GENERAL METHODS: 1-chloro-4-hydroxyisoquinoline-3-carboxylic acid (300 mg, 1.35 mmol), methyl 2-aminoacetate (1.2 eq.), PyBOP (1.2 eq.), and triethylamine (Et3N, 1.5 mmol) were dissolved in anhydrous N,N-dimethylformamide (DMF, 5 mL) followed by stirring of the reaction for 24 h at room temperature. Upon completion of the reaction, DMF was removed by distillation under reduced pressure and the resulting residue was suspended in dichloromethane (CH2Cl2, 20 mL) and washed with deionized water (2 × 10 mL). The organic phase was dried over anhydrous magnesium sulfate (MgSO4), filtered and purified by column chromatography (using a Biotage SNAP KP-SIL TM 25g column with an elution system of cyclohexane/ethyl acetate, with the specific ratio adjusted according to the elution of each methyl ester). The purified product was dissolved in a solvent mixture of tetrahydrofuran (THF) and water (1:1, 10 mL), lithium hydroxide monohydrate (LiOH-H2O, 5 eq.) was added, and the reaction was stirred for 12 h at room temperature. Subsequently, THF was removed by distillation under reduced pressure and the remaining aqueous solution was neutralized with concentrated hydrochloric acid (HCl) to pH ≈ 7. If a precipitate was produced, the precipitate was collected by filtration and dried under vacuum to afford the target product 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido)acetic acid (20). If no precipitate was formed, the aqueous solution was extracted with ethyl acetate (EtOAc, 3 x 10 mL), the organic layers were combined, dried over anhydrous magnesium sulfate (MgSO4), filtered and concentrated under reduced pressure to give the target product.
Preparation of 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido)acetic acid (20): 1-chloro-4-hydroxyisoquinoline-3-carboxylic acid (300 mg, 1.35 mmol) was used as a starting material, and operated according to the above general method, the target compound (20) was finally obtained as a white solid (175 mg, 46% yield).
Characterization data:
1H NMR (400 MHz, DMSO-d6) δ = 9.16 (t, J = 6.0 Hz, 1H, NH), 8.30 (m, 1H, ArH), 8.24 (m, 1H, ArH), 7.84-8.09 (m, 2H, ArH), 4.02 (d, J = 6.0 Hz, 2H, CH2) ppm.
13C NMR (101 MHz, DMSO-d6) δ = 171.4, 169.6, 155.1, 139.4, 132.6, 132.5, 130.3, 129.3, 126.9, 123.8, 121.3, 41.7 ppm.
Melting Point (Mp): 212-214°C.
High Resolution Mass Spectrometry (HRMS, ESI-TOF) Calculated value C12H9ClN2NaO4 [M + Na+]: 303.0144, measured value: 303.0143.
Fourier transform infrared spectra (FT-IR, neat) νmax: 3402, 2915, 1712, 1641, 1354, 1255, 794 cm?1.
