Cl.[CH2:2]([O:4][C:5](=[O:10])[C@H:6]([CH3:9])[NH:7][CH3:8])[CH3:3].[H-].[Na+].[C:13]([S:16][CH2:17][CH2:18][C:19](Cl)=[O:20])(=[O:15])[CH3:14].C(=O)(O)[O-].[Na+]>O1CCCC1>[CH2:2]([O:4][C:5](=[O:10])[C@@H:6]([N:7]([C:19](=[O:20])[CH2:18][CH2:17][S:16][C:13](=[O:15])[CH3:14])[CH3:8])[CH3:9])[CH3:3]The solution of 15 g (89.5 mmol) of N-methylalanine ethyl ester-hydrochloride in 850 ml of anhydrous tetrahydrofuran is mixed at 23° C. with 4.1 g of an approximately 60% sodium hydride dispersion and, after 3 hours, with 23.5 g of 3-acetylsulfanyl-propanoic acid chloride. It is allowed to react for two days, mixed with saturated sodium bicarbonate solution, and extracted several times with ethyl acetate. The combined organic extracts are washed with saturated sodium chloride solution, dried over sodium sulfate, and the residue that is obtained after filtration and removal of the solvent is purified by chromatography on fine silica gel. 17.6 g (67.3 mmol, 75%) of the title compound is isolated as a colorless oil.
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