[Cl:1][C:2]1[C:10]2[CH:9]([CH2:11][C:12]([O:14]CC)=[O:13])[O:8][B:7]([OH:17])[C:6]=2[CH:5]=[C:4]([O:18][C:19]2[CH:24]=[N:23][CH:22]=[CH:21][N:20]=2)[CH:3]=1.[OH-].[Li+].Cl>C1COCC1.O>[Cl:1][C:2]1[C:10]2[CH:9]([CH2:11][C:12]([OH:14])=[O:13])[O:8][B:7]([OH:17])[C:6]=2[CH:5]=[C:4]([O:18][C:19]2[CH:24]=[N:23][CH:22]=[CH:21][N:20]=2)[CH:3]=1To the solution of ethyl 2-(4-chloro-1-hydroxy-6-(pyrazin-2-yloxy)-1,3-dihydrobenzo[c][1,2]oxaborol-3-yl)acetate (110 mg, 0.316 mmol) in THF (2 mL) was added an aqueous solution of lithium hydroxide (66 mg, 1.58 mmol) in water (1 mL) at 0° C. The resulting mixture was stirred at 0° C. for 2 h, acidified with diluted hydrochloric acid at 0° C. to pH=1˜2 and extracted with EtOAc (2×20 mL). The combined organic layers were dried over anhydrous Na2SO4 and concentrated in vacuo. The residue was purified by prep HPLC to give the title compound as a white powder (66.9 mg, Yield: 83.5%). 1H NMR (400 MHz, DMSO-d6)δ 9.51 (s, 1H), 8.61 (s, 1H), 8.43 (s, 1H), 8.24 (s, 1H), 7.53 (s, 1H), 7.47 (s, 1H), 5.53-5.55 (d, J=8.4 Hz, 1H), 3.23-3.36 (d, J=15.6 Hz, 1H), 2.33-2.40 (m, 1H); MS (ESI) m/z=321 [M+H]+.
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