3-Fluorobenzohydrazide → N'-((2R,3S)-2-(3-chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoyl)-3-fluorobenzohydrazide

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(2R,3S)-2-(3-chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoic acid (intermediate 1a) (2 g, 7.44 mmol) and 3-Fluorobenzohydrazide (1.26 g, 8.19 mmol) were mixed together in THF (100 ml) and cooled to −15° C. under N2 atmosphere. To the pre-cooled reaction mixture were added hydroxybenzotriazole (HOST) (1.0 g, 7.44 mmol), TEA (1.56 mL, 11.16 mmol) followed by N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDCl) (2.14 g, 11.16 mmol). The reaction mixture was allowed to stir at −20° C. for 20 min and then at room temperature overnight. After the reaction was complete based on TLC, the urea was filtered off and the solution was washed with 5% citric acid (2×80 mL), 5% NaHCO3 (2×80 mL) followed by water (80 mL) and then dried (Na2SO4) to provide the crude product as a yellow solid (2.75 g, 91%); 1H NMR (400 MHz, d6-acetone, δ in ppm) 9.84 (br s, 2H), 7.79-7.76 (m, 1H), 7.67-7.63 (m, 1H), 7.58-7.51 (m, 2H), 7.41-7.35 (m, 1H), 6.68 (d, J=9 Hz, 1H), 5.55 (d, J=9 Hz, 1H), 4.79 (br s, 1H), 4.42-4.36 (1H), 4.14-4.10 (m, 1H), 2.36 (s, 3H) and 1.36 (d, J=6.5 Hz).

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