[NH2:1][C@H:2]([C:6]([OH:8])=[O:7])[CH:3]([CH3:5])[CH3:4].C(N([CH:15]([CH3:17])[CH3:16])CC)(C)C.[Br-:18].[OH-].[Na+]>CN(C=O)C.O.C1(C)C=CC=CC=1>[Br:18][C:16]1[CH:15]=[CH:17][C:3]([CH2:4][NH:1][C@H:2]([C:6]([OH:8])=[O:7])[CH:3]([CH3:5])[CH3:4])=[CH:2][CH:6]=152 mL (0.21 mol) of N,O-bistrimethylsilylacetamide is added under nitrogen atmosphere to a mixture made up of 23.5 g (0.20 mol) of L-valine and 38.5 mL (0.22 mol) of diisopropylethylamine in 12.5 mL of DMF. After 1 h at 80° C. the suspension changes to a clear solution. Then, in portions and controlling exothermy, 50 g (0.20 mol) of 4-bromobenzylo bromide is added and left to react at 80° C. for 2 h. The mixture is cooled to 20-25° C., 250 mL of toluene and a solution made up of 250 mL of water and 80 mL of NaOH 40% are added. The resulting aqueous phase is washed twice with 100 mL of AcOEt, the remains of solvent distilled and taken to pH 6-7 with HCl 3N. The solid obtained is filtered with 250 mL of IPA to give 43.9 g (76.5%) of N-(4-bromobenzyl)-L-valine.
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