1,8-Naphthyridine Based Artificial Receptors for Selective Monosaccharide Binding in Water

1,8-Naphthyridine based bi-bracchial macrocyclic 2 and cage-type macrobicyclic receptor 3 bind monosaccharides in water under physiologically relevant conditions through a combination of hydrophobic, electrostatic and hydrogen bonding interactions. The dissociation constants (K-d) for the complexes between 1,8-naphthyridine receptors 1-3 with a variety of neutral and negatively charged monosaccharides in water were determined by fluorimetric and UV/vis titration. The observed values are in the range from similar to 0.3 to >= 10 mM, and are similar to the K-d reported for lectin/monosaccharide complexes. Among the monosaccharide substrates tested, receptor 2 showed the strongest binding affinity for sialic acid (K-d = similar to 0.3 mM), a monosaccharide that plays many important roles in a wide variety of physiological and pathological processes. Interestingly, receptors 2 and 3 display the ability to discriminate between closely related monosaccharide substrates by opposite variation of the fluorescence emission intensity.