Preferred conformation of peptides rich in alicyclic C-alpha,alpha-disubstituted glycines

The conformational preferences of the alicyclic C-alpha,C-alpha-distributed glycines Ac(n)c (1-amino-1-cycloalkane-carboxylic acid; n = 4, 7, 9, 12) were assessed in selected model compounds, including homopeptides and Ala (or Aib, alpha-aminoisobutyric acid)/Ac(n)c peptides containing a small total number of residues, by Fourier transform ir absorption, H-1-nmr, and x-ray diffraction analyses. The results obtained indicate that beta-turn and 3(10)-helical structures are preferentially adopted by short peptides rich in these cycloaliphatic alpha-amino acids.