Cl.[CH2:2]([O:4][P:5]([CH2:10][CH2:11][NH2:12])(=[O:9])[O:6][CH2:7][CH3:8])[CH3:3].[C:13](Cl)([O:15][CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:14].CCN(C(C)C)C(C)C>C(Cl)Cl.CCOC(C)=O>[CH2:7]([O:6][P:5]([CH2:10][CH2:11][NH:12][C:13]([O:15][CH2:16][C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)=[O:14])(=[O:9])[O:4][CH2:2][CH3:3])[CH3:8]The HCl salt of (2-amino-ethyl)-phosphonic acid diethyl ester (4.5 g, 20.7 mmol) was dissolved in CH2Cl2 (100 mL). To this solution was added CBzCl (3.2 mL, 22.7 mmol), followed by iPr2NEt (14.4 mL, 82.8 mmol). The reaction was stirred at room temperature until complete, as determined by TLC (eluent: 100% EtOAc). The reaction was quenched by the addition of saturated NaHCO3. The mixture was then partitioned between CH2Cl2 and H2O. The layers were separated and the organic layer was washed with brine and then dried over Na2SO4. The drying agent was removed by vacuum filtration and (2-benzyloxycarbonylamino-ethyl)-phosphonic acid diethyl ester was isolated from the concentrated filtrate by silica gel column chromatography (EtOAc/hexanes) (5.98 g, 92%).
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