Looking for a Robust, Synthetic, Fully‐Extended (2.0 5 ‐Helical) Peptide Structure – Effect of Terminal Groups

The incorporation of α‐amino acids with a quaternary α‐carbon atom into a peptide provides a tool to effectively restrict the available range of its backbone conformations. Specifically, under favorable conditions, C α,α ‐diethylglycine (Deg) homopeptides are known to preferentially adopt the fully‐extended (2.0 5 ‐helical) structure, which is characterized by the longest possible separation between two adjacent α‐amino acid C α atoms. We have investigated the influence of the nature of the N‐ and/or C‐terminal protecting (or blocking) groups on the relative stabilities of the fully‐extended conformation vs. the competing, shorter 3 10 ‐helical structure in a synthetic Deg homopeptide series.