Triethylamine → N'-((2R,3R)-2-(3-Chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoyl)-4-nitrobenzohydrazide

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(2R,3R)-2-(3-chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoic acid (intermediate 1a) (8.3 g, 30.9 mmol), 4-nitrobenzohydrazide (6.16 g, 34.0 mmol) and anhydrous THF (200 mL) were placed in a 500 mL round bottomed flask and the mixture was cooled to −50° C. 1-Hydroxybenzotriazole hydrate (4.2 g, 30.9 mmol) was added to the mixture together with N-(3-Dimethylaminopropyl)-N′-ethylcarbodimide HCl (7.34 g, 38.3 mmol) at −50° C. followed by triethylamine (5.3 mL, 38.3 mmol). The reaction mixture was maintained at −15° C. and stirred for 1 h after which stirring continued overnight while the mixture slowly warmed to room temperature. After 18 h the mixture was filtered under vacuum and the residue washed with THF (50 mL). The THF solution was concentrated to ca. 20 mL, whereupon ethyl acetate (200 mL) was added followed by water (100 mL). The phases were partitioned and the organic phase washed with water (150 mL), brine (150 mL), dried (Na2SO4) and concentrated to furnish a light yellow solid as the title compound (15.9 g, 80%) that was used without further purification. 1H NMR (400 MHz, d6-acetone, δ in ppm) 9.88 (br s, 2H), 8.35 (d, 6.7 Hz, 2H), 8.16 (d, J=6.7 Hz, 2H), 7.53 (d, J=7.5 Hz, 1H), 6.69 (d, J=7.5 Hz, 1H), 5.56 (d, J=6.6 Hz, 1H), 4.46-4.36 (m, 4.18-4.10 (m, 1H), 3.26 (s, 3H), 1.37 (d, J=7.4 Hz, 3H).

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