C([O:3][C:4](=[O:21])[CH2:5][CH:6]1[O:10][B:9]([OH:11])[C:8]2[CH:12]=[C:13]([O:19][CH3:20])[CH:14]=[C:15]([CH2:16][O:17][CH3:18])[C:7]1=2)C.[Li+].[OH-].Cl>C1COCC1.O>[OH:11][B:9]1[C:8]2[CH:12]=[C:13]([O:19][CH3:20])[CH:14]=[C:15]([CH2:16][O:17][CH3:18])[C:7]=2[CH:6]([CH2:5][C:4]([OH:21])=[O:3])[O:10]1
To a solution of (1-hydroxy-6-methoxy-4-methoxymethyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl)-acetic acid ethyl ester (60 g, 0.20 mmol) in THF (3 mL) and H2O (2 mL) was added LiOH (0.048 g) at 0° C. The resulting mixture was stirred at room temperature for 2 hours then cooled to 0° C. and acidified to pH 3 with 6N HCl. The mixture was concentrated in vacuo and the residue purified by silica gel flash column chromatography to give (1-hydroxy-6-methoxy-4-methoxymethyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl)-acetic acid (0.050 g, 90%). 1H NMR (400 MHz, DMSO-d6) δ 7.12 (s, 1H), 6.94 (s, 1H), 5.56 (m, 1H), 4.40 (m, 2H), 3.75 (s, 3H), 3.26 (s, 3H), 3.00 (m, 1H), 2.02 (m, 1H). MS (ESI) m/z: 235 [M−1]−. HPLC purity: 86% (220 nm), 96% (Maxplot).
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