Metabolite Extraction and Derivatization Protocol

The metabolite standards were purchased from Sigma Aldrich (MO, USA), Tokyo Chemical Industry (Tokyo, Japan), Aladdin (Shanghai, China), J&K Chemicals (Beijing, China), and Toronto Research Chemicals (Toronto, Canada). The extraction solvents methanol and chloroform were obtained from Sinopharm Chemical Reagent (Beijing, China). Methoxyamine hydrochloride (MEOX, ≥98%), N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA, ≥98%), and anhydrous pyridine (≥99.5%) were used as derivatization reagents and were obtained from Sigma. Internal standards (ISs) of phenyl beta-D-glucopyranoside (TCI, ≥99%), hexanedioic acid (Aladdin, ≥99%), and L-norvaline (Aladdin, ≥99%) were used.