(2S)-2-((3S)-3-{[(Benzyloxy)carbonyl]amino}-2-oxopyrrolidin-1-yl)propanoic acid (84.5 g) was dissolved in DMF (2I) and O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate (161 g) was added, followed by N,N-diisopropylethylamine (92 ml) and morpholine (46 ml). The mixture was stirred under nitrogen for 2.5 h, and saturated aqueous ammonium chloride was added. The mixture was stirred for 15 min then partitioned between water and ethyl acetate. The separated organic phase was washed with lithium chloride (10% by weight), followed by saturated sodium bicarbonate and brine. The organic layer was dried (over sodium sulphate) and concentrated under reduced pressure to give the title compound (65 g) as a yellow solid.
