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Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is one of the most prevalent infectious diseases. Particularly affected are women, who have a 40-50% risk to experience at least one symptomatic UTI episode at some time during their life. In the initial step of the infection, the lectin FimH, located at the tip of bacterial pili, interacts with the high-mannosylated uroplakin Ia glycoprotein on the urinary bladder mucosa. This interaction is critical for the ability of UPEC to colonize and invade the bladder epithelium. X-ray structures of FimH co-crystallized with two different ligands, the physiological binding epitope oligomannose-3 and the antagonist biphenyl α-D-mannoside 4a revealed different binding modes, an in-docking-mode and an out-docking-mode, respectively. To accomplish the in-docking-mode, that is the docking mode where the ligand is hosted by the so-called tyrosine gate, FimH antagonists with increased flexibility were designed and synthesized. All derivatives 5-8 showed nanomolar affinities, but only one representative, the 4-pyridiyl derivative 5j, was as potent as the reference compound n-heptyl α-D-mannoside (1b). Furthermore, a loss of affinity was observed for C-glycosides and derivatives where the triazole aglycone is directly N-linked to the anomeric center. A conformational analysis by NMR revealed that the triazolyl-methyl-C-mannosides 8 adopt an unusual (1)C(4) chair conformation, explaining the comparably lower affinity of these compounds. Furthermore, to address the druglikeness of this new class of FimH antagonists, selected pharmacokinetic parameters, which are critical for oral bioavailability (lipophilicity, solubility, and membrane permeation), were determined., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Broad modifications of various positions of the minimal natural epitope recognized by the myelin-associated glycoprotein (MAG), a blocker of regeneration of neurite injuries, produced sialosides with nanomolar affinities. However, important pharmacokinetic issues, for example, the metabolic stability of these sialosides, remain to be addressed. For this reason, the novel non-carbohydrate mimic 3 was designed and synthesized from (-)-quinic acid. For the design of 3, previously identified beneficial modifications of side chains of Neu5Ac were combined with the replacement of the ring oxygen by a methylene group and the substitution of the C(4)-OH by an acetamide. Although docking experiments to a homology model of MAG revealed that mimic 3 forms all but one of the essential hydrogen bonds identified for the earlier reported lead 2, its affinity was substantially reduced. Extensive molecular-dynamics simulation disclosed that the missing hydrogen bond of the former C(8)-OH leads to a change of the orientation of the side chain. As a consequence, an important hydrophobic contact is compromised leading to a loss of affinity., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The selectin-leukocyte interaction is the initial event in the early inflammatory cascade. This interplay proceeds via the terminal tetrasaccharide sialyl Lewis(x) (sLe(x)), present on physiological selectin ligands and E- and P-selectins located on the endothelial surface. Blocking this process is regarded as a promising therapeutic approach for inflammatory diseases where excessive leukocyte efflux is responsible for tissue damage. Selectin antagonists are generally based on sLe(x) as lead structure, containing the essential pharmacophores pre-oriented in the bioactive conformation. In this work, we describe a set of competitive sLe(x) mimetics possessing the carboxylic acid pharmacophore equipped with additional hydrophobic substituents as neuraminic acid (Neu5Ac) replacements. This small library of antagonists derived from Huisgen-1,3-dipolar cycloadditions allows to further probe the carbohydrate recognition domain of E-selectin., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

A series of novel aryl-substituted triazolyl D-galactosamine derivatives was synthesized as ligands for the carbohydrate recognition domain of the major subunit H1 (H1-CRD) of the human asialoglycoprotein receptor (ASGP-R). The compounds were biologically evaluated with a newly developed competitive binding assay, surface plasmon resonance and by a competitive NMR binding experiment. With compound 1b, a new ligand with a twofold improved affinity to the best so far known D-GalNAc was identified. This small, drug-like ligand can be used as targeting device for drug delivery to hepatocytes.

