COC(=O)[CH2:4][NH:5][CH2:6][C@H:7]1[CH2:11][CH2:10][CH2:9][N:8]1[C:12]([O:14]C(C)(C)C)=O.FC(F)(F)C(O)=O>C(Cl)Cl>[CH2:6]1[NH:5][CH2:4][C:12](=[O:14])[N:8]2[CH2:9][CH2:10][CH2:11][C@H:7]121,1-Dimethylethyl (2R)-2-({[2-(methyloxy)-2-oxoethyl]amino}methyl)-1-pyrrolidinecarboxylate (D3; 800 mg, 2.94 mmol) was dissolved in methylene chloride (10 ml) and treated with trifluoroacetic acid (2.5 ml) for 2 h. The reaction mixture was loaded as such on a SCX column and the non-basic compounds were washed away with methanol. The ninhydrine-positive fractions eluted with 1M methanolic ammonia were concentrated under vacuum at 40° C. for 30 min, isolating the title compound as a pale yellow oil: 410 mg, 2.92 mmol, 99% yield.
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