Cl.[CH3:2][O:3][C:4](=[O:9])[C@H:5]([CH2:7][OH:8])[NH2:6].C(N(CC)CC)C.[CH3:17][Si:18]([CH3:33])([CH3:32])[CH2:19][CH2:20][O:21][C:22](=O)[O:23]N1C(=O)CCC1=O>ClCCl>[CH3:2][O:3][C:4](=[O:9])[CH:5]([NH:6][C:22]([O:21][CH2:20][CH2:19][Si:18]([CH3:33])([CH3:32])[CH3:17])=[O:23])[CH2:7][OH:8]To a mixture of 1.25 g serine methyl ester hydrochloride, 2.25 ml triethylamine and 10 ml dichloromethane was added at 0° C. a solution of 2.22 g carbonic acid 2,5-dioxo-pyrrolidin-1-yl ester 2-trimethylsilanyl-ethyl ester [R. E. Shute, D. H. Rich, Synthesis, 1987, 346]. After stirring for 24 h at rt the reaction mixture was washed two times with 1N potassium hydrogen sulfate, once with saturated sodium bicarbonate solution and once with brine. The organic phase was dried over magnesium sulfate, filtered and evaporated to give 2.29 g of a colorless liquid.
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