Carbohydrate recognition through H-bonding and CH-π interactions by porphyrin-based receptors

Porphyrin-based synthetic receptors containing urea, carbamate, or amide groups were designed and synthesized for carbohydrate recognition. The receptors have equatorially and convergently directed hydrogen-bonding sites into which the urea, carbamate, or amide groups were introduced above the porphyrin plane. The receptors exhibited remarkable affinities to pyranoside/furanoside derivatives in organic media, demonstrating not only the importance of multiple hydrogen-bonding interactions but also CH-π interactions in carbohydrate recognition. Among the three hydrogen-bonding groups, urea NHs were used as the strongest H-bonding donors for sugar hydroxyl oxygens, and the porphyrin plane was used for mimicking CH-π interactions with sugar CHs, which are found in sugar-binding proteins. The binding interactions between the artificial receptors and carbohydrates were elucidated by various spectroscopic analyses such as UV-vis titration, (1)H NMR titration, CD measurement, and computer-assisted modeling.