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Receptors for Saccharides

Saccharides play key roles in important biological processes such as cell-cell differentiation and recognition and are therefore becoming important therapeutic targets [33]. Synthetic receptors designed to target carbohydrate molecules could be used to prevent viral infectivity, transport saccharides across membranes and facilitate the introduction of drugs into specific cell types. The potential applications of saccharide recognition have prompted the development of numerous synthetic receptors based mostly on macrocycle and calixarene scaffolds [34]. Foldamers that can recognize and bind saccharides could similarly have broad applications.

Prompted by the successful design of intramolecularly hydrogen bonded foldamers, Li and co-workers further developed foldamers 10, 11 and 12 (Fig. 7.8a) by introducing a series of 1,2-dibenzoyl hydrazide groups that can form three-centered H bonds [35]. The presence of an extensive network of intramolecular hydrogen bonds forces the oligomers to fold into a rigid circular or helical conformation depending on the length of the oligomer. Crystal structures of the hydra-zide building blocks confirmed the existence of the predicted hydrogen bonds and 1H NMR and NOESY experiments established the presence of a compact well-folded structure in chloroform which is stabilized by an extensive hydrogen-bonding network. According to computer models, the folded structure should po-

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