Co-oligopeptides of aromatic amino acids and glycine with a variable distance between the aromatic residues. III. Co-oligopeptides of L-phenylalanine, L-tryptophan, and Glycine: synthesis and ultraviolet absorption properties.

The preparation of the co-oligopeptides of the series H-Gly-Phe-(Gly)_n-Trp-Gly-OH (n = 0, 1, 2) and of other free peptides of glycine, L -tryptophan, and L -phenylalanine is reported. The syntheses have been carried out by conventional methods, using N-hydroxysuccinimide esters for the coupling steps. The ultraviolet absorption properties of the free peptides have been investigated in water. No hypo- or hyperchromicity was found for the aromatic chromophores, with the exception of H-Gly-Phe-Trp-OH, which shows a small but significant hypochromicity. The contribution of the peptide bond to the molar absorptivity in the far ultraviolet has been separated from that of the side chain plus the ? COO^? group by plotting the measured molar absorptivity ? of the farthest accessible uv maximum as a function of the number of peptide bonds (n_A). The peptide bond contribution proved to be independent of n_A in the range n_A = 1–5, thus ruling out the onset of helical conformations in the longer chain peptides.