Assignment of All Proton, Carbon, and Nitrogen NMR Signals of Antamanide in Chloroform Solution

Homo‐ and heteronuclear one‐ and two‐dimensional techniques have been used to assign the ¹H, ¹³C, and ¹⁵N NMR spectra of the cyclic decapeptide antamanide (1) in CDCl₃. The assignment includes the aromatic resonances of phenylalanine and the non‐protonated nitrogen atoms of proline by means of heteronuclear two‐dimensional NMR spectroscopy. Sequence analysis of the four phenylalanine and four proline amino acid residues was performed by heteronuclear proton – carbon long‐range couplings using the COLOC sequence. Three new thiazolidine analogues of antamanide confirm the sequence analysis of prolines and open the possibility for the extraction of extended spectral parameters. The interpretation of NOE data, obtained from one‐ and two‐dimensional spectra at high field and low temperatures, demonstrate possible misinterpretations of this effect respecting sequence assignment, if only NOEs between NH protons and α‐protons are considered.