Squaramido-based receptors: Design, synthesis, and application to the recognition of tetraalkylammonium compounds

A new series of tripodal receptors based on squaramido rings as unprecedented binding units has been devised. Among the different structural possibilities that this functionality offers, the ability of establishing multiple O to C-H interactions has been explored. On this basis, new receptors capable of recognizing choline, acetylcholine, and related ammonium salts have been synthesized. Association constants in the range 10(3)-10(4) M(-1) have been measured by a H-1-NMR titration method The formation of intracavity complexes is supported by the observation of characteristic changes in the NMR spectra of the complexes, of intermolecular cross peaks in 2D. ROESY experiments, and by detection of signals corresponding to the molecular weight of the complexes by positive FAB mass spectrometry.