[OH:1][NH:2][C:3](=[NH:7])[CH:4]([CH3:6])[CH3:5].[H-].[Na+].[C:10]([O:14][C:15]([NH:17][CH2:18][CH2:19][C:20](OC)=O)=[O:16])([CH3:13])([CH3:12])[CH3:11].O>CN(C)C=O>[CH:4]([C:3]1[N:7]=[C:20]([CH2:19][CH2:18][NH:17][C:15](=[O:16])[O:14][C:10]([CH3:13])([CH3:12])[CH3:11])[O:1][N:2]=1)([CH3:6])[CH3:5]2.20 g (21.54 mmol) N-hydroxy-isobutyramidine are placed in 10 ml dimethylformamide and molecular sieve. 0.948 g (23.69 mmol) sodium hydride (60% in mineral oil) are added. The mixture is stirred for 0.1 hours at 50° C., then 6.20 g (30.51 mmol) methyl 3-tert-butoxycarbonylamino-propionate in 20 ml dimethylformamide are added. The reaction mixture is stirred for 3 hours at 50° C. After cooling 15 ml of water are added and the mixture is suction filtered through Celite. The 2 phases of the filtrate are separated, the aqueous phase is extracted with ethyl acetate, the combined organic phases are evaporated down. The residue is purified by chromatography.
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