5 (d, J = 8 Hz, 3H), 0.9 (d, J = 8 Hz, 3H); MS (ESI+) for C24H31ClN4O5m/z 491.1 (M + H)+; HRMS (ESI+) calcd for C24H31ClN4O5+H1 491.2056, found 491.2058.

(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl Acetate (13)
An oven-dried 40 mL scintillation vial with a spinbar was charged with acetic acid (27 mg, 0.46 mmol) followed by a solution of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-meth