Looking for a robust, synthetic, fully-extended [2.0(5)-helical peptide structure - effect of terminal groups

The incorporation of alpha-amino acids with a quaternary alpha-carbon atom into a peptide provides a tool to effectively restrict the available range of its backbone conformations. Specifically, under favorable conditions, C-alpha,alpha-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 alpha- amino acid C-alpha 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.