(2R)-2-acetamido-3-sulfanylpropanamide

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a stirring suspension at room temperature under N2 of (S)-3-(1-(tert-butoxycarbonyl)-1H-imidazol-5-yl)-2-(3-(tert-butoxycarbonylamino)propanamido)propanoic acid (45c, 35.74 g, 83.80 mmol) and (R)-2-acetamido-3-mercaptopropanamide (45b, 13.59 g, 83.78 mmol) in 500 mL of THF:EtOAc (1:1) was added dropwise triethylamine (26 mL, 186 mmol). After addition, the suspension was stirred for 15 minutes then propylphosphonic anhydride, 50 wt. % solution in EtOAc (55 mL, 92 mmol) was added dropwise. The resultant cloudy solution was stirred at room temperature for 2 h then saturated NaHCO3 solution (˜500 mL) was added. The layers were separated and the organic extract was washed with saturated KH2PO4 and then saturated NaCl solution. The aqueous phases were back extracted (in the same order) with fresh EtOAc (2×500 mL). The combined organic extracts were dried using MgSO4, filtered, concentrated and chromatographed twice (silica gel, 50% THF in EtOAc) to give 35.53 g (74%) of tert-butyl 5-((S)-3-((R)-2-acetamido-3-amino-3-oxopropylthio)-2-(3-(tert-butoxycarbonylamino)propanamido)-3-oxopropyl)-1H-imidazole-1-carboxylate (45d) as white foamy solid. MS (APCI) m/z 571 [M+H]+. After addition The resultant cloudy solution was stirred at room temperature for 2 h The layers were separated the organic extract was washed with saturated KH2PO4 The aqueous phases were back extracted (in the same order) with fresh EtOAc (2×500 mL) The combined organic extracts were dried filtered concentrated chromatographed twice (silica gel, 50% THF in EtOAc)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 45a (53.4 g, 0.30 mol) was diluted with 250 mL of toluene and 200 mL of ammonium hydroxide. The mixture was stirred at room temperature overnight then concentrated. The resulting residue was suspended in 250 mL of acetonitrile/H2O (9.3:1) and stirred at room temperature until the insoluble material formed a viscous paste. The solvent was decanted then concentrated to give a viscous liquid. The crude product was taken up in dichloromethane/methanol (8.5:1) and passed through a silica gel column eluting with dichloromethane/methanol (8.5:1). Fractions containing the least polar UV-active component were combined and concentrated to give 25 g (52%) of (R)-2-acetamido-3-mercaptopropanamide as white solid. 1HNMR (DMSO-d6) δ 8.0 (d, 1H), 7.41 (s, 1H), 7.13 (s, 1H), 4.33 (m, 1H), 2.76 (m, 1H), 2.65 (m, 1H), 2.22 (m, 1H), 1.88 (s, 3H). then concentrated stirred at room temperature until the insoluble material formed a viscous paste The solvent was decanted then concentrated to give a viscous liquid eluting with dichloromethane/methanol (8.5:1) Fractions containing the least polar UV-active component concentrated

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 45a (53.4 g, 0.30 mol) was diluted with 250 mL of toluene and 200 mL of ammonium hydroxide. The mixture was stirred at room temperature overnight then concentrated. The resulting residue was suspended in 250 mL of acetonitrile/H2O (9.3:1) and stirred at room temperature until the insoluble material formed a viscous paste. The solvent was decanted then concentrated to give a viscous liquid. The crude product was taken up in dichloromethane/methanol (8.5:1) and passed through a silica gel column eluting with dichloromethane/methanol (8.5:1). Fractions containing the least polar UV-active component were combined and concentrated to give 25 g (52%) of (R)-2-acetamido-3-mercaptopropanamide as white solid. 1HNMR (DMSO-d6) δ 8.0 (d, 1H), 7.41 (s, 1H), 7.13 (s, 1H), 4.33 (m, 1H), 2.76 (m, 1H), 2.65 (m, 1H), 2.22 (m, 1H), 1.88 (s, 3H). then concentrated stirred at room temperature until the insoluble material formed a viscous paste The solvent was decanted then concentrated to give a viscous liquid eluting with dichloromethane/methanol (8.5:1) Fractions containing the least polar UV-active component concentrated

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a stirring suspension at room temperature under N2 of (S)-3-(1-(tert-butoxycarbonyl)-1H-imidazol-5-yl)-2-(3-(tert-butoxycarbonylamino)propanamido)propanoic acid (45c, 35.74 g, 83.80 mmol) and (R)-2-acetamido-3-mercaptopropanamide (45b, 13.59 g, 83.78 mmol) in 500 mL of THF:EtOAc (1:1) was added dropwise triethylamine (26 mL, 186 mmol). After addition, the suspension was stirred for 15 minutes then propylphosphonic anhydride, 50 wt. % solution in EtOAc (55 mL, 92 mmol) was added dropwise. The resultant cloudy solution was stirred at room temperature for 2 h then saturated NaHCO3 solution (˜500 mL) was added. The layers were separated and the organic extract was washed with saturated KH2PO4 and then saturated NaCl solution. The aqueous phases were back extracted (in the same order) with fresh EtOAc (2×500 mL). The combined organic extracts were dried using MgSO4, filtered, concentrated and chromatographed twice (silica gel, 50% THF in EtOAc) to give 35.53 g (74%) of tert-butyl 5-((S)-3-((R)-2-acetamido-3-amino-3-oxopropylthio)-2-(3-(tert-butoxycarbonylamino)propanamido)-3-oxopropyl)-1H-imidazole-1-carboxylate (45d) as white foamy solid. MS (APCI) m/z 571 [M+H]+. After addition The resultant cloudy solution was stirred at room temperature for 2 h The layers were separated the organic extract was washed with saturated KH2PO4 The aqueous phases were back extracted (in the same order) with fresh EtOAc (2×500 mL) The combined organic extracts were dried filtered concentrated chromatographed twice (silica gel, 50% THF in EtOAc)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 45a (53.4 g, 0.30 mol) was diluted with 250 mL of toluene and 200 mL of ammonium hydroxide. The mixture was stirred at room temperature overnight then concentrated. The resulting residue was suspended in 250 mL of acetonitrile/H2O (9.3:1) and stirred at room temperature until the insoluble material formed a viscous paste. The solvent was decanted then concentrated to give a viscous liquid. The crude product was taken up in dichloromethane/methanol (8.5:1) and passed through a silica gel column eluting with dichloromethane/methanol (8.5:1). Fractions containing the least polar UV-active component were combined and concentrated to give 25 g (52%) of (R)-2-acetamido-3-mercaptopropanamide as white solid. 1HNMR (DMSO-d6) δ 8.0 (d, 1H), 7.41 (s, 1H), 7.13 (s, 1H), 4.33 (m, 1H), 2.76 (m, 1H), 2.65 (m, 1H), 2.22 (m, 1H), 1.88 (s, 3H). then concentrated stirred at room temperature until the insoluble material formed a viscous paste The solvent was decanted then concentrated to give a viscous liquid eluting with dichloromethane/methanol (8.5:1) Fractions containing the least polar UV-active component concentrated