Structure of the adduct of alantolactone with (Z)-L-Cys-Ala-OMe; H-1 and C-13 assignment of the alantolactone moiety by NMR at 14 T

Analysis of the H-1-H-1 NOE effects observed for S(11,13-dihydroalantolacton-13-yl)-L-cysteinyl-L-alanine methyl ester in (CD3)(2)SO 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 H-1 spectrum of the alantolactone moiety is in excellent agreement with the experimental data, The complete assignments of the C-13 signals of alantolactone, its peptide adduct and four dipeptide precursors are based on one- and two-dimensional H-1-C-13 NMR techniques.