Anion Recognition by Neutral Macrocyclic Azole Amides

A straightforward synthesis of C-2-symmetric azole-containing macrocyclic peptides is presented. This type of macrocycle possesses four amide groups directed into the interior of the scaffold that act as hydrogen-bond donors and two nitrogen atoms from the azole unit that act as hydrogen-bond acceptors. This arrangement makes them sensitive receptors for Y-shaped anions like AcO- and H2PO4- with a selectivity for dibydrogen phosphate versus acetate, as was shown with H-1 NMR titration techniques in [D-6]DMSO/5% CDCl3. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)