Chlorosulfonylated calix[4]arenes: precursors for neutral anion receptors with a selectivity for hydrogen sulfate

In nature phosphate and sulfate binding proteins are very important receptors for the active transport systems in the cell.^1-2 A very high selectivity in binding has been observed in prokaryotic, periplasmic phosphate and sulfate binding proteins, which demonstrate >10® selectivity for binding phosphate over sulfate and sulfate over phosphate, respectively.³ In both proteins the specific binding
exclusively takes place through hydrogen bonding.
Synthetic receptors that bind anions contain either positively charged guanidinium or ammonium groups⁴ or Lewis acid metal centers⁵ to accomplish anion binding. Recently we reported functionalized uranyl-containing salenes⁶ and sulfonamides⁷ derived from tris(aminoethyl)-amine (TREN) that form complexes with hard anions in CH₃CN with a selectivity for H₂PO₄™. In the present paper we report anion receptors based on chlorosulfonylated
calix[4] arenes.⁸
Calix[4]arenes are important building blocks in supramolecular chemistry.^10-11 They can be (selectively) functionalized both at the phenolic OH groups (lower rim) and at the para positions of the phenol rings (upper rim).¹²