Stereoselective Synthesis of Fluorinated Galactopyranosides as Potential Molecular Probes for Galactophilic Proteins: Assessment of Monofluorogalactoside–LecA Interactions

Abstract

The replacement of hydroxyl groups by fluorine atoms on hexopyranoside scaffolds may allow access to invaluable tools for studying various biochemical processes. As part of ongoing activities toward the preparation of fluorinated carbohydrates, a systematic investigation involving the synthesis and biological evaluation of a series of mono‐ and polyfluorinated galactopyranosides is described. Various monofluorogalactopyranosides, a trifluorinated, and a tetrafluorinated galactopyranoside have been prepared using a Chiron approach. Given the scarcity of these compounds in the literature, in addition to their synthesis, their biological profiles were evaluated. Firstly, the fluorinated compounds were investigated as antiproliferative agents using normal human and mouse cells in comparison with cancerous cells. Most of the fluorinated compounds showed no antiproliferative activity. Secondly, these carbohydrate probes were used as potential inhibitors of galactophilic lectins. The first transverse relaxation‐optimized spectroscopy (TROSY) NMR experiments were performed on these interactions, examining chemical shift perturbations of the backbone resonances of LecA, a virulence factor from Pseudomonas aeruginosa. Moreover, taking advantage of the fluorine atom, the 19F NMR resonances of the monofluorogalactopyranosides were directly monitored in the presence and absence of LecA to assess ligand binding. Lastly, these results were corroborated with the binding potencies of the monofluorinated galactopyranoside derivatives by isothermal titration calorimetry experiments. Analogues with fluorine atoms at C‐3 and C‐4 showed weaker affinities with LecA as compared to those with the fluorine atom at C‐2 or C‐6. This research has focused on the chemical synthesis of “drug‐like” low‐molecular‐weight inhibitors that circumvent drawbacks typically associated with natural oligosaccharides.

Unraveling Sugar Binding Modes to DC-SIGN by Employing Fluorinated Carbohydrates

“…Thus, the interaction of tetrameric full-length DC-SIGN with the monosaccharide library was evaluated by computing the decrease of the T 2 values of the fluorinated molecules (Figure 3) in the presence of a given amount of the lectin, normalized for each peak with respect to its T 2,free [8]:% T2,decrease=T2,free−T2,obsT2,free×100 In particular, controlled amounts of DC-SIGN concentrations were added to the fluorinated sugar library and the observed T 2 values were deduced. The analysis of the data permitted deducing a systematic reduction of the signal intensities in specific cases (Figure 4), which were correlated with the presence of binding.…”

“…Ligand-based NMR experiments are widely used to study the interactions between carbohydrates and receptors in solution [1,2,3,4]. Among these methods that are especially powerful for screening purposes, 19 F-based approaches present a number of important advantages [5,6,7,8]. In this study, we applied a strategy that allows the screening of a library of synthetic fluorinated monosaccharides to study the interactions with the biologically relevant lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) [9] and, at the same time, obtain ligand-specific chemical mapping information.…”

Exploring the Chemistry of Non‐sticky Sugars: Synthesis of Polyfluorinated Carbohydrate Analogues of d‐Allopyranose

“…Moreover, we were the first group to access a 2,3,4,6‐tetradeoxy‐2,3,4,6‐tetrafluorohexopyranoside, represented by molecule 3 . Analogues of the latter compound display weak antiproliferative activity with no selectivity towards normal and cancer cell lines . Recently, the group of Linclau reported the synthesis of trifluoroglucose 2 also by using a Chiron approach .…”

“…[8] The flexibility of this strategy allowed us to also achieve the preparation of 2,3,4-trideoxy-2,3,4-trifluoro mannose,t alose, fucose,a llose, and galacturonic acid methyl ester.M oreover, we were the first group to access a2 ,3,4,6-tetradeoxy-2,3,4,6-tetrafluorohexopyranoside, represented by molecule 3.A nalogues of the latter compound display weak antiproliferativea ctivity with no selectivity towards normal and cancer cell lines. [9] Recently,t he group of Linclau reported the synthesis of trifluoroglucose 2 also by using aC hiron approach. [10] The group of Linclaua lso prepared at etrafluoroethylene-containing monosaccharide 4, which gained affinity to UDP-galactopyranose mutase from Mycobacterium tuberculosis as compared to unmodified analogues.…”

Synthesis of vicinal dideoxy-difluorinated galactoses

“…Its b-thionaphthyl glycoside displayed weak (IC50 34-38 µM) antiproliferative activity against a panel of cancer cell lines. 17 Our group has synthesised vicinal tetrafluorinated sugar derivativatives including 2,3-dideoxy-2,2,3,3-tetrafluoro-Dthreo-hexopyranose 8, 18,19 and showed that its furanosyl-UDP derivative 9 was a superior binder to UGM (galactose mutase) than the native Galp-UDP and Galf-UDP substrates. 20,21 Examples of vicinally dideoxy-difluorinated sugar derivatives include the 3,4-dideoxy-3,4-difluoro-D-glucopyranose 10 22 and its -N-acetyl glucosamine analogue 11, 23 as well as the N-acetylgalactosamine 12 23 and 2,3-dideoxy-2,3-difluoro-Dglucopyranose 13.…”