Identification of Three Novel Polyphenolic Compounds, Origanine A-C, with Unique Skeleton from Origanum vulgare L. Using the Hyphenated LC-DAD-SPE-NMR/MS Methods

Identification of new compounds especially those with new skeletons from plant kingdom has long been a vital aspect for understanding phytochemistry, plant metabolisms and discovering new bioactive compounds. In this study, we identified and isolated three novel polyphenolic compounds, origanine A-C, from a well-researched plant Origanum vulgare L. using the hyphenated LC-DAD-SPE-NMR/MS methods. Based on the combined information from UV-visible, accurate mass and 2D NMR spectra together with computational calculations, we found that these compounds all had a novel skeleton of cyclohexenetetracarboxylic acids attached with some well-known bioactive moieties including 3,4-dihydroxyphenyl, 4-(beta-D-glucopyranosyloxy)benzyl alcohol (gastrodin), and 3-(3,4-dihydroxyphenyl)lactic acid (danshensu) residues. These findings provided crucial information to fill the gaps in our knowledge in terms of the plant secondary metabolism. This study also indicated the necessity for further research in plant secondary metabolism for even well-studied plants and demonstrated the powerfulness of the hyphenated LC-DAD-SPE-NMR/MS methods for comprehensive analysis of plant metabolites in particular for discovering new natural compounds.