Structure of the Adduct of Alantolactone with (Z)-L-Cys-Ala-OMe; 1H and 13C Assignment of the Alantolactone Moiety by NMR at 14 T

Analysis of the 1H–1H NOE effects observed for S-(11,13-dihydroalantolacton-13-yl)-L-cysteinyl-L-alanine methyl ester in (CD3)2SO at 14 T showed that the 7- and 11-protons are in cis positions. The distances between 7-, 8- and 11-protons of the adduct were derived by a semi-quantitative approach based on analysis of NOESY cross peaks and a computed molecular model. The simulated 1H spectrum of the alantolactone moiety is in excellent agreement with the experimental data. The complete assignments of the 13C signals of alantolactone, its peptide adduct and four dipeptide precursors are based on one- and two-dimensional 1H–13C NMR techniques.