Reaction Steps
To a solution of (2S,3S,4S)-4-fluoro-3-methoxy-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester and (2R,3R,4R)-3-fluoro-4-methoxy-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester (300 mg, 1.14 mmol), 3,3-dimethylbutylamine (115 mg, 1.14 mmol) and HBTU (648 mg, 1.71 mmol) in CH2Cl2 (7 mL) was added DIPEA (0.60 mL, 3.42 mmol). The reaction mixture was stirred at RT under nitrogen atmosphere overnight and concentrated. The crude residue was taken-up in EtOAc, washed with 0.1 N HCl (×2), dried (Na2SO4), filtered and concentrated. The crude residue was purified by flash column chromatography on silica gel (c-hexane to c-hexane/EtOAc 6:4 in 40 min) to give (2S,3S,4S)-2-(3,3-dimethyl-butylcarbamoyl)-4-fluoro-3-methoxy-pyrrolidine-1-carboxylic acid tert-butyl ester: Rf, TLC (EtOAc)=0.5; 1H NMR (400 MHz, DMSO-d6) δ (ppm): 7.92 (m, 1H), 5.16 (dq, 1H), 4.29-4.37 (m, 1H), 4.15 (m, 1H), 3.72 (m, 1H), 3.39 (m, 1H), 3.35 (s, 3H), 3.08 (m, 2H), 1.32-1.40 (m, 11H), 0.90 (s, 9H) and (2R,3R,4R)-2-(3,3-dimethyl-butylcarbamoyl)-3-fluoro-4-methoxy-pyrrolidine-1-carboxylic acid tert-butyl ester: Rf, TLC (EtOAc)=0.6; 1H NMR (400 MHz, DMSO-d6) δ (ppm): 7.90 (m, 1H), 5.05 (m, 1H), 4.20 (t, 1H), 4.02 (m, 1H), 3.70 (m, 1H), 3.39 (m, 1H), 3.33 (overlap with DMSO, m, 1H); 3.27 (s, 3H), 3.06 (m, 2H), 1.36-1.43 (m, 11H), 0.89 (s, 9H)
