| Abstract: | The decapeptide pBrBz- (Aib)10-OtBu, 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 310-helical structure stabilized by eight N? H …? O?C intramolecular 1 ← 4 (or C10) 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 1H-nmr study in solution. |
