Potassium Carbonate → Methyl 4-((tert-butoxycarbonyl)amino)-2-(2-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)-2-oxoethyl)-3-oxopentanoate

Participants

Reaction Steps

At RT, a solution of (R)-methyl 4-((tert-butoxycarbonyl)amino)-3-oxopentanoate (603) (5.38 g, 21.95 mmol) in 20 mL of THF and 20 mL of DMF was treated with 2-bromo-1-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)ethanone (606) (5.44 g, 16.18 mmol) and K2CO3 (5.59 g, 40.4 mmol) and stirred at RT for 6 h. It was diluted with 250 mL of EtOAc, filtered through a flitted funnel, rinsed with 2×15 mL of EtOAc. The filtrate was washed with sat NH4Cl (2×25 mL) followed by brine (15 mL). The organic solution was dried over Na2SO4 and concentrated. The residue was passed through a short column (35-75% EtOAc in hexanes) to get rid of the solvent front peaks and the base line peaks. Fractions with m/z (ESI, +ve) 501.2 (M+H)1 were collected and concentrated to give methyl 4-((tert-butoxycarbonyl)amino)-2-(2-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)-2-oxoethyl)-3-oxopentanoate (326a) as a brown residue. To the brown residue in a glass tube in 25 mL of EtOH and 10 mL of HOAc was added NH4OAc (8.46 g, 110 mmol). The tube was sealed and heated in an oil bath at 50° C. for 8 h. The mixture was concentrated to half of its volume, diluted with 250 mL of EtOAc, washed sequentially with 15 mL of water, 15 mL of 1 N NaOH and 5 mL of brine. The organic solution was concentrated and the residue was purified on a silica gel column (eluted with a gradient of 35-65% EtOAc in hexanes) to give methyl 2-(1-((tert-butoxycarbonyl)amino)ethyl)-5-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)-1H-pyrrole-3-carboxylate (326b) (6.3 g, 71% yield) as a yellow amorphous. 1H NMR (400 MHz, DMSO-d6) δ ppm 11.42 (1H, br.), 7.76 (1H, dd, J=7.4, 1.2 Hz), 7.63 (1H, dd, J=8.0, 1.2 Hz), 7.38 (2H, m), 7.03 (1H, d, J=7.8 Hz), 5.94 (1H, s), 5.44 (1H, m), 3.77 (3H, s), 2.56 (3H, s), 1.58 (9H, s), 1.40 (12H, m). m/z (ESI, +ve) 482.1 (M+H)+.

Provenance & Evidence