To a 100 mL, round-bottomed flask equipped with a magnetic stir bar and septum was added (2R,3R)-2-(3-chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoic acid (2.02 g, 7.5 mmol) followed by a addition of anhydrous THF (60 mL) under an atmosphere of nitrogen. Benzhydrazide (1.02 g, 7.5 mmol) was subsequently added and the mixture was cooled to −15° C. To this mixture was added HOBt (1.02 g, 7.5 mmol) followed by addition of EDC (2.88 g, 15.0 mmol) and lastly, TEA (3.2 mL, 23 mmol) was slowly added. The temperature of this reaction was maintained between −25° C. and −15° C. for a period of 1 h then allowed to warm to room temperature overnight. The solids were filtered off and washed with additional THF (20 mL) and EtOAc (20 mL). The mother liquor was then diluted with EtOAc (200 mL) and washed with 5% citric acid/water (2×50 mL), saturated sodium bicarbonate (1×25 mL), and brine (1×50 mL) then dried over sodium sulfate. The solution was then filtered and concentrated under reduced pressure using rotary evaporation to reveal a white solid. This was purified via silica gel chromatography eluted with 85% EtOAc/hexane to provide title compound as a white solid (1.49 g, 51%). 1H NMR (400 MHz, acetone-d6, δ in ppm) 9.64 (br s, 2H), 7.94 (m, 2H), 7.60 (m, 1H), 7.51 (m, 3H), 6.73 (d, J=8.7 Hz, 1H), 5.59 (d, J=7.2 Hz, 1H), 4.71 (br s, 1H), 4.24 (m, 1H), 4.12 (dd, J=5.1, 7.3 Hz, 1H), 2.35 (s, 3H), 1.39 (d, J=6.3 Hz, 3H).
