Linear oligopeptides. XLIII. Study of the relationship between conformation and nature of side chain: Homologous series derived from γ-branched amino acid residues

Conformational studies of the three homologous series, from dimer through heptamer, of monodisperse, N‐and C‐protected oligopeptides derived from the γ‐branched α‐amino acid residues L‐leucine, β‐cyclohexyl‐L‐alanine, and L‐phenylalanine are reported. By means of ir absorption and CD in the vacuum‐uv (150nm), the occurrence of intermolecular β‐conformations in the higher oligomers in the solid state was established. In solvents of low polarity at high dilution, the extent of intramolecularly hydrogen‐bonded folded‐structure formation was assessed as a function of chain length and the nature of the side chain. Unordered and intermolecular β‐conformations were found in alcohols and aqueous alcoholic mixtures. The results obtained indicate that—the position of branching being equal–steric requirements, electronic properties, and hydrophobic character of the amino acid side chains are all important in determining the nature and stability of oligopeptide conformations. Copyright © 1978 John Wiley & Sons, Inc.