Advancing HPLC-PDA-HRMS-SPE-NMR Analysis of Coumarins in Coleonema album by Use of Orthogonal Reversed -Phase C18 and Pentafluorophenyl Separations

A hyphenated procedure involving high-performance liquid chromatography, photodiode array detection, high-resolution mass spectrometry, solid-phase extraction, and nuclear magnetic resonance spectroscopy, i.e., HPLC-PDA-HRMS-SPE-NMR, has proven an effective technique for the identification of compounds in complex matrices. Most HPLC-PDA-HRMS-SPE-NMR investigations reported so far have relied on analytical-scale reversed-phase C-18 columns for separation. Herein is reported the use of an analytical-scale pentafluorophenyl column as an orthogonal separation method following fractionation of a crude ethyl acetate extract of leaves of Coleonema album on a preparative-scale C-18 column. This setup allowed the HPLC-PDA-HRMS-SPE-NMR analysis of 23 coumarins, including six new compounds, 8-O-beta-D-glucopyranosyloxy-6-(2,3-dihydroxy-3-methylbut-1-yl)-7-methoxycoumarin (4), (Z)-6-(4-beta-D-glucopytanosyloxy-3-methylbut-2-en-1-yl)-7-hydroxycoumarin (6), 6-(4-beta-D-glucopyranosyloxy-3-methylbut-1-yl)-7-hydroxycoumarin (8), (Z)-7-(4-beta-D-glucopyranosyloxy-3-methylbut-2-en-1-yloxy)coumarin (13), (S)-8-(3-chloro-2-hydroxy-3-methylbut-1-yloxy)-7-methoxycoumarin (19), and 7-(3-chloro-2-hydroxy-3-methylbut-1-yloxy)coumarin (20). The use of the pentafluorophenyl column even allowed separation of several regioisomers that are usually difficult to separate using reversed-phase C-18 columns. The phytochemical investigation described for C. album in this report demonstrates the potential and wide applicability of HPLC-PDA-HRMS-SPE-NMR for accelerated structural identification of natural products in complex mixtures.