Carboxylate-Based Receptors for the Recognition of Carbohydrates in Organic and Aqueous Media

Acyclic receptors containing neutral and ionic hydrogen-bonding sites, such as amino-pyridine and
carboxylate groups, were prepared and their binding properties toward neutral sugar molecules were
studied. The binding studies with disodium and bis(tetramethylammonium) salts containing the dianion
11 have revealed that this type of receptor molecule is able to recognize the selected sugars in both
organic and aqueous media. The carboxylate/pyridine-based receptor 11 exhibits in chloroform at least
a 100-fold higher affinity for glucopyranosides than the previously described triarmed pyridine-based
receptor 1, incorporating only neutral hydrogen-bonding sites. A substantial drop in the association
constants is expectedly observed for an ester analogue of 11, compound 9. The dicarboxylate 11 is able
to form complexes in water with methyl β-d-glucopyranoside and d-cellobiose, with a preference for the
disaccharide. The studies show the importance of charge-reinforced hydrogen bonds in the recognition
of carbohydrates.