¹H‐nmr studies of polyoxyethylene‐bound homo‐oligo‐L‐methionines

Abstract

SynopsisThe use of 'H-nmr spectroscopy is demonstrated to be a useful analytical method to characterize the structure of synthetic peptides attached to soluble, macromolecular polyoxyethylene (POE) supports in the liquid-phase method (LPM) of peptide synthesis. We report an extensive 360-MHz lH-nmr study of POE-bound homo-oligo-L-methionine peptides.A combination of high field and selective saturation or Redfield pulse methods allows resolution of individual backbone NH and a-CH resonances of dilute peptides in the presence of strong resonances from macromolecular POE and/or protonated solvents. The nmr spectra for the POE-bound peptides in CDC13 are qualitatively similar to those of the low-molecular-weight Boc-L-Met,-OMe peptide esters. This corroborates other observations that POE has little effect on peptide structure. The backbone a-CH region of peptides is overlapped by signals from the terminal oxyethylene group of POE, but the peptide side-chain and lowfield backbone NH resonances are well resolved. In trifluoroethanol the Boc-&Met),-NH-POE heptamer and octamer adopt the right-handed a-helical structure, and the present nmr studies provide evidence for two strong intramolecular hydrogen bonds to stabilize the helices. In water, the N-deblocked derivatives, (L-Met),-NH-POE oligomers adopt P-sheet structure and manifest well-resolved nonequivalent NH resonances with 6-7 Hz 3 J~~. c~ coupling constants.

Poly(ethylene oxide-co-β-benzyl l-aspartate) Block Copolymers: Influence of the Poly(ethylene oxide) Block on the Conformation of the Poly(β-benzyl l-aspartate) Segment in Organic Solvents

“…On the basis of this information, we studied our copolymers by 1 H NMR in deuterated chloroform and in DMSO- d 6 . Although Ribeiro et al reported that the NMR spctra of PEO-bound polypeptides in CDCl 3 are quantitatively similar to those of the corresponding low molecular weight peptides and that PEO segments have little effect on the peptides structure, , we found that the PEO segments induce changes in the structure of the PBLA blocks. Indeed, the comparison of the 1 H NMR spectrum in CDCl 3 of the PEO/PBLA block copolymer (Figure a) and of the mixture of the PEO and PBLA homopolymers (Figure b) gave evidence of these changes: the lateral methylene protons adjacent to the benzyl group of the PBLA segments appeared as a single peak at 5.05 ppm in the case of the mixture of homopolymers whereas it gave two doublets centered at 5.05 ppm and at 5.15 ppm for the PEO/PBLA block copolymer.…”