15N NMR spectroscopy. 23—Shift effects of protecting groups in oligopeptides of glycine and alanine

The natural abundance 15N NMR spectra of glycylglycine and alanylalanine derivatives with various N- or O-protecting groups were measured in dimethyl sulphoxide, pyridine and fornic acid. The nitrogens directly attached to the protecting group have chemical shifts relative to NO3− in the range −220 to −358 ppm. The influence of the amino end group on the next peptide nitrogen (Gly-Gly bond) amounts to, at most, 1.7 ppm. The influence of the O-protecting group is also weak (Δ δ⩽2 ppm), but strongly dependent on the solvent.

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