Acetic Acid Mixture with Hydrobromic Acid → {5-Aminomethyl-2-[4-(6-chloro-benzo[b]thiophene-2-sulfonyl)-2-oxo-piperazin-1-ylmethyl]-thiazol-4-yl}-acetic acid ethyl ester

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{5-(Benzyloxycarbonylamino-methyl)-2-[4-(6-chloro-benzo[b]thiophene-2-sulfonyl)-2-oxo-piperazin-1-ylmethyl]-thiazol-4-yl}-acetic acid ethyl ester (40 mg, 0.06 mmol) is treated with 30% HBr/HOAc (1 mL) for 7 h. Ether (10 mL) is added and the resulting precipitate is washed twice with ether. The resulting salt is partitioned between EtOAc (15 mL) and NaHCO3 solution (10 mL). The organic phase is washed with NaHCO3 and brine (2×10 mL), dried (MgSO4) and concentrated to provide {5-aminomethyl-2-[4-(6-chloro-benzo[b]thiophene-2-sulfonyl)-2-oxo-piperazin-1-ylmethyl]-thiazol-4-yl}-acetic acid ethyl ester. 1H NMR (300 MHz, DMSO) δ 8.32 (d, 1H), 8.17 (s, 1H), 8.08-8.02 (m, 2H), 7.57 (dd, 1H), 4.62 (s, 2H), 4.02 (q, 2H), 3.81 (s, 2H), 3.74 (s, 2H), 3.64 (s, 2H), 3.48-3.35 (m, 4H), 2.48 (t, 3H); MS (ion spray) 543 (M+H)+.

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