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0 °C

To a solution of [6-(5-aminomethyl-[1,3,4]thiadiazol-2-yloxy)-1-hydroxy-4-methyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl]-acetic acid ethyl ester (0.22 g, 0.6 mmol) in tetrahydrofuran (10 mL) at 0° C. was added lithium hydroxide (0.06 g, 2.42 mmol) in water (5 mL). The mixture was stirred at 0° C. for 1.5 hours then acidified to pH=2 with 2N HCl. The mixture was concentrated in vacuo and the residue purified by preparative HPLC to give [6-(5-aminomethyl-[1,3,4]thiadiazol-2-yloxy)-1-hydroxy-4-methyl-1,3-dihydro-benzo[c][1,2]oxaborol-3-yl]-acetic acid (0.015 g, 7%). 1H NMR (400 MHz, DMSO-d6) δ ppm 9.37 (s, 1H), 8.58 (br. s., 3H), 7.48 (s, 1H), 7.33 (d, J=1.62 Hz, 1H), 5.56 (dd, J=9.23, 2.52 Hz, 1H), 4.43 (s, 2H), 3.10 (dd, J=15.63, 2.71 Hz, 1H), 2.34 (s, 3H), 2.18 (dd, J=15.44, 9.21 Hz, 1H); MS (ESI) m/z: 336 [M+1]+; HPLC purity: 94.12% (MaxPlot), 96.99% (220 nm).

1. concentrationThe mixture was concentrated in vacuo
2. customthe residue purified by preparative HPLC