Conformational analysis of polyoxyethylene‐bound homo‐oligo‐L‐glutamates in aqueous environment

Abstract

AbstractA detailed conformational analysis of homo‐oligo‐L‐glutamates was carried out in aqueous solution using 1H‐nmr spectroscopy. Three series of side‐chain protected (α‐OMe) glutamate oligopeptides, attached to polyoxyethylene (POE) to enhance their solubility, were synthesized. The effect of the N‐terminal blocking groups—Boc, Ac, and pGlu—on the conformations of these peptides in water is discussed. Unequivocal assignments were obtained for all amide NH resonances through use of selectively α‐deuterated oligo‐glutamates. Analysis of vicinal coupling constants, temperature dependence of NH chemical shifts, transfer of saturation experiments, and titration studies with a denaturing solvent (DMSO) were used to investigate the peptide structure. These data suggest that the Glu1 and Glu2 NH protons of each heptamer are solvent exposed, while the NH protons of interior glutamate residues chain are solvent sequestered. The nmr data are consistent with the onset of helical structure at the heptamer of each series in aqueous solution. The POE‐peptides with pGlu at the N‐terminus showed considerably reduced stability of structure than those with the Boc or acetyl blocking groups. Peptide conformations and their stability in water are compared to those in other solvents.