[NH2:1][CH2:2][C@H:3]([NH:7][C:8]([O:10][CH2:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1)=[O:9])[C:4]([OH:6])=[O:5].N#N.[CH3:20][C:21](=[CH2:23])[CH3:22].C([O-])(O)=O.[Na+]>O1CCOCC1.C(OCC)C>[NH2:1][CH2:2][C@H:3]([NH:7][C:8]([O:10][CH2:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1)=[O:9])[C:4]([O:6][C:21]([CH3:23])([CH3:22])[CH3:20])=[O:5]10 g (42 mmol) of (2S)-3-amino-2-benzyloxycarbonylaminopropionic acid were shaken in an autoclave at 20 atm. N2 pressure for 3 days in a mixture of 100 ml of dioxane, 100 ml of isobutylene and 8 ml of conc. H2SO4Excess isobutylene was blown out and 150 ml of diethyl ether and 150 ml of saturated NaHCO3 solution were added to the remaining solution. The phases were separated and the aqueous phase was extracted twice using 100 ml of diethyl ether each time. The combined organic phases were washed with 2×100 ml of H2O and dried over Na2SO4. After removing the solvent in vacuo, (1.1) were obtained as a pale yellow oil.
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