Molecular Recognition of N-Acetylneuraminic Acid by Acyclic Pyridinium- and Quinolinium-Based Receptors in Aqueous Media: Recognition through Combination of Cationic and Neutral Recognition Sites

Compounds 5b-8b and 10b, and 11b, containing a triethylbenzene scaffold substituted with both neutral and cationic recognition sites, were shown to be effective receptors for N-acetylneuraminic acid (NeuAc), the most common occurring sialic acid, in highly competitive solvents. These compounds were established to be more powerful receptors for NeuAc than the symmetrical pyridinium- and quinolinium-based compounds 9b and 12b in aqueous media. As in natural protein-sialic acid complexes, the combination of neutral/charge-reinforced hydrogen bonds, ion pairs, CH-pi, and van der Waals interactions seems to be responsible for the effective binding of this naturally widespread anionic carbohydrate in aqueous media.