LC-ESI-MS Study of the Flavonoid Glycoside Malonates of Red Clover (Trifolium pratense)

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Abstract
High-performance liquid chromatography−electrospray ionization−mass spectrometry (LC-ESI-MS) was applied to the analysis of the flavonoids and their glycoside malonates of the flowers and leaves of red clover (Trifolium pratense). Through LC-MS comparative studies on the plant extracts and their malonate-free extracts, ∼20 flavonoid glycoside malonates were detected in the flower extract. Eight were identified as genistin 6‘ ‘-O-malonate (39), formononetin 7-O-β-d-glucoside 6‘ ‘-O-malonate (40), biochanin A 7-O-β-d-glucoside 6‘ ‘-O-malonate (41), trifoside 6‘ ‘-O-malonate (42), irilone 4‘-O-β-d-glucoside 6‘ ‘-O-malonate (43), pratensein 7-O-β-d-glucoside 6‘ ‘-O-malonate (44), isoquercitrin 6‘ ‘-O-malonate (45), and 3-methylquercetin 7-O-β-d-glucoside 6‘ ‘-O-malonate (46). About 15 other flavonoids and clovamides were proved to be present in this extract. The study also found that the flowers contained flavones as the major flavonoids, whereas the leaves had isoflavones as the major flavonoids. This is the first detection of the six malonates (39 and 42−46) in the extracts of red clover, and among them, 42, 43, and 46 are new compounds. Keywords: Trifolium pratense; red clover; Leguminosae; flavonoids; flavonoid glycoside malonates; clovamides; LC-ESI-MS analysis