Detailed 1H and 13C NMR structural assignment and relative stereochemistry determination for three closely related sesquiterpene lactones.

ABSTRACT

A complete analysis of (1)H and (13)C NMR spectra of the trypanocidal sesquiterpene lactone eremantholide C and two of its analogues is described. These structurally similar sesquiterpene lactones were submitted to (1)H NMR, (13)C {(1)H} NMR, gCOSY, gHSQC, gHMBC, J-resolved and DPFGSE-NOE NMR techniques. The detailed analysis of those results, correlated to some computational calculations (molecular mechanics), led to the total and unequivocal assignment of all (1)H and (13)C NMR data. The determination of all (1)H/(1)H coupling constants and all signal multiplicities, together with the elimination of previous ambiguities were also achieved.