Isolation and detailed 1H and 13C NMR structural assignment for three trachylobanes from Psiadia punctulata (Asteraceae) grown in Africa

Abstract

The first isolation of a trachylobane from an African specimen of Psiadia punctulata (Asteraceae) is presented in this paper. A complete 1H and 13C NMR spectral analysis of this compound and two other trachylobane diterpenes, previously isolated from the same plant, are also provided. The use of NMR techniques such as gCOSY, gHSQC, gHMBC and 2D-J-resolved, in combination with a software-assisted methodology, led to a complete and unequivocal assignment of 1H and 13C signals. This was achieved together with the measurement of all homonuclear hydrogen coupling constants. The presented detail level of the assignment data has never been published before for trachylobanes. Furthermore, with all determined NMR experimental data from the spectra and to obtain a reliability assessment, signals were simulated in the FOMSC3 and NMR_MultSim software.