The Easy Disruption of the β-Sheet Structure of Resin-Bound Human Proinsulin C-Peptide Fragments by Strong Electron-Donor Solvents

Abstract

Abstract The β-sheet structure disruption of cross-linked polystyrene resin-bound human proinsulin C-peptide fragments containing Pro residues at suitable intervals was investigated by a solvent titration method in CH2Cl2, mainly using TFE and HMPA as titrating solvents. The easy disruption of the β-sheet structure of resin-bound peptides in CH2Cl2 by TFE and HMPA strongly suggested that the concept of “the peptide segment separation by tertiary peptide bonds” was useful for estimating the β-sheet-structure-disrupted behavior and that the β-sheet structure of the protected peptides having high 〈Pc〉 values could easily be disrupted in a medium electron-acceptor solvent of CH2Cl2 by the addition of a strong electron-donor solvent of HMPA in spite of the electron donor-acceptor interaction between solvents. The present results indicate that effective solvents for solid-phase peptide synthesis by a fragment condensation procedure should be searched by taking the average helix, β-sheet, and coil conformation values, 〈Pα〉, 〈Pβ〉, and 〈Pc〉, of peptide segments into consideration.