Conformational studies on gastrin related peptides by high resolution 1H-n.m.r

The secondary structures of three gastrin analogs, HC1 X H-Trp-Nle-Asp(O-tBu)-Phe-NH2 (tetragastrin), pGlu-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH2 (octagastrin), and H-Leu-(Glu)5-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH2 (minigastrin) were studied by 1H-n.m.r. in dimethylsulfoxide and in trifluoroethanol. All three compounds were found to assume a random conformation in the former solvent, while some ordered secondary structure is present in trifluoroethanol even at the tetrapeptide level. This was shown by temperature studies and solvent titrations. At least four amide protons were found to be solvent shielded in the longer hormone.