Preferred conformation of the terminally blocked (Aib)₁₀ homo‐oligopeptide: A long, regular 3₁₀‐helix

Abstract

Abstract The decapeptide p BrBz‐ (Aib) 10 ‐O t Bu, synthesized by the 5( 4H )‐oxazolone method, crystallizes in the monoclinic space group C2/c with a = 43.901(2), b = 9.289(2), and c = 34.746(3) A; β = 114.69(3)°; and Z = 8. The crystals contain one molecule of water associated with each peptide. The structure has been solved by the Patterson method and refined to an R value of 0.073 for 6819 observed reflections. The peptide adopts a regular 3 10 ‐helical structure stabilized by eight NH …︁ OC intramolecular 1 ← 4 (or C 10 ) H bonds. This study has allowed us to characterize this important peptide secondary structure in great detail. The crystal‐state conformation agrees well with proposals made on the basis of an ir absorption and 1 H‐nmr study in solution.