Neutral anion receptors with multiple urea-binding sites

The synthesis of macrocyclic and acyclic cleft-like anion receptors in whic h four hydrogen bond donating urea moieties are present in a preorganized f ashion is described. NMR spectroscopy shows the complex formation with H2PO 4- and Cl-. Cleft-like receptors bind H2PO4- in a 2:1 guest-host stoichiome try (K-a = 10(7) M-2) in DMSO, whereas Cl- is bound in a 1:1 stoichiometry (K-a = 10(3)M(-1)). The macrocyclic receptors form a 1:1 complex with H2PO4 - (K-a = 10(3) M-1 in DMSO) with a 100-fold selectivity for H2PO4- over Cl- .