Conformations of cyclic peptides. V. A proton magnetic resonance study of evolidine, cyclo-ser-phe-leu-pro-val-asn-leu

The 220 MHz proton magnetic resonance spectrum of the cyclic heptapeptide evoli-dine, cyclo-Ser-Phe-Leu-Pro-Val-Asn-Leu, has been analyzed. From the temperature dependence of chemical shift of the peptide protons in dimethyl sulfoxide, it is concluded that the peptide protons of the Asn and Phe residues are shielded from the solvent. This observation and H-C_α-N-H dihedral angles, estimated from the corresponding coupling constants, are combined in a proposed conformation of the peptide backbone. The consistency of this conformation with other proton magnetic resonance observations is discussed.