Linear oligopeptides, 55. Infrared conformational analysis of polyethyleneglycol‐bound alanine and valine homo‐L‐oligopeptides in the solid state and in solution

Abstract

AbstractThe IR absorption properties of three series of monodisperse, chemically and optically pure, PEG‐bound linear homo‐oligopeptides having the general formula t‐Boc‐(L‐Ala‐)1–8Gly‐OPEG, t‐Boc‐(L‐Val‐)1–7Gly‐OPEG and t‐Boc‐(L‐Val‐)2–8Gly‐OPEG‐M were investigated in the solid state and in solution. In the latter case the study was extended to solvents of largely different polarity and different concentrations. In the solid state the Ala and Val peptides from n = 5 to n = 8 assume essentially a β‐structure. The occurrence of the unusual parallel‐chain β‐conformation was suggested for the N‐deblocked Val highest peptides. The conformational analysis in deuterochloroform at high dilution showed that a much higher content of intramolecularly H‐bonded forms exist in Ala4 than in the Val4 peptides. At higher concentrations chain length, solvent, and side chain effects are all operative in determining the extent of peptide association. The influence of the bi‐ and monofunctional polymeric supports on the conformational properties of the Ala and Val homo‐oligopeptide series is also discussed. Finally, preliminary results on the relationship between reactivity of the polymer‐bound growing peptide chain during the step‐by‐step synthesis and peptide conformation are reported.