A structural and spectroscopic study on carquejol, a relevant constituent of the medicinal plant Baccharis trimera (Less.) DC. (Asteraceae)

摘要

AbstractCarquejol and its acetate are monoterpenoids based on the rareo-menthane skeleton and distinctive components of the essential oil fromBaccharis trimera. Carquejol was characterized by using Fourier Transform infrared (FT-IR) and Raman (FT-Raman), Ultraviolet–Visible (UV–Visible), Electronic Circular Dichroism (ECD), Mass, Hydrogen and Carbon Nuclear Magnetic Resonance (1H and13C NMR) and 2D1H1H gCOSY,1H13CgHSQC,1H13CgHMBC spectroscopies. Due to the chirality of this monoterpenoid, six different structures were analysed, of which only four showed higher populations and minimal energies. The natural bond orbital (NBO), atoms in molecules (AIM), Merz-Kollman (MK) charges, molecular electrostatic potentials (MEP) and frontier orbitals studies were performed in order to evaluate their structural, electronic, topological and vibrational properties. All calculations were performed by using the hybrid B3LYP method and the 6-31G* and 6-311++G** basis sets. The comparison of the experimental ECD spectra with the corresponding theoretical ones confirm the (4S,5R) configuration assigned to carquejol. The force fields for the most stable configurations were computed by using those two levels of theory and the complete vibrational assignments for the two conformations of carquejol are reported. The different orientations and directions of the dipole moments of the two structures and the proximity in the nucleophilic indexes with those reported for other terpenes could justify in part the potential biological properties reported for carquejol. The MEP surfaces for both structures reveal that the nucleophilic and electrophilic sites of higher reactivity are principally centred on the OH groups.Graphical abstractDisplay OmittedHighlights?Carquejol was characterized by FT-IR, FT-Raman, UV–Vis, ECD and NMR spectroscopies.?Due to the chirality of this monoterpenoid, six different structures were analysed.?The ECD spectrum confirm the (4S,5R) configuration of carquejol.?The nucleophilic and electrophilic sites are centred on the OH groups.?The vibrational assignments of the 69 normal vibration modes was reported.]]>