C([O-])(O)=O.[Na+].[NH2:6][C@@H:7]([C:11]([OH:13])=[O:12])[C@H:8]([CH3:10])[OH:9].[C:14](Cl)(=[O:25])[O:15][CH2:16][CH2:17][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1>C1COCC1.O.[Br-].C([N+](CCCC)(CCCC)CCCC)CCC>[OH:9][C@@H:8]([CH3:10])[C@@H:7]([NH:6][C:14]([O:15][CH2:16][CH2:17][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:25])[C:11]([OH:13])=[O:12]In a round bottom flask, NaHCO3 (5.94 g, 70.7 mmol) was suspended in THF (15 mL) and water (30 mL), then D-threonine (3.34 g, 28.0 mmol) was added. 3-phenylpropyl chlorocarbonate (6.2 g, 31.2 mmol) was slowly added, followed by a catalytic amount (0.3 g) of tetrabutylamonium bromide. After stirring 18 h at rt., the mixture was diluted with water (100 mL), washed twice with Et2O (2×100 mL) and pH adjusted to 2 with 2M HCl solution. The aqueous phase was extracted with AcOEt (3×150 mL), the collected organic phases were dried over Na2SO4, filtered and the solvent removed under vacuum to give the title compound (1.43 g, 18%), as colorless oil, which was used in the next step without further purification. Rf=0.38 (Cy/AcOEt 2:8+1% CH3COOH). FTIR (cm−1): 3340 (br), 3064, 3030, 2982, 2939, 1730 (br), 1528, 1374, 1241, 1094, 1072, 1048, 781, 749, 703.
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