Hydrochloric Acid → 4-[5-(5-Diethylaminomethyl-4-methyl-thiophen-2-yl)-[1,2,4]oxadiazol-3-yl]-benzoic acid

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Reaction Steps

4-[5-(5-Diethylaminomethyl-4-methyl-thiophen-2-yl)-[1,2,4]oxadiazol-3-yl]-benzoic acid ethyl ester (1.42 g) is prepared starting from 4-(N-hydroxycarbamimidoyl)-benzoic acid ethyl ester (1.01 g, 4.84 mmol) and 5-diethylaminomethyl-4-methyl-thiophene-2-carboxylic acid (1.00 g, 4.40 mmol) according to Method A; LC-MS: tR=0.63 min; [M+1]+=400.12; 1H NMR (CDCl3): δ 1.11 (t, J=7.0 Hz, 6H), 1.45 (t, J=7.0 Hz, 3H), 2.26 (s, 3H), 2.64 (q, J=7.0 Hz, 4H), 3.73 (s, 2H), 4.44 (q, J=7.3 Hz, 2H), 7.69 (s, 1H), 8.16-8.20 (m, 2H), 8.22-8.25 (m, 2H). This material (1.42 g, 3.58 mmol) is dissolved in 2 M LiOH in methanol (50 mL) and the mixture is stirred at rt for 20 h before it is acidified by adding aq. HCl. The mixture is extracted twice with EA. The combined organic extracts are dried over MgSO4, filtered and concentrated. The crude product is purified by prep. HPLC to give 4-[5-(5-diethylaminomethyl-4-methyl-thiophen-2-yl)-[1,2,4]oxadiazol-3-yl]-benzoic acid (710 mg) as a white solid; LC-MS: tR=0.52 min; [M+1]+=372.14. b) To a solution of 4-[5-(5-diethylaminomethyl-4-methyl-thiophen-2-yl)-[1,2,4]oxadiazol-3-yl]-benzoic acid (400 mg, 1.08 mmol) in DMF (5 mL), HOBt (160 mg, 1.19 mmol) followed by EDC HCl (227 mg, 1.19 mmol) is added. The mixture is stirred at rt for 5 min before ethanolamine (72 mg, 1.19 mmol) is added. The reaction mixture is stirred at rt for 1 h. The mixture is diluted with EA and washed with sat. aq. NaHCO3. The washing is extracted back twice with EA. The combined organic extracts are dried over MgSO4, filtered and concentrated. The crude product is purified by CC on silica gel eluting with DCM containing 4% of methanol to give the title compound (290 mg) as a white solid; LC-MS: tR=0.47 min; [M+1]+=415.14; 1H NMR (CDCl3): δ1.11 (t, J=7.0 Hz, 6H), 2.26 (s, 3H), 2.64 (q, J=7.0 Hz, 4H), 3.67-3.72 (m, 2H), 3.73 (s, 2H), 3.90 (t, J=4.8 Hz, 2H), 6.69 (t br, J=5.3 Hz, 1H), 7.68 (s, 1H), 7.91-7.95 (m, 2H), 8.22-8.26 (m, 2H).

Provenance & Evidence