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Mannose-binding type 1 pili are important virulence factors for the establishment ofEscherichia coliurinary tract infections (UTIs). These infections are initiated by adhesion of uropathogenicE. colito uroplakin receptors in the uroepithelium via the FimH adhesin located at the tips of type 1 pili. Blocking of bacterial adhesion is able to prevent infection. Here, we provide for the first time binding data of the molecular events underlying type 1 fimbrial adherence, by crystallographic analyses of the FimH receptor binding domains from a uropathogenic and a K-12 strain, and affinity measurements with mannose, common mono- and disaccharides, and a series of alkyl and aryl mannosides. Our results illustrate that the lectin domain of the FimH adhesin is a stable and functional entity and that an exogenous butylα-d-mannoside, bound in the crystal structures, exhibits a significantly better affinity for FimH (Kd = 0.15 µM) than mannose (Kd = 2.3 µM). Exploration of the binding affinities ofα-d-mannosides with longer alkyl tails revealed affinities up to 5 nM. Aryl mannosides and fructose can also bind with high affinities to the FimH lectin domain, with a 100-fold improvement and 15-fold reduction in affinity, respectively, compared with mannose. Taken together, these relative FimH affinities correlate exceptionally well with the relative concentrations of the same glycans needed for the inhibition of adherence of type 1 piliatedE. coli. We foresee that our findings will spark new ideas and initiatives for the development of UTI vaccines and anti-adhesive drugs to prevent anticipated and recurrent UTIs. [ABSTRACT FROM AUTHOR]

Examples of synthetic C-phosphonate analogues of microbial polysaccharide structures containing inter-residue phosphodiester linkages are most rare. The successful construction of such analogues of the Neisseria meningitidis Group A capsular polysaccharide is described. Using a modified Mitsunobu reaction (tris(4-chlorophenyl)phosphine, DIAD, excess of Et3N) between an anomeric C-phosphonate monoester and a 6-OH ManNAc acceptor a high yield (88%) of a dimer was obtained. Transformation of the dimer into a new 6-OH acceptor through deacetylation and further reaction with the elongating C-phosphonate monomer employing the same conditions afforded the trimer in 92% yield. Iteration of the procedure then afforded the tetramer with a coupling yield of 85%. The di-, tri- and tetramer were deprotected to give target structures ready for conjugation to a carrier protein and subsequent immunological evaluation.

By improved (anhydrous) work-up conditions of a triflate displacement reaction, the yield in the preparation of the versatile synthetic intermediate 1,3,4,6-tetra-O-acetyl-2-azido-2-deoxy-alpha-d-mannopyranose has been significantly enhanced. This important precursor is now available in three efficient steps from d-glucose.