(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Methoxybenzoate (17)
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 4-methoxybenzoic 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 145 mg (68%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.59 (d, J = 1.8 Hz, 1H), 8.62 (d, J = 7.8 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 7.93 (d, J = 9.1 Hz, 2H), 7.65 (s, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.04–7.11 (m, 2H), 7.00 (dd, J = 8.6, 3.0 Hz, 2H), 6.50 (d, J = 7.6 Hz, 1H), 5.07 (s, 1H), 5.01–5.18 (m, 1H), 4.44–4.51 (m, 2H), 3.87 (s, 3H), 3.83 (s, 3H), 3.04–3.17 (m, 2H), 2.28–2.38 (m, 1H), 2.07–2.25 (m, 1H), 1.97–2.06 (m, 1H), 1.50–1.79 (m, 5H), 0.94 (d, J = 6.3 Hz, 3H), 0.89 (d, J = 6.3 Hz, 3H); MS (ESI+) for C32H38N4O8m/z 607.2 (M + H)+. Anal. calcd for C32H38N4O8·0.80 H2O·0.05 DCM: C, 61.56; H, 6.40; N, 8.96. Found: C, 61.84; H, 6.36; N, 8.58.