We describe the synthesis of unprecedented calixpyrrole receptors featuring “super aryl extended” (SAE) cavities. We elaborated the aromatic cavity provided by the αααα-isomer of para-tetraiodo-meso-phenyl calixpyrrole by installing ethynyl-aryl substituents at its upper rim. We report the binding properties of the prepared SAE-calixpyrrole tetraester towards pyridyl-N-oxides. The binding data revealed the formation of thermodynamically and kinetically highly stable 1:1 complexes. The complexation-induced chemical shifts indicated the formation of hydrogen bonds and aromatic interactions with the calix-core adopting the cone conformation. We quantified the additional interactions established between the four terminal aryl groups and the para-phenyl substituent of 4-phenyl pyridine N-oxide to be in the order of 1 kcal mol−1. The complex formation rate was found to be close to the diffusion control suggesting that the free host adopted a 1,3-alternate conformation. Finally, we attempted to gain water solubility of SAE-calixpyrroles using derivatives that display four ionizable or charged groups at their upper rims.
Super Aryl-Extended Calixpyrroles: Synthesis, Binding Studies, and Attempts To Gain Water Solubility
Chemistry - A European Journal 2016, 22 (38), 13682-13689.