Characterization of Deprotonated Constituents of Flavonoid-Rich Fraction from Cosmos caudatus Kunth. Leaves by UPLC-QToF-MS/MS

Abstract

The flavonoid-rich fraction from the ethanolic extract of the leaves of Cosmos caudatus Kunth. (Kenikir) was analyzed by ultra-performance liquid chromatography-mass spectrometry with a quadrupole and time-of-flight analyzer featuring an electrospray ionization source (QToF-ESI-MS/MS). The deprotonated molecules [M−H]⁻ were analyzed, and the flavonoids were tentatively annotated based on accurate mass and product-ion patterns. Chemical analysis of the fraction identified quercetin and three C-3 hydroxy group-substituted quercetin glycosides, namely quercetin 3-O-rutinoside (rutin), quercetin 3-O-β-D-glucopyranoside (isoquercitrin), and quercetin 3-O-arabinofuranoside. The results show that the fragmentation behavior of flavonol 3-O-glycosides can be analyzed based on the breakage of glycosidic link and interglycosidic linkages. Removal of the sugar moiety allows the distinctive product ions to be identified. Investigation of negative ion ESI-MS/MS spectra of flavonol O-glycosides allows their rapid characterization as flavonol 3-O-glycoside and enables their direct analysis in crude plant extracts. This study provides a detailed analysis of the MS/MS fragmentation pathways of 3-O-glycosylated flavonoids in a flavonoid-rich fraction of C. caudatus.