PREFERRED CONFORMATION OF PEPTIDES RICH IN ALICYCLIC C-ALPHA,C-ALPHA-DISUBSTITUTED GLYCINES

The conformational preferences of the alicyclic C-alpha,C-alpha-distri buted glycines Ac(n)c (1-amino-1-cycloalkane-carboxylic acid; n = 4, 7 , 9, 12) were assessed in selected model compounds, including homopept ides and Ala (or Aib, alpha-aminoisobutyric acid)/Ac(n)c peptides cont aining a small total number of residues, by Fourier transform ir absor ption, H-1-nmr, and x-ray diffraction analyses. The results obtained i ndicate that beta-turn and 3(10)-helical structures are preferentially adopted by short peptides rich in these cycloaliphatic alpha-amino ac ids. (C) 1997 John Wiley & Sons, Inc.