Six methyl-substituted phloroglucinol glycosides (1-6) were isolated from Agrimonia pilosa, including four new compounds (1-3, 6). The aglycones (1a-4a) of 1-4 and their corresponding oxidized products (1c-4c) were also obtained from A. pilosa. The structures were determined by a series of spectroscopic analyses and chiral separation. Notably, the structures of aglycones 1a-4a were unstable and prone to oxidation spontaneously, to yield the dearomatized structures 1c-4c. The mechanism of oxidative dearomatization was disclosed as a free-radical chain reaction with 3O2 by the techniques of HPLC-HR-MS2, EPR spectra and DFT-calculation, and hydroperoxide was defined as the intermediate.
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