Syntheses and ion selectivities of tri-amide derivatives of hexahomotrioxacalix[3]arene. Remarkably large metal template effect on the ratio of cone vs. Partial-cone conformers

We have found that a homotrioxacalix[3]arene (1H₃) -based ionophore with a cone conformation, which is very difficult to obtain by the reaction of 1H₃ and ethyl bromoacetate, can be synthesized quantitatively by the reaction of 1H₃ and N,N-diethylchloroacetamide in THF in the presence of NaH. The conformer distribution of the tri-amide derivative (1Am₃) between cone and partial-cone was sensitively affected in 0 ∼ 100% range by the metal template effects. Cone-1Am₃ showed the very high affinity for alkali and alkaline earth metal cations. Particularly, it formed stable complexes with alkaline earth metal cations which were scarcely bound to the tri-ester derivative. The results show that cone-1Am₃ acts as an excellent neutral ionophore owing to the three coordinative amide groups arranged in C₃-symmetry.