Identification of Radical Scavenging Compounds in Rhaponticum carthamoides by Means of LC-DAD-SPE-NMR

A hyphenated LC-DAD-SPE-NMR setup in combination with on-line radical scavenging detection has been applied for the identification of radical scavenging compounds in extracts of Rhaponticum carthamoides. After NMR measurements, the pure compounds were infused into a mass spectrometer. The technique enabled selective detection and identification of individual radical scavenging compounds without any prior off-line chromatographic steps. Seven compounds, namely, quercetagetin-7--glucopyranoside (1), quercetagetin-7-(6' '-acetyl--glucopyranoside) (3), 6-hydroxykaempferol-7--glucopyranoside (2), 6-methoxykaempferol-3--glucopyranoside (4), 6-hydroxykaempferol-7-(6' '-acetyl--glucopyranoside) (5), chlorogenic acid (6), and -ecdysone (7), were identified in ethanol or aqueous extracts. Compound 5 is a new natural compound. Its radical scavenging activity was tested against DPPH radical and was found to be weaker than that of the reference antioxidants rosmarinic acid and Trolox