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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 ϵ of the farthest accessible uv maximum as a function of the number of peptide bonds (nA). The peptide bond contribution proved to be independent of nA in the range nA = 1–5, thus ruling out the onset of helical conformations in the longer chain peptides.