Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting Boc-(β t-butyl)-Ala-OH and making noncritical variations provided a golden syrup. This material was purified by Biotage MPLC (65i column, 2.5–3.5% methanol/chloroform) to afford 3.41 g (40%) of the title compound as a white foam. 1H NMR (DMSO-d6) δ 8.39 (d, J = 8 Hz, 1H), 7.64 (s, 1H), 7.00 (d, J = 8 Hz, 1H), 4.58 (d, J = 16 Hz, 1H), 4.52 (d, J = 16 Hz, 1H), 4.38 (m, 1H), 3.92 (m, 1H), 3.15 (t, J = 8 Hz, 1H), 3.07 (q, J = 8 Hz, 1H), 2.22 (m, 1H), 2.09 (m, 1H), 1.97 (m, 1H), 1.62 (m, 2H), 1.50 (m, 2H), 1.36 (s, 9H), 0.88 (s, 9H); MS (ESI+) for C20H34ClN3O6m/z 432.1 (M + H)+.