Fluorinated Carbohydrates as Lectin Ligands: Synthesis of OH/F-Substituted N-Glycan Core Trimannoside and Epitope Mapping by 2D STD-TOCSYreF NMR spectroscopy.

Glycan-protein interactions play an important role in a broad range of physiological processes, raising interest to elucidate the structural interplay. Yet, their dynamic nature limits the analysis by crystallography, whereas NMR spectroscopy suffers from the low H dispersion of glycans. Therefore, their sparse fluorination and NMR screening by 1D Saturation Transfer Difference with relay to F (STDreF) was previously proposed to exploit the superior dispersion in F NMR spectroscopy. A new 2D STD-TOCSYreF experiment is presented here that enables comprehensive epitope mapping of fluorinated glycans by combining the spectral resolution of F with the spatial resolution and coverage of H. For an illustration, the 2-deoxy-2-fluoro derivative of the N-glycan core trimannoside was synthesised and its recognition of Pisum sativum agglutinin by either of the two terminal mannose residues was confirmed. Going beyond the crystallographic information, the 2D STD-TOCSYreF spectrum moreover visualised collateral contacts from the branching mannose and allowed to assess the ratio of both co-existing binding modes through the α1,3- (67 %) and α1,6-linked (33 %) terminal mannose moieties.