Fluoroacetamide Moieties as NMR Spectroscopy Probes for the Molecular Recognition of GlcNAc-Containing Sugars: Modulation of the CH-π Stacking Interactions by Different Fluorination Patterns.

We herein propose the use of fluoroacetamide and difluoroacetamide moieties as sensitive tags for the detection of sugar-protein interactions by simple1 H and/or19 F NMR spectroscopy methods. In this process, we have chosen the binding of N,N'-diacetyl chitobiose, a ubiquitous disaccharide fragment in glycoproteins, by wheat-germ agglutinin (WGA), a model lectin. By using saturation-transfer difference (STD)-NMR spectroscopy, we experimentally demonstrate that, under solution conditions, the molecule that contained the CHF2 CONH- moiety is the stronger aromatic binder, followed by the analogue with the CH2 FCONH- group and the natural molecule (with the CH3 CONH- fragment). In contrast, the molecule with the CF3 CONH- isoster displayed the weakest intermolecular interaction (one order of magnitude weaker). Because sugar-aromatic CH-π interactions are at the origin of these observations, these results further contribute to the characterization and exploration of these forces and offer an opportunity to use them to unravel complex recognition processes.