The macrotricyclic system as a receptor for carbohydrates in organic as well as aqueous media has been extensively studied within the Davis group. The hydrogen bonding and CH-π interactions are the two main non covalent interactions operating for the recognition of carbohydrates in our system. In principle higher affinities could be achieved by enhancing either of these types of interactions. The possibility of enhancing H-bonding interactions with host-guest was explored by the introduction of heterocyclic linkers in the 'temple' receptors. Macrocycle with pyrrole linker 132 and pyridine linker 131 (Figure i) were synthesised and studied for their affinities with different carbohydrate substrates. Pyrrole macrotricycle 132 bound D- Glucose selectively over other substrates with K; = 18 M-1. However pyridine macrotricycle 131 did not show selectivity and higher affinities with any substrates. Figure i. Macrotricycle with pyridine linker 131 and pyrrole linker 132. In collaboration with Roelens group in Firenze, Italy, a series of water soluble C3-symmetric receptors were synthesized and studied for their affinity for carbohydrates. Unfortunately, these series of receptors did not bind the substrates strong enough to be detected by lH NMR titration studies.
