Conformations of Peptides Containing a,a-Dialkylated Residues with Linear and

The conformational properties of a,a-dialkylated amino acid residues possessing acyclic (diethylglycine, Deg; ’ di-n-propylglycine, Dpg; di-n-butylglycine, Dbg) and cyclic (l-amino-cycloalkane-1-carboxylic acid, Acnc) side chains have been compared in solution. Thejive pep-tides studied by nmr and CD spectroscopy are Boc-Ala-Xxx-Ala-OMe, whereXxx = Deg ( I), Dpg (II), Dbg ( H I) , Ac6c (IV), and A c, ~ (V) . Delineation of solvent-shielded NH groups have been achieved by solvent and temperature dependence of NH chemical shijis in CDC13 and (CD3),S0 and by paramagnetic radical induced line broadening in peptide III. In the Dx