Cl.[F:2][CH:3]([F:10])[CH:4]([NH2:9])[CH2:5][C:6]([OH:8])=[O:7].[C:11](OC([O-])=O)([O-])=O.[C:18](=[O:21])(O)[O-:19].[Na+].[Cl-].[Na+].O1[CH2:29][CH2:28][CH2:27]C1>O>[F:2][CH:3]([F:10])[CH:4]([NH:9][C:18]([O:19][C:28]([CH3:27])([CH3:29])[CH3:11])=[O:21])[CH2:5][C:6]([OH:8])=[O:7]A mixture of 4,4-difluoro-3-amino-butanoic acid, hydrochloride prepared as in Step C (0.702 g, 4 mM), ditertiobutyl dicarbonate (0.916 g, 4.2 mM), sodium bicarbonate (0.336 g, 4 mM) in tetrahydrofuran and water (6 ml of a 1:1 mixture) is heated at reflux for 48 hours. The resulting solution is saturated with sodium chloride and extracted three times with chloroform. The organic phase is dried over anhydrous magnesium sulfate, and the solvent evaporated in vacuo yielding a colorless oil.
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