1H and 13C n.m.r. studies of pseudo-peptide analogues of the C-terminal tetrapeptide of gastrin

1H and 13C n.m.r. study of pseudo-peptide analogues of the C-terminal tetrapeptide of gastrin, obtained by replacing each peptide bond by a "reduced peptide bond", one at a time, e.g. Boc-Trp psi (CH2NH)Leu-Asp-Phe-NH2 2, Boc-Trp-Leu psi (CH2NH) Asp-Phe-NH2 3, Boc-Trp-Leu-Asp psi (CH2NH)Phe-NH2 4, were reported. The CH2NH bond was completely characterized. 1H and 13C spectroscopic data were reported. It appeared from the present work that the modifications produced by the replacement of a peptide bond by a CH2NH bond were localized around the CH2NH.