3 3 4 dihydroxyphenyl propanoic acid

Theaflavins (TF), theaflavin-3-gallate (TF2A), theaflavin-3′-gallate (TF2B), and theaflavin-3,3′-digitate (TF3), all with purities of 98%, were purchased from Chengdu Munster Biotechnology Co., Ltd. (Chengdu, China). Gallic acid, pyrogallol, 4-hydroxybenzoic acid, 3-hydroxyphenylacetic acid, phenylacetic acid, and 3-(3′,4′-dihydroxyphenyl) propanoic acid, all with purities of at least 98%, were purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China).
2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ) were purchased from Sinopharm Chemical (Shanghai, China). Acetonitrile (LC/MS grade) was obtained from Merck (Darmstadt, Germany). Formic acid (LC/MS grade) was purchased from Fisher Scientific (Loughborough, UK). Deionized water (18.2 MΩ/cm) was prepared by distilling water through a Milli-Q water purification system (Millipore, Billerica, MA, USA). Other reagents were all of analytical grade.

The standard substances EGCG, EGC, ECG, and EC, all with a purity of 98%, were purchased from Chengdu Munster Biotechnology Co., Ltd. (Chengdu, China). Gallic acid, Pyrogallol, 4-phenylbutyric acid, 3-phenylpropionic acid, phenylacetic acid, 3-(3′,4′-dihydroxyphenyl)propanoic acid, 2-(4′-hydroxyphenyl)acetic acid, 2-(3′,4′-dihydroxyphenyl)acetic acid, and 4-hydroxybenzoic acid, all with purities of at least 98%, were obtained from Yuanye Bio-Technology Co., Ltd. (Shanghai, China). 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), α-glucosidase, α-amylase, 3,5-dinitrosalicylic acid (DNS), and P-nitrophenyl-α-D-glucopyranoside (pNPG) were also purchased from Yuanye Bio-Technology Co., Ltd. (Shanghai, China).
The mass spectrometer (MS)-grade methanol, acetonitrile, and formic acid of the guaranteed reagent were purchased from Thermo Fisher Scientific Co. (Waltham, MA, USA). Deionized water (>18.2 MΩ/cm) was prepared using distilled water processed via a Milli-Q water purification system (Millipore, Billerica, MA, USA). Other reagents were of analytical grade.