[C:1]([O:5][C:6](=[O:10])[C@@H:7]([CH3:9])[NH2:8])([CH3:4])([CH3:3])[CH3:2].C(N(CC)C(C)C)(C)C.[N:20]([CH:23]([CH2:29][CH2:30]Br)[C:24](OCC)=[O:25])=[N+:21]=[N-:22].[I-].[Na+]>C(#N)C>[N:20]([CH:23]1[CH2:29][CH2:30][N:8]([C@H:7]([CH3:9])[C:6]([O:5][C:1]([CH3:4])([CH3:3])[CH3:2])=[O:10])[C:24]1=[O:25])=[N+:21]=[N-:22]To a solution of D-alanine tert-butylester (1.28 g) and N,N-diisopropylethylamine (1.22 ml) in acetonitrile (15 ml), was added a solution of ethyl 2-azido-4-bromobutanoate (1 g) and sodium iodide (0.02 g) in acetonitrile (5 ml). The mixture was heated at 60° C. for 60 h and then concentrated under pressure to give a brown oil. This oil was partitioned between DCM and water. The separated organic layer was washed further with water and dried (over magnesium sulphate), and concentrated under reduced pressure. The residual brown oil was purified using Biotage™ chromatography (silica, eluting with cyclohexane;ethyl acetate 3:1) to give the title compound (0.204 g) as a mixture of two diastereoisomers.
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