CO-OLIGOPEPTIDES CONTAINING 2 AROMATIC RESIDUES SPACED BY GLYCYL RESIDUES .10. PROTON MAGNETIC-RESONANCE STUDY OF CO-OLIGOPEPTIDES OF TRYPTOPHAN AND GLYCINE

The 1H‐nmr spectra of co‐oligopeptides of tryptophan and glycine with structure H‐Gly‐Trp‐(Gly)n‐Trp‐Gly‐OH (n = 0–2) and those of several di‐ and tripeptides have been recorded at 360 MHz with CD3OD solutions containing 0.1N NaOD. The assignment of resonance signals was generally possible by comparing the spectra of structurally related peptides with each other. In order to solve the remaining ambiguities in the assignment, H‐(αL,βS)(α,β‐d2)Trp‐OH, H‐Trp‐(αL,βS)(α,β‐d2)Trp‐OH, and H‐Trp‐(δ1,ε2,ζ2,ζ3,η2‐d5)Trp‐OH have been prepared and their spectra compared with those of the undeuterated compounds. The distribution of rotamers around the χ1 and (in two cases) χ2 torsion angles of the side chains has been obtained from the vicinal coupling constants 3J H αH β and from the long‐range coupling constants 4J H βH δ1. These data and an analysis of the chemical shifts of the Gly‐Cα protons suggest that the orientation of the aromatic side chain is influenced by the following order of decreasing interaction with the functional groups at N‐ and C‐side: ‐NH2 > –NHCO– > –CONH–> –COO−. This rule does not hold for the second Trp residue of di‐ and tripeptides containing the ‐Trp‐Trp‐ sequence, which has tentatively been attributed to steric effects. Copyright © 1979 John Wiley & Sons, Inc.