(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl Cyclopropanecarboxylate (14)
Following the procedure described for the preparation of (3S)-3-({N-[(4-methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl acetate but substituting cyclopropanecarboxylic acid and making noncritical variations provided a crude product. This material was purified by Biotage MPLC (25 M, 2.5–4.5% methanol/dichloromethane) to afford 82 mg (43%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.57 (d, J = 2.0 Hz, 1H), 8.56 (d, J = 7.8 Hz, 1H), 8.43 (d, J = 7.6 Hz, 1H), 7.63 (s, 1H), 7.36 (d, J = 1.5 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.97–7.02 (m, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.85 (d, 1H), 4.78–4.96 (m, 1H), 4.33–4.51 (m, 2H), 3.87 (s, 3H), 3.02–3.16 (m, 2H), 2.22–2.35 (m, 1H), 2.01–2.11 (m, 1H), 1.89–2.00 (m, 1H), 1.65–1.77 (m, 3H), 1.46–1.65 (m, 3H), 0.81–0.98 (m, 10 H); MS (ESI+) for C28H36N4O7m/z 541.2 (M + H)+. Anal. calcd for C28H36N4O7·0.59 H2O: C, 61.01; H, 6.80; N, 10.16. Found: C, 61.04; H, 6.72; N, 10.00.