaluation of a small library of bidentate cholera toxin ligands: towards nonhydrolyzable ganglioside mimics.

A small library of nonhydrolyzable mimics of GM1 ganglioside, featuring galactose and sialic acid as pharmacophoric carbohydrate residues, was synthesized and tested. All compounds were synthesized from readily available precursors using high-performance reactions, including click chemistry protocols, and avoiding O-glycosidic bonds. Some of the most active molecules also feature a point of further derivatization that can be used for conjugation with polyvalent aglycons. Their affinity towards cholera toxin was assessed by weak affinity chromatography, which allowed a systematic evaluation and selection of the best candidates. Affinity could be enhanced up to one or two orders of magnitude over the affinity of the individual pharmacophoric sugar residues.

Interfering with the sugar code: design and synthesis of oligosaccharide mimics.

Oligosaccharide determinants of cellular glycoconjugates interact with protein receptors triggering a variety of cellular responses within a wide range of physiological and pathological processes and with exquisitely tuned selectivity. This has led to the formulation of the hypothesis that a sugar code exists and that sugar-binding proteins (lectins) act to decipher it and translate it into biological responses. Interference with these recognition events by functional mimics of carbohydrates could thus be used to modulate or alter signal transmission, or to prevent the onset of diseases. Attempts to design and prepare glycomimetic inhibitors of well-known target lectins (cholera toxin, DC-SIGN) are reviewed in this concept paper.

Direct epoxidation of D-glucal and D-galactal derivatives with in situ generated DMDO.

A multi-gram epoxidation of 3,4,6-tri-O-benzyl-D-glucal and D-galactal with dimethyldioxirane (DMDO) generated in situ from Oxone/acetone in a biphasic system (CH(2)Cl(2)-aqueous NaHCO(3)) resulted in the formation of the corresponding 1,2-anhydrosugars in a 99% yield and 100% selectivity. In a similar way, 3,4,6-tri-O-acetyl-D-glucal afforded a 7:1 mixture of the corresponding gluco and manno derivatives in an 87% overall yield.

First synthesis of 1,2,3-triazolo-linked (1,6)-alpha-D-oligomannoses (triazolomannoses) by iterative Cu(I)-catalyzed alkyne-azide cycloaddition.

The iterative copper(I)-catalyzed cycloaddition (rt or microwave) between an ethynyl alpha-C-mannoside and alkyl 6-azido-alpha-C-mannoside derivatives was suited to the (1,6)-ligation between alpha-D-mannose units through 1,4-disubstituted triazole bridges, thus resulting in the formation of linear oligomers (80-90% yield) with alternating triazole and mannose fragments up to a triazolo-pentamannose derivative.