New macrobicyclic receptors for amino acids

Two new receptors, 9 and 13, have been prepared, utilising a pyridyl aryl ether unit in the rim of the macrobicyclic structure, and the crystal structures for both of these receptors are reported. The presence of the pyridyl unit provides additional hydrogen bonding functionality in comparison to earlier structures of this type, and 9 is an effective receptor for N-acetyl l-asparagine carboxylate in CH2Cl2.