2 hydroxyphenylacetic acid

All reagents were of analytical purity and were used without further purification. 2-hydroxyphenylacetic acid, LiOH, NaOH, KOH, RbOH, CsOH, potassium persulfate (K₂S₂O₈), copper(II) chloride (CuCl₂), iron(III) chloride hexahydrate (FeCl₃·6H₂O), (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), ammonium acetate (CH₃COONH₄), 2,9-dimethyl-1,10-phenanthroline (neocuproine), sodium acetate trihydrate (C₂H₃NaO₂∙3H₂O), 2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ), were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Methanol was purchased from Merck (Darmstadt, Germany).

Sodium hydroxide (NaOH), potassium hydroxide (KOH), aqueous ammonia (NH4OH), gentisic acid (2,5-dihydroxybenzoic acid), and ascorbic acid (AA) were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). HGA was obtained from MP Biomedicals, LLC (Illkirch, France) and 2-hydroxyphenylacetic acid from Sigma-Aldrich Co. (St. Louis, MO).

Quercetin, isorhamnetin, tamarixetin, and 3-coumaric acid were purchased from Extrasynthese. Quercetin-3′-sulfate, Quercetin-3-glucuronide, and isorhamnetin-3-glucuronide were synthetized as described [45 (link)]. xanthine oxidase (from bovine milk), allopurinol, 6-mercaptopurine, hypoxanthine, xanthine, uric acid, oxipurinol, 3-phenylpropionic acid, 3-(4-hydroxyphenyl)propionic acid, 3-(2,4-dihydroxyphenyl)propionic acid, 2-hydroxyphenylacetic acid, 4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, 3-hydroxy-4-methoxyphenylacetic acid, 4-(hydroxymethyl)phenylacetic acid, benzoic acid, 4-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, hippuric acid, 2,4-dihydroxyacetophenon, 4-methylcatechol, resorcinol, pyrogallol, phloroglucinol, 4-methoxysalicylic acid, and homovanillic acid were obtained from Sigma-Aldrich (St. Louis, MO, US). 3-(3-hydroxyphenyl)propionic acid and 3-(3,4-dihydroxyphenyl)propionic acid were purchased from Toronto Research Chemicals. 6-thiouric acid was obtained from Carbosynth, 6-thioxanthine was purchased from 5A Pharmatech. uric acid was dissolved in 0.01 M sodium hydroxide (2 mM), while Q and its metabolites, APU, 6-MP, 6-TX, 6-TU, and xanthine were dissolved in dimethyl sulfoxide (each 2 mM) and stored at –20 °C.