Citric Acid → (2R,3S)-2-(3-chloro-4-cyanophenylamino)-3-hydroxybutanoic acid

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2-chloro-4-fluorobenzonitrile (60702-69-4) (2.0 g, 12.86 mmol) was mixed together with H-D-Thr-OH (1.84 g, 15.43 mmol) in DMSO (30 mL). K2CO3 (3.73 g, 27.0 mmol) was added to the reaction mixture and stirred at 75° C. for 24 h. The reaction mixture was cooled down to room temperature and poured slowly into a 10% citric acid solution and stirred for 10 min at room temperature. The solution was extracted with EtOAc several times to get the crude product. The crude product was chromatographed with a gradient of hexane EtOAc and then with EtOAc, 100% to get the pure final product 1.8 g): 1H NMR (500 MHz, acetone-d6, δ in ppm) 7.51 (d, J=9 Hz, 1H), 6.95 (s, 1H), 6.82 (d, J=9 Hz, 1H), 5.17 (d, J=9 Hz, 1H), 4.42 (m, 1H), 4.22 (d, J=6 Hz, 1H), 2.34 (s, 3H), 1.28 (d, J=6 Hz, 3H).

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