Influence of D and L amino-acid residues on the conformation of peptides in solution: A carbon-13 nuclear magnetic resonance study of cyclo(prolyl-leucyl)

✍ Scribed by Roxanne Deslauriers; Z. Grzonka; Roderich Walter

• Publisher: Wiley (John Wiley & Sons)
• Year: 1976
• Tongue: English
• Weight: 375 KB
• Volume: 15
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1976.360150905

✦ Synopsis

Abstract

The ^13^C chemical shifts and spin‐lattice relaxation times are reported for cyclo(L‐Pro‐L‐Leu) and cyclo(L‐Pro‐D‐Leu). The chemical shifts of the D and L leucyl residues in the cyclic peptides differ from each other by 1.8 and 3.6 parts per million for the α and β carbons, respectively. The α‐carbons of the prolyl residues differ by 1.0 ppm as a consequence of proximity to a D or an L leucyl residue. The ^13^C spin‐lattic relaxation time(T~1~) of the prolyl residues, but not the leucyl residues, in both compounds are indicative of difference in conformational equilibria within the pyrrolidine ring in the L‐L isomer as compared to the L‐D isomer. Anisotropic overall molecular reorientation is not responsible for the differences observed in the T~1~ values. The differences in T~1~ values and chemical shifts between cyclo(L‐Pro‐L‐Leu) and cyclo(L‐Pro‐D‐Leu) appear to result from a difference in conformations of the two diketopiperazine rings.