Into a 50-mL round-bottom flask was placed a solution of ethyl 2-(6-(5-amino-1,3,4-thiadiazol-2-yloxy)-1-hydroxy-4-methyl-1,3-dihydrobenzo[c][1,2]oxaborol-3-yl)propanoate (500 mg, 1.32 mmol, 1.00 equiv, 96%) in H2O/THF (10/10 mL), then added lithium hydroxide hydrate (230 mg, 5.48 mmol, 4.00 equiv). The resulting solution was stirred for 2 h at room temperature. The resulting mixture was concentrated under vacuum. The residual solution was adjusted to pH 3 with HCl (1 mol/L) and stirred for 30 min at room temperature. The resulting mixture was concentrated under vacuum. The crude product (200 mg) was purified by Prep-HPLC with the following conditions: Column, Xbridge Prep Phenyl, 5 μm, 19×150 mm; Mobile phase, water (with 0.05% TFA) and CH3CN; Gradient, 17% CH3CN up to 30% in 8 min, up to 100% in 1.5 min; Detector, UV 220 & 254 nm. This resulted in 30.2 mg (6%) of 2-(6-(5-amino-1,3,4-thiadiazol-2-yloxy)-1-hydroxy-4-methyl-1,3-dihydrobenzo[c][1,2]oxaborol-3-yl)propanoic acid as a white solid. H-NMR (300 MHz, DMSO-d6, ppm): δ1.284 (3H, d, J=7.2 Hz), 2.332 (3H, s), 3.120 (2H, m), 5.301 (1H, d, J=2.7 Hz), 7.082-7.141 (3H, m), 7.295 (1H, d, J=2.1 Hz), 9.180 (1H, s). MS (ESI) m/z: 336 [M+H]+.
