Highly Selective Recognition of alpha-Chiral Primary Organoammonium Ions by C-3-Symmetric Peptide Receptors

A straightforward synthesis of C-3-symmetric, imidazole-containing, macrocyclic peptides with different binding arms is presented. The chirality of the backbone and the selection of adequate receptor arms make these systems highly selective receptors for a-chiral primary organoamnionium ions. Furthermore, the receptors have the ability to discriminate between enantiomeric guests with selectivity ratios of up to 87:13. The binding constants and the selectivity ratios were estimated by standard H-1 NMR titration techniques in CDCl3. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)