A series of novel, fluorescent ligands designed to bind with high affinity and specificity to the asialoglycoprotein receptor (ASGP-R) has been synthesized and tested on human liver cells. The compounds bear three non-reducing, beta-linked Gal or GalNAc moieties linked to flexible spacers for an optimal spatial interaction with the binding site of the ASGP-R. The final constructs were selectively endocytosed by HepG2 cells derived from parenchymal liver cells-the major human liver cell type-in a process that was visualized with the aid of fluorescence microscopy. Furthermore, the internalization was analyzed with flow cytometry, which showed the process to be receptor-mediated and selective. The compounds described in this work could serve as valuable tools for studying hepatic endocytosis, and are suited as carriers for site-specific drug delivery to the liver.

The selectins play a key role in the inflammatory process, that is, the recruitment of leukocytes from blood vessels into inflamed tissue. Because excessive infiltration of leukocytes can induce acute or chronic reactions, the control of leukocyte extravasation is of great pharmaceutical interest. All physiological ligands of the selectins contain the tetrasaccharide epitope sialyl Lewis(x), which therefore became the lead structure in selectin antagonist research. Previous studies indicated that an important factor for the affinity of sLe(x) is the fact that in solution its pharmacophores are already conformationally pre-organized in the bioactive orientation. In mimics where the GlcNAc- and the NeuNAc-moieties of sLe(x) were replaced by (R,R)-cyclohexane-1,2-diol and (S)-cyclohexyllactic acid, respectively, an optimized pre-organization of the pharmacophores could be realized, leading to antagonists with improved affinities. To further optimize the pre-organization of the carboxylic acid, a pharmacophore essential for binding, the replacement of NeuNAc by bulky (R)- and (S)-adamantyl-lactic acid was studied. Although antagonist (S)-7 showed a slightly reduced affinity, the expected beneficial effect of the (S)-configuration at C-2 of the lactate could be confirmed.

The synthesis of phenoxyphenyl, phenoxybenzyl, biphenyl, and phenyltriazole substituted sialic acid derivatives as mimics of the tri- and tetrasaccharide epitopes of GQ1balpha is described. These synthetically easily available sialosides show comparable or even enhanced affinity to MAG compared with the natural tri- and tetrasaccharide epitopes and form a new class of potential MAG antagonists.

The trisaccharide substructure 13 of the ganglioside GQ1balpha shows a remarkable affinity for the myelin-associated glycoprotein (MAG). In the search for structurally simplified and pharmacokinetically improved mimics of 13, sialosides with modifications at the reducing and non-reducing end were synthesized. The biological evaluation of mimics 12a-o was performed in a competitive target-based assay. It was found that the relative inhibitory potency (rIP) of antagonist 12h was enhanced by more than 1000-fold in comparison to the reference trisaccharide 13, despite the former having a much simpler structure. In addition, the sialic acid derivatives, for example, 12h, have clearly improved pharmacokinetic properties due to the presence of aromatic moieties, a lower molecular weight, and a reduced number of polar hydroxy functions compared to the reference compound 13.

The tetrasaccharide substructure 1 of the ganglioside GQ1balpha shows a remarkable affinity for the myelin-associated glycoprotein (MAG). In the search for structurally simplified and pharmacokinetically improved mimics of 1, biphenyl was identified as a feasible replacement for the core disaccharide Galbeta(1-3)GalNAc according to saturation transfer difference (STD) NMR and molecular modeling investigations. Using Suzuki coupling, a convergent synthesis of the mimics was achieved. To optimize the yields of the coupling reactions, the catalytic effects of microwave irradiation and conventional heating were compared. The biological evaluation of mimics 3 and 4 was performed in a competitive target-based assay. It was found that the relative inhibitory potency (rIP) of antagonist 3 was clearly enhanced in comparison to the reference trisaccharide 2, despite the former having a much simpler structure. In addition to the improved synthetic feasibility, an increase of the partition coefficient between octanol and water (logP), and therefore a beneficial change in the pharmacokinetic properties of 3 and 4 was achieved.