Isolation and structure elucidation of caryophyllane sesquiterpenoids from leaves of Eremophila spathulata

Crude extract of Eremophila spathulata leaves was investigated by semi-preparative scale high-performance liquid chromatography (HPLC), analytical scale HPLC, and hyphenated high-performance liquid chromatography-photodiode array-high-resolution mass spectrometry-nuclear magnetic resonance (HPLC-PDA-HRMS-SPE-NMR), which afforded seven previously unreported caryophyllane sesquiterpenoids. Semi-preparative scale separation of the crude extract afforded (1R*,4R*,9S*,E)-8-formyl-11,11-dimethylbicyclo7.2.0]undec-7-ene-4-carboxylic acid (5) and analytical-scale HPLC separation afforded (1R*,4S*,7S*,9S*)-7-hydroxy-11,11-dimethyl-8-methylenebicyclo7.2.0]undecane-4-carboxylic acid (1), (1S*,6R*,9R*,E)-10,10-dimethylbicyclo7.2.0]undec-2-ene-2,6-dicarboxylic acid (2), (1R*,4S*,9S*)-11,11-dimethyl-8-oxobicyclo7.2.0]undecane-4-carboxylic acid (3), and (1R*,4R*,9S*)-11,11-dimethyl-8-oxobicyclo7.2.0]undecane-4-carboxylic acid (4). HPLC-PDA-HRMS-SPE-NMR afforded (1R*,4R*,9S*)-11,11-dimethyl-8-methylenebicyclo7.2.0]undecane-4-carboxylic acid (6) and (1R*,4S*,9S*)-11,11-dimethyl-8-methylenebicyclo7.2.0]undecane-4-carboxylic acid (7). The structures of all isolated compounds were established based on HRMS as well as extensive 1D and 2D NMR analysis. Relative configurations were determined by correlations in spectra from rotational Overhauser effect spectroscopy.