The reaction of 7,15,23-tri-tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomc-3,11,19-trioxacalix-arene (1H3) with ethyl bromoacetate yielded the cone conformer (cone-1Es3) as a minor product and the partial-cone conformer (partial-cone-1 Es3) as a major product. Interconversion between these two conformers did not take place, indicating that the OCH2CO2Et group is bulky enough to inhibit the oxygen-through-the-annulus rotation. The conformer distribution was affected by the metal cation present in the base, suggesting the importance of the metal template effect. When NaH was used in THF, the partial-cone/cone ratio was 1.6–3.8; when CS2CO3 was used in acetone, partial-cone-1Es3 was produced quantitatively. Two-phase solvent extraction established that cone-1Es3 shows Na+ selectivity, whereas partial-cone-1Es3 shows K+ selectivity. Cone-1Es3 showed high affinity toward RNH3+ cations, indicating that the structure of cone-1Es3 with C3 symmetry is very suitable for the binding of RNH3+ cations with C3 symmetry. 1H NMR studies established that the phenyl units in cone-1Es3 are more or less flattened but stand up when a cationic guest is included. This paper thus demonstrates that IH3 is useful as a basic skeleton for the design of new ionophores, particularly those suitable for the recognition of guests with C3 symmetry.
All Science Journal Classification (ASJC) codes
- Organic Chemistry