Linear oligopeptides, 77. The effect of the insertion of a proline residue on the solid‐state conformation of host peptides

The conformational properties of two series of monodispersed, chemically and optically pure, PEG The following abbreviations have been used in the text: PEG, poly(ethylene glycol); ‐NHPEG, “amino‐PEG”; ‐NHPEG‐M, “amino‐PEG” monomethyl ether; NPS, o‐nitrophenylsulfenyl; t‐Boc, tert‐butoxycarbonyl; Z, benzyloxycarbonyl; Met, methionine; Pro, proline; OBzl, benzyloxy; OMe, methoxy; OEt, ethoxy; NHEt, ethylamino; Glu, glutamic acid; IR, infrared; MeOH, methanol; TFE, 2,2,2‐trifluoroethanol. ‐bound linear host oligopeptides of the general formula {article}{empty}{document}t - Boc-- (L - Met-- )ₙ NHPEG{document} and {article}{empty}{document}t - Boc-- [L - Glu(OBl)-- ]ₙ NHPEG - M{document} containing a single guest L‐Pro residue at different positions in the main chain have been investigated in the solid state using IR absorption. The corresponding N‐deblocked peptides have also been examined. The incorporation of a L‐Pro residue in a central position of a β‐conformation appears to induce the onset of a structural irregularity characterized by IR absorption bands in the vicinity of 3 325 cm−1 and 1 575 cm−1.