Synthesis and Unexpected Binding of Monofluorinated N,Nʹ-Diacetylchitobiose and LacdiNAc to Wheat Germ Agglutinin

Wheat germ agglutinin (WGA) is a carbohydrate-binding protein (lectin) abundant in the seeds of common wheat. WGA is used as a model lectin to elucidate the principles governing carbohydrate-lectin interactions. Moreover, WGA acts as a fungistatic, cytotoxic, or antiviral agent with potential in various biomedical applications. For example, WGA displayed direct affinity to SARS-CoV-2 viral particles, potentially inhibiting the viral infection in vitro. This study, published in the journal Bioorganic Chemistry, focuses on the synthesis of novel fluorinated disaccharide-based WGA inhibitors and provides a detailed investigation of their supramolecular recognition by WGA using biophysical methods and molecular modeling.

We have prepared a unique series of mono-fluorinated analogues of disaccharides N,N‘-diacetylchitobiose, and N,N‘-diacetyllactosamine (LacdiNAc). All hydroxyl groups in these parent compounds were systematically one by one replaced by fluorine, thus providing ten novel mono-fluorinated disaccharides. Subsequently, we investigated the affinity of these compounds to WGA using an enzyme-linked lectin assay (ELLA) and isothermal titration calorimetry (ITC). These methods revealed that two compounds 4′F-LacdiNAc and 6′F-N,N‘-diacetylchitobiose showed an improved binding affinity. Most strikingly, 6′F-N,N‘-diacetylchitobiose displayed an unprecedented ten-fold affinity improvement compared to parent non-fluorinated N,N‘-diacetylchitobiose. We interpreted this effect using molecular modeling and biomolecular NMR techniques, which provided insight into the mechanism of supramolecular recognition. Incorporation of fluorine at the 6′-position in N,N‘-diacetylchitobiose probably strengthened the attractive CH‒π interactions between the H6’_proR proton in the ligand and the aromatic side chains of Phe/Tyr amino acids in WGA binding sites, which increased affinity.

In summary, this work demonstrates that selective fluorination of carbohydrates can significantly improve their affinity toward their cognate proteins. Given the broad application potential of WGA, the novel inhibitors reported in this study may find biomedical applications as research tools and reference WGA ligands, taking advantage of their improved affinity and ¹⁹F NMR activity. This work was performed in the Research Group of Bioorganic Chemistry and Biomaterials under the supervision of Dr. Jindřich Karban, and in collaboration with several research institutions, including the Institute of Microbiology of the Czech Academy of Sciences, University of Chemistry and Technology in Prague, and the Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences.

• Kurfiřt M., Hamala V., Beránek J., Červenková Šťastná L., Červený J., Dračínský M., Bernášková J., Spiwok V., Bosáková Z., Bojarová P., Karban J.*: Synthesis and unexpected binding of monofluorinated N,Nʹ-diacetylchitobiose and LacdiNAc to wheat germ agglutinin. Bioorg. Chem. 2024, 147(June 2024), 107395. doi.org/10.1016/j.bioorg.2024.107395