Reaction Steps
Step A. 2(S)-tert-Butoxycarbonylamino-3-(2-nitrophenyl-amino)-propionic acid. 2-tert-Butoxycarbonylamino-3-aminopropionic acid (10 g, 49 mmol), 2-fluoronitrobenzene (5.7 ml, 54 mmol), and sodium bicarbonate (8.25 g, 98 mmol) was taken into 130 ml of dimethylformamide and heated at 80° C. for 18 hours. The reaction was evaporated in vacuo to give a viscous orange residue that was dissolved in 300 ml of water and extracted with diethyl ether (3×150 ml). The aqueous solution was acidified to pH 5 with 10% sodium hydrogen sulfate and extracted with ethyl acetate (3×250 ml). The combined extracts were dried over anhydrous sodium sulfate, filtered, and evaporated to give 12.64 g (83%) of the title compound as an orange amorphous solid. 1H NMR (CD3OD) δ 8.15-8.10 (1H, d), 7.54-7.48 (1H, t), 7.13-7.08 (1H, d), 6.73-6.65 (1H, t), 4.45-4.35 (1H, m), 3.9-3.8 (1H, dd), 3.65-3.55 (1H, dd), 1.45 (9H, s). Step B. 2(S)-tert-Butoxycarbonylamino-3-(2-aminophenyl-amino)-propionic acid. A mixture of 2-tert-Butoxycarbonylamino-3-(2-nitrophenylamino)propionic acid (12.65 g, 40.5 mmol) and 0.5 g of 10% Pd/C in 100 ml of methanol under hydrogen at 1 atmosphere was stirred for 4 hrs. The solution was filtered through Celite 545 and the filtrate evaporated in vacuo to afford 11.95 g of the title compound in quantitative yield as a dark brown solid that was used without purification. 1H NMR (CD3OD) δ 6.75-6.70 (3H, m), 6.65-6.58 (1H, m), 4.35-4.3 (1H, m), 3.6-3.38 (2H, m), 1.45 (9H, s). Step C. 3(S)-tert-Butoxycarbonylamino-1,3,4,5-tetrahydro-benzo[b][1,4]diazepin-2-one. 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (8.54 g, 44.5 mmol) was added to a cooled (0° C.) solution of 2-tert-butoxycarbonylamino-3-(2-aminophenylamino)propionic acid (11.95 g, 40.5 mmol) in 100 ml of dimethylformamide and stirred for 18 hours. The reaction was poured into 700 ml of ethyl acetate and washed four times with 100 ml of water. The organic layer was dried over anhydrous sodium sulfate, filtered, and evaporated to give a brown solid that was purified by flash chromatography eluting with 3:7 ethyl acetate/hexane to give 8 g (71%) of the title compound: 1H NMR (CDCl3) 67.78 (1H, s), 7.02-6.95 (1H, m), 6.88-6.82 (1H, m), 6.82-6.78 (1H, m), 6.75-6.70 (1H, m), 5.8-5.7 (1H, d), 4.55-4.45 (1H, m), 3.95 (1H, s), 3.9-3.82 (1H, m), 3.48-3.40 (1H, m), 1.45 (9H, s). Step D. (3(S)-tert-Butoxycarbonylamino-2-oxo-2,3,4,5-tetrahydrobenzo[b][1,4]diazepin-1-yl)acetic acid methyl ester (103). A 1.0 M solution of lithium bis(trimethylsilyl)amide (3.4 ml, 3.4 mmol) in THF was added dropwise to a −78° C. solution of 3-tert-butoxycarbonylamino-1,3,4,5-tetrahydrobenzo[b][1,4]diazepin-2-one (0.94 g, 3.38 mmol) in 20 ml of anhydrous tetrahydrofuran and stirred for 30 minutes. Methyl bromoacetate (0.44 ml, 4 mmol) was added dropwise to the reaction mixture then warmed to room temperature. The reaction was diluted with 100 ml of ethyl acetate and washed with 0.3N potassium hydrogen sulfate (50 ml), water (2×50 ml), and brine. The combined organics were dried over anhydrous sodium sulfate, filtered, and evaporated to afford a gum that was purified by flash chromatography eluting with 3:7 EtOAc/Hex. to give 0.98 g (83%) of the title compound as a white solid. 1H NMR (CDCl3) δ 7.15-7.07 (2H, m), 6.98-6.94 (1H, m), 6.88-6.84 (1H, d), 5.62-5.55 (1H, d), 4.71-4.65 (1H, d), 4.65-4.6 (1H, m), 4.33-4.27 (1H, d), 3.96-3.90 (1H, m), 3.78 (3H, s), 3.44-3.37 (1H, m), 1.4 (9H, s).
