1 hydroxybenzotriazole hydrate hobt

All reagents and solvents were purchased from commercial vendors and used without purification. 4-Amino-2-methoxybenzoic acid (97%), N,N-diisopropylethylamine (DIPEA, >98%), N,N-diethylethylenediamine (DEDA, >98%), ammonium hydroxide (NH₄OH), iodine monochloride, and trifluoroacetic acid (TFA, 99%) were purchased from ACROS Organics (Morris, NJ, USA). 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was obtained from Biosynth Carbosynth (Berkshire, UK). 1-Hydroxybenzotriazole hydrate (HOBt) and 5-fluoropyridine-2-carboxylic acid (98%) were purchased from AK Scientific, Inc. (Union City, CA, USA). 6-Fluoronicotinic acid (98%) was purchased from Accela ChemBio Co., Ltd. (Shanghai, China). Magnesium sulfate (MgSO₄), potassium carbonate (K₂CO₃), and thionyl chloride (SOCl₂) were obtained from Merck KGaA (Darmstadt, Germany). Thin-layer chromatography (TLC) was performed by silica gel F254-coated aluminum-backed plates (Merck KGaA, Darmstadt, Germany). Nuclear magnetic resonance (NMR) spectra were determined by the Bruker 400 UltraShield NMR spectrometer (Bruker, Billerica, MA, USA) at the Instrumentation Resource Center of National Yang-Ming University (Taipei, Taiwan). The radioactivity was measured by the γ-counter (PerkinElmer 1470 Automatic Gamma Scintillation, PerkinElmer Inc., Shelton, CT, USA).