[Cl:1][C:2]1[CH:3]=[C:4]([NH:10][C@H:11]([CH2:20][NH:21][CH2:22][CH3:23])[CH2:12][C:13](OC(C)(C)C)=[O:14])[CH:5]=[CH:6][C:7]=1[C:8]#[N:9].Cl.C([O-])([O-])=O.[K+].[K+]>CO>[Cl:1][C:2]1[CH:3]=[C:4]([NH:10][C@H:11]2[CH2:12][C:13](=[O:14])[N:21]([CH2:22][CH3:23])[CH2:20]2)[CH:5]=[CH:6][C:7]=1[C:8]#[N:9]A solution of 1,1-dimethylethyl (3S)-3-[(3-chloro-4-cyanophenyl)amino]-4-(ethylamino)butanoate (5.66 g, 16.8 mmol), HCl (4M in dioxane, 40 mL) and MeOH (100 mL) was stirred at 65° C. for 2 h. After cooling, the reaction was concentrated. To the residue, K2CO3 (325 mesh, 6.6 g, 47.5 mmol) and MeOH (150 mL) were added and the reaction was stirred at 65° C. for 1 h. Solvent was removed and the residue was partitioned between EtOAc and H2O. The organic layer was dried over MgSO4 and concentrated to give the product as a white solid (2.4 g, 54%). LC-MS (ES) m/e 264.4 (M+H)+.
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