STRUCTURES OF POLYPEPTIDES FROM ALPHA-AMINO-ACIDS DISUBSTITUTED AT THE ALPHA-CARBON

The structural preferences of homopeptides from Aib, Deg, Dpg, and Ac(n)c (n = 3, 5, and 6) residues, as determined by conformational energy computations, X-ray diffraction analyses, and spectroscopic studies,are reviewed. There results obtained indicate that the 3(10)-helix and the fully extended (C5) conformation are preferentially adopted by long sequences of these C-alpha,alpha-disubstituted alpha-amino acid residues, depending upon bulkiness and nature (whether linear or cyclic) of their side chains.