N12CCCCC1C=NCCC2.Br[C@@H](CO)C(O)=[O:15].[CH:19]1([N:25]=[C:26]=[N:27][CH:28]2[CH2:33][CH2:32][CH2:31][CH2:30][CH2:29]2)[CH2:24][CH2:23][CH2:22][CH2:21][CH2:20]1.[Cl-].C([NH2+]CSC(C)(C)C)C1C=CC=CC=1>O1CCCC1>[C:26]([NH:25][CH:19]1[CH2:20][CH2:21][CH2:22][CH2:23][CH2:24]1)([NH:27][CH:28]1[CH2:33][CH2:32][CH2:31][CH2:30][CH2:29]1)=[O:15]
5 ml of a 2M solution of 1,5-diazabicyclo[5.4.0]-undec-5-ene (DBU) in tetrahydrofuran are added while stirring, at room temperature, to a solution of 845 mg (5 mmol) of 2-(S)-bromo-3-hydroxypropionic acid in 10 ml of absolute tetrahydrofuran and the resulting mixture is stirred for a further 2 hours at room temperature. The solvent is subsequently distilled off in vacuo and 25 ml of methylene chloride are added. To this solution containing the DBU salt of (R)-glycidic acid there are added 1.03 g (5 mmol) of dicyclohexyl carbodiimide and, after stirring for one hour, 1.3 g (5 mmol) of N-benzyl-N-tert.-butylthiomethylammonium chloride. After the addition of the last-mentioned reaction component, crystalline dicyclohexylurea is formed. After a reaction time of 3 hours at room temperature, the latter is filtered off with suction and the filtrate is diluted with methylene chloride and washed with phosphate buffer solution having a pH of 8. After concentration of the organic phase by evaporation, the residue is chromatographed over 50 g of silica gel. After a few first fractions have been removed with toluene, the title compound is eluted with a mixture of toluene/ethyl acetate (9:1) in the form of a colourless, viscous oil.
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