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 C₁₈ 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 C₁₈ column. This setup allowed the HPLC-PDA-HRMS-SPE-NMR analysis of 23 coumarins, including six new compounds, 8-O-β-d-glucopyranosyloxy-6-(2,3-dihydroxy-3-methylbut-1-yl)-7-methoxycoumarin (4), (Z)-6-(4-β-d-glucopyranosyloxy-3-methylbut-2-en-1-yl)-7-hydroxycoumarin (6), 6-(4-β-d-glucopyranosyloxy-3-methylbut-1-yl)-7-hydroxycoumarin (8), (Z)-7-(4-β-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 C₁₈ 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.

Synthetic Studies on Aromatic Heterocyclic Compounds

This review covers the concise synthesis of simple coumarin with salicyl aldehydes and Wittig reagent, and a convenient synthesis of polycyclic aromatic heterocyclic compounds using the aryl-aryl coupling reaction of aryl benzamides and aryl benzoates with a Pd reagent is presented. In the first section, the reactions of salicyl aldehydes with OMe, OH, Br, CO(2)Me, and NO(2) groups with carbethoxymethylenetriphenylphophorane are described. Specifically, the reaction of 3-nitrosalicylaldehyde with amines gave benzoxazoles in moderate yield. In the second section, the syntheses of benzo[c]phenanthridine alkaloids, quinazoline alkaloids, and graphislactones in the Pd-mediated biaryl coupling reaction are described. Moreover, the synthesis of benzonaphthazepine and pyrrolophenanthridine alkaloids utilizing regioselective C-H activation with intramolecular coordination of a benzylamine to Pd is described, and the effects of oxygen substituents in the benzoyl part of benzanilides on the coupling position in its biaryl coupling reaction are presented. An effective Pd reagent for the coupling reaction of aryl tolyflate and arene was developed.