13C NMR sequence analysis, 10. Synthesis and spectroscopic characterization of sequence polypeptides containing taurine, γ‐aminopropanesulfonic acid, and sulfanilic acid

Starting with benzyloxycarbonyltauryl chloride (1) and benzyloxycarbonylsulfanilyl chloride as well as with glycine ethyl ester and β-alanine methyl ester several Z-tripeptides (3a–c, 7a–d) were synthesized. The sulfanilyl peptides 7a–d were converted to the 4-(isothiocyanato)benzenesulfonyl dipeptides 9a–d, which were condensed to the sequence polymers 10a–d at 140–170°C. From the Z-tauryl peptides 3a–c the free tripeptides 5a–c were prepared and condensed to the ternary sequence polypeptides 16a–c using the phosphorus triazolides 13 and 14 as condensing reagents. Starting with dipeptides 4a–d and 6a–d the binary sequence polymers 15a–d and 17a–d were obtained in like fashion. The 1H NMR spectra of these oligo- and poly-peptides were recorded in trifluoroacetic acid and 13C NMR spectra of the polypeptides in dimethyl sulfoxide and trifluoroacetic acid. Both 1H NMR and 13C NMR spectra allow characterization of and clear distinction between isomeric oligopeptides, i.e. Z-Sulf-Gly-β-Ala/Z-Sulf-β-Ala-Gly, and isomeric polypeptides, i.e. poly(Tau-γ-Abu)/poly(γ-Aps-β-Ala) or poly(Tau-Gly-β-Ala)/poly(Tau-β-Ala-Gly). A change of the solvent from dimethyl sulfoxide to trifluoroacetic acid results in a downfield shift of the 13C-carbonyl signals of the sequence polypeptides by about 10ppm, whereas the other C-signals show only small effects (<2ppm). The influence of monomer structure, sequence, and solvent on chemical shift is discussed.