A Simple Strategy to Obtain Synthetic Ca²⁺-Dependent Lectin Mimics

Many lectins require a Ca²⁺ ion as structure directing co-factor to function as carbohydrate binders. Such lectins are implicated in various important biological processes such as inflammation and infection, yet a simple strategy to mimic their function is lacking. Herein, a very simple dipyridyl ligand (6) is reported that can organize around a Pd²⁺ ion to form the ring-like complexes [PdCl₂6] and [Pd6₂]²⁺. In CD₂Cl₂ with 5 % dmos-d⁶, ligand 6 does not associate with glycosides, while its Pd²⁺ complexes selectively bind to β-n-octyl-glycosides over α-n-octyl-glycosides. The highest affinity (K-^a1:1 ≈ 116 M^-1) was found between the dicationic [Pd6₂]²⁺ and n-octyl-β-D-galactoside. Molecular modelling suggests a common binding motif with an important role of C-H...π interactions and two charge assisted bifurcated [N-H/C-H]⁺...O hydrogen bonds. Ligand 6 and its metal complexes thus provide a proof-of-concept for a very simple strategy to mimicking Ca²⁺-dependent lectins.