[NH:1]([C:15]([O:17][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:16])[C@H:2]([C:12](O)=[O:13])[CH2:3][CH2:4][C:5](=[O:11])[O:6][C:7]([CH3:10])([CH3:9])[CH3:8].CN1CCOCC1.ClC(OCC)=O.[BH4-].[Na+].OS([O-])(=O)=O.[K+]>C1COCC1.CO>[C:7]([O:6][C:5](=[O:11])[CH2:4][CH2:3][C@H:2]([NH:1][C:15]([O:17][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:16])[CH2:12][OH:13])([CH3:10])([CH3:8])[CH3:9]
In analogy to G. Kokotos (Synthesis 1990, 299), a solution of 5.00 g (14.8 mmol) of Z-Glu(OtBu)-OH in 74.0 ml of THF was treated at −10° C. with 1.63 ml (14.8 mmol) of 4-methylmorpholine, 1.41 ml (14.8 mmol) of ethyl chloroformate. After 10 min 1.682 g (44.5 mmol) of natriumborohydrid was added in one portion. Methanol (148 ml) was then added dropwise over a period of 25 min at 0° C. The solution was stirred 20 min, and then neutralized with a 10% KHSO4 solution. The organic solvents are evaporated under reduced pressure and the obtained residue is poured on a 10% KHSO4 extracted with EtOAc (3×). The organic phases were washed with aqueous 10% KHSO4, 10% NaCl, dried over Na2SO4 and evaporated to yield 5.16 g (quantitative) of the titled compound as yellow oil. MS: 324.18 (MH+).
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