Enhancing lectin recognition via precise fluorination: Man5 glycomimetics for targeting DC-SIGN.

High-mannose N-glycans, particularly Man9GlcNAc2, are key DC-SIGN ligands but remain synthetically challenging, motivating the development of accessible glycomimetics capable of reproducing lectin recognition. Here, we report a precise fluorination strategy to enhance DC-SIGN recognition using Man5-based glycomimetics. Four fluorinated Man5 derivatives were synthesized with selective substitution at C-2 and/or C-6 of terminal mannoses, preserving Ca2+ coordination. Biophysical evaluation revealed a strong positional dependence: C-6 fluorination markedly increased affinity, whereas C-2 substitution reduced binding. The (6F,6F)-Man5 derivative 1 exhibited the highest inhibitory potency, surpassing the natural Man5 and slightly exceeding the Man9 epitope in blocking DC-SIGN binding to the SARS-CoV-2 spike protein. NMR binding epitope mapping and MD simulations confirmed preferential engagement of the α(1→3) branch and fluorine-dependent stabilization of local contacts. ITC studies indicated that enhanced binding arises from favorable enthalpic contributions, supported by both polar interactions and fluorination-driven desolvation. These results establish selective fluorination as a powerful strategy to boost lectin ligands affinity and generate potent glycomimetics for targeting DC-SIGN.