Conformation of sequential peptides containing proline residues

Abstract

The conformational properties of Boc‐Leu3‐(Pro2GlyLeu3)n‐Pro2Gly‐OH(n = 0, 1, 3, and 5) and Boc‐Leu3‐(Pro2GlyLeu3)n‐Pro2Gly‐OBzl (n = 7, 9, and 11) were investigated in various organic solvents of high polarity using molar rotation and CD measurements. The peptides examined are assembled by the N‐terminal, internal, and C‐terminal segments having the sequences of Boc‐Leu3, Pro2Gly‐Leu3, and Pro2Gly‐OX (X = H or Bzl), respectively. The conformational studies using the molar rotation of the oligopeptides and polypeptides in MeOH, DMSO, DMF, DMA, and NMP have made it clear that all the peptides have a randomly coiled structure. CD spectral patterns of the peptides in MeOH were essentially the same as each other and indicative of the randomly coiled structure. The additive nature of the total molar rotation and total molar ellipticity in Boc‐Leu3‐(Pro2GlyLeu3)n‐Pro2Gly‐OX (X = H or Bzl) indicates that the “peptide segment separation” is indeed in operation in organic solvents of high polarity and that the peptide molecule can be considered to be assembled with the small peptide segments having a randomly coiled structure.