To a solution of (R)-3-amino-1-morpholino-4-(phenylthio)butan-1-one (INTERMEDIATE 72, 375.5 mg, 1.34 mmol) in DMF (2.5 ml) and DIPEA (1.20 Ml, 6.87 mmol) was added 4-fluoro-3-nitrobenzenesulfonamide (INTERMEDIATE 18, 325.8 mg, 1.48 mmol), and the resulting dark solution was stirred at 50° C. overnight, under a nitrogen atmosphere. The mixture was diluted with EtOAc (50 ml) and washed with water and brine (30 ml each), dried (Na2SO4), filtered, and evaporated under reduced pressure. The concentrate was purified by column chromatography (ISCO, 40 g silica gel column, eluting with 0→100% EtOAc/DCM) to give the title product (532.5 mg, yield: 83%).
