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

Abstract

• New NMR data for three trachylobanes, are presented for the first time in Literature. • The presented data completely clarified the 1H and 13C NMR data assignments for these trachylobanes. • A new methodology, recently published, was applied to clarify all multiplicities, measuring all J values for all substances. • A stereochemistry clarification including W-coupling measuring is provided for each studied compound. The first isolation of a trachylobane from an African specimen of Psiadia punctulata (Asteraceae) is presented in this paper. A complete 1 H and 13 C 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 g COSY, g HSQC, g HMBC and 2D- J -resolved, in combination with a software-assisted methodology, led to a complete and unequivocal assignment of 1 H and 13 C 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.