Polymethylene-bridged Cystine–Glycine-containing Cyclopeptides as Hydrogen-bonding Electroneutral Anion Receptors: Design, Synthesis, and Halide Ion Recognition

Two conformationally constrained polymethylene-bridged cystine–glycine-based cyclopeptides (3 and 5) were synthesized as hydrogen-bonding electroneutral anion receptors by the conventional solution method. Both solution conformation and NMR titration studies showed that cyclopeptide 3 was an efficient receptor for selective recognition of halide ions, whereas cyclopeptide 5 failed to bind any halide ion.