Reaction SMILES: [C:1]([O:5][C:6]([N:8]([CH2:13][C:14]([OH:16])=[O:15])[CH2:9][C:10]([OH:12])=O)=[O:7])([CH3:4])([CH3:3])[CH3:2].C1CCC(N=C=NC2CCCCC2)CC1>ClCCl>[C:1]([O:5][C:6]([N:8]1[CH2:9][C:10](=[O:12])[O:16][C:14](=[O:15])[CH2:13]1)=[O:7])([CH3:2])([CH3:3])[CH3:4]
Reactant: CC(C)(C)OC(=O)N(CC(=O)O)CC(=O)O
Agent: C(=NC1CCCCC1)=NC1CCCCC1
Solvent: ClCCl
Product: CC(C)(C)OC(=O)N1CC(=O)OC(=O)C1
Reaction time: 16 h
Yield: 98.1 %

Procedure:
A suspension of (tert-butoxycarbonyl-carboxymethyl-amino)-acetic acid (5 g, 21.4 mmol) and DCC (4.85 g, 23.6 mmol) in dichloromethane was stirred for 16 hours. The mixture was filtered and the solvent was removed from the filtrate to provide 2,6-dioxo-morpholine-4-carboxylic acid tert-butyl ester (4.86 g, 21.0 mmol, 99%). ({[2-(4-Bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetic acid: 2,6-Dioxo-morpholine-4-carboxylic acid tert-butyl ester (2.5 g, 11.6 mmol) was added to a solution of 2-amino-1-(4-bromo-phenyl)-ethanone hydrochloride (3.05 g, 12.2 mmol) and 4-methylmorpholine (1.92 mL, 17.4 mmol) in dimethylformamide (15 mL). After 30 min the solvent was removed under reduced pressure. The residue was taken up in ethyl acetate (100 mL) and washed with water (50 mL), aqueous hydrogen chloride (0.5 N, 2×50 mL), and saturated sodium bicarbonate (2×50 mL). The basic extracts were neutralized and extracted with ethyl acetate (2×75 mL). The combined organic phases from the second extraction were dried over sodium sulfate, and filtered. The solvent was removed under reduced pressure to provide ({[2-(4-bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetic acid (4 g, 9.3 mmol, 80%). C17H21BrN2O6 calculated 428.0 observed [M+1]+ 431.1; rt=2.36 min. 2-[2-({[2-(4-Bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetylamino]-3-methyl-butyric acid methyl ester: 4-Methylmorpholine (4.1 mL, 37.3 mmol) was added to a suspension of ({[2-(4-bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetic acid (4 g, 9.3 mmol), and HATU (4.61 g, 12.1 mmol) in dimethylformamide (25 mL). After 5 minutes d-valine methyl ester hydrochloride (1.56 g, 9.3 mmol), was added to the solution. After 1 hour the solvent was removed under reduced pressure. The residue was taken up in ethyl acetate (150 mL), and washed with water (100 mL), aqueous hydrogen chloride (0.5 N, 2×100 mL), saturated sodium bicarbonate (100 mL), and saturated sodium chloride (100 mL). The organic phase was dried over sodium sulfate, filtered and the solvent was removed under reduced pressure. The residue was subjected to flash chromatography with eluent of (10% methanol in ethyl acetate) and hexane. The product-containing fractions were combined and the solvent was removed under reduced pressure to yield 2-[2-({[2-(4-bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetylamino]-3-methyl-butyric acid methyl ester (4.37 g, 8.1 mmol, 87%). C23H32BrN3O7 calculated 541.1 observed [M+1]+ 431.1; rt=2.65 min. 2-[2-({[2-(4-Bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetylamino]-3-methyl-butyric acid: 2-[2-({[2-(4-Bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetylamino]-3-methyl-butyric acid was prepared using method 801 substituting 2-[2-({[2-(4-bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-ten-butoxycarbonyl-amino)-acetylamino]-3-methyl-butyric acid methyl ester for 4-oxo-hexahydro-PYrrolo[1,2-a]pyrazine-2,6-dicarboxylic acid 6-ethyl ester 2-methyl ester. C22H30BrN3O7 calculated 527.1 observed [M+1]+ 528.1; rt=2.39 min. 2-[2-({[2-(4-Bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-amino)-acetylamino]-3-methyl-butyric acid: 2-[2-({[2-(4-Bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-amino)-acetylamino]-3-methyl-butyric acid was prepared using method 804 substituting 242-({[2-(4-bromo-phenyl)-2-oxo-ethylcarbamoyl]-methyl}-tert-butoxycarbonyl-amino)-acetylamino]-3-methyl-butyric acid for 1-[5-(4′-{2-[1-(2-methoxycarbonylamino-3-methyl-butyryl)-pyrrolidin-2-yl]-3H-imidazol-4-yl}-biphenyl-4-yl)-1H-imidazol-2-ylmethyl]-2-oxo-piperidin-3-yl]-carbamic acid tert-butyl ester. C17H22BrN3O5 calculated 427.1 observed [M+1]+ 428.0; rt=2.39 min.