Cyclohexylether delta-Amino Acids: New Leads for Selectivity Filters in Ion Channels Financial support by the Fonds der Chemischen Industrie (FCI), the Volkswagen Foundation, the Pinguin Foundation, and Schering AG is gratefully acknowledged. H.-D.A. thanks the FCI for a PhD fellowship. We thank Dr. B. Ziemer (Humboldt-Universität zu Berlin) for the X-ray structure analysis and Dr. P. Franke (Freie Universität Berlin) for MALDI-TOF mass spectra.