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Abstract

β‐Peptides are an interesting new class of transmembrane model peptides based on their conformationally stable and well‐defined secondary structures. Herein, we present the synthesis of the paramagnetic β‐amino acid β3‐hTOPP (4‐(3,3,5,5‐tetramethyl‐2,6‐dioxo‐4‐oxylpiperazin‐1‐yl)‐d‐β3‐homophenylglycine) that enables investigations of β‐peptides by EPR spectroscopy. This amino acid adds to the so far sparse number of β‐peptide spin labels. Its performance was evaluated by investigating the helical turn of a 314‐helical transmembrane model β‐peptide. Nanometer distances between two incorporated β3‐hTOPP labels in different environments were measured using PELDOR/DEER (pulsed electron‐electron double resonance) spectroscopy. Due to the semi‐rigid conformational design, the label delivers reliable distances and sharp (one‐peak) distance distributions even in the lipid bilayer. The results indicate that the investigated β‐peptide folds into a 3.2514 helix and maintains this conformation in the lipid bilayer.