Reaction solvents

DpS, salicylic acid (SA), sodium nitrite (NaNO₂), sulfamic acid, and 2,4-dinitrobenzene sulfonic acid (DNBS) were purchased from the Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Sulfasalazine (SSZ) was purchased from Sigma-Aldrich Chemical Co. Inc. (St. Louis, MO, USA). Reaction solvents and high-performance liquid chromatography (HPLC) grade solvents were obtained from Junsei Chemical Co. (Tokyo, Japan) and Daejung Chemicals & Metals Co. Ltd. (Gyeonggi-do, Siheung, Korea), respectively. Cytokine-induced neutrophil chemoattractant-3 (CINC-3) enzyme-linked immunosorbent assay (ELISA) kit was purchased from R&D Systems Inc. (Minneapolis, MN, USA). Phosphate buffer saline (pH 7.4) was purchased from Thermo Fisher Scientific (Waltham, MA, USA). All other chemicals used were commercially available reagent-grade reagents. Spots on thin-layer chromatography (TLC) plates (silica gel F₂₅₄s, Merck Millipore, Burlington, MA, USA) were detected using an ultraviolet lamp (254 nm). Infrared (IR) and ¹H-NMR spectra were taken by a Varian FT-IR spectrophotometer (Varian Medical Systems, Palo Alto, CA, USA) and a Varian AS 500 NMR spectrophotometer (Varian Medical Systems, Palo Alto, CA, USA), respectively. The chemical shift in the NMR spectra is presented in ppm, downfield from that of tetramethylsilane.

ASP hydrochloride (HCl), salicylic acid, sodium nitrite (NaNO₂), sulfamic acid, and 5-ASA were purchased from Tokyo Kasei Kogyo Co. (Tokyo, Japan). SSZ and 2, 4-dinitrobenzenesulfonic acid hydrate (DNBS) were purchased from Sigma Chemical Co. Inc. (St. Louis, MO, USA). Phosphate-buffered saline (pH 7.4, PBS) was purchased from Thermo Fisher Scientific (Waltham, MA, USA). Reaction solvents were obtained from Junsei Chemical Co. (Tokyo, Japan). All other chemicals were reagent grade, commercially available products. Spots on thin-layer chromatography (TLC) plates (silica gel F₂₅₄s, Merck Millipore, Burlington, MA, USA) were detected using a UV lamp (at 254 nm). IR spectra were recorded using a Varian FT-IR spectrophotometer (Varian, Palo Alto, CA, USA). ¹H-NMR spectra were recorded using a Varian AS 500 spectrometer (Varian). The chemical shifts in NMR spectra were reported in ppm downfield from tetramethylsilane.