Description:
<jats:title>Abstract</jats:title><jats:p>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 β<jats:sup>3</jats:sup>‐hTOPP (4‐(3,3,5,5‐tetramethyl‐2,6‐dioxo‐4‐oxylpiperazin‐1‐yl)‐<jats:sc>d</jats:sc>‐β<jats:sup>3</jats:sup>‐homophenylglycine) that enables investigations of β‐peptides by EPR spectroscopy. This amino acid adds to the, to date, sparse number of β‐peptide spin labels. Its performance was evaluated by investigating the helical turn of a 3<jats:sub>14</jats:sub>‐helical transmembrane model β‐peptide. Nanometer distances between two incorporated β<jats:sup>3</jats:sup>‐hTOPP labels in different environments were measured by using pulsed electron/electron double resonance (PELDOR/DEER) 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 3.25<jats:sub>14</jats:sub> helix and maintains this conformation in the lipid bilayer.</jats:p>