[Cl:1][C:2]1[C:3]([CH3:18])=[C:4]([NH:10][C@H:11]([C@@H:15]([OH:17])[CH3:16])[C:12]([OH:14])=O)[CH:5]=[CH:6][C:7]=1[C:8]#[N:9].[C:19]([C:21]1[CH:30]=[CH:29][C:24]([C:25]([NH:27][NH2:28])=[O:26])=[CH:23][CH:22]=1)#[N:20]>>[Cl:1][C:2]1[C:3]([CH3:18])=[C:4]([NH:10][C@H:11]([C@@H:15]([OH:17])[CH3:16])[C:12]([NH:28][NH:27][C:25](=[O:26])[C:24]2[CH:23]=[CH:22][C:21]([C:19]#[N:20])=[CH:30][CH:29]=2)=[O:14])[CH:5]=[CH:6][C:7]=1[C:8]#[N:9](2R,3S)-2-(3-chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoic acid (intermediate 1a) (10.03 g, 37.3 mmol) and 4-cyano-benzohydrazide (6.02 g, 37.3 mmol) were coupled in an analogous procedure as described for the preparation of intermediate 3b. The crude product was purified by boiling in chloroform (100 mL) followed by cooling to 0° C. and filtration to yield product as a light yellow solid (12.05 g, 78%). 1H NMR (400 MHz, acetone-d6, δ in ppm) 9.81 (br s, 2H), 8.08 (AA′XX′, J=8.6 Hz, 2H), 7.91 (AA′XX′, J=8.7 Hz, 2H), 7.51 (d, J=8.7 Hz, 1H), 6.69 (d, J=8.8 Hz, 1H), 5.57 (d, J=7.0 Hz, 1H), 4.40 (m, 1H), 2.34 (dd, J=3.6, 6.9 Hz, 1H), 2.34 (s, 3H), 1.35 (d, J=6.4 Hz, 3H).
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