(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Fluorobenzoate (20)
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-fluorobenzoic 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 136 mg (65%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (d, J = 2.0 Hz, 1H), 8.63 (d, J = 7.8 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 8.04 (dd, J = 8.6, 5.6 Hz, 2H), 7.65 (s, 1H), 7.35–7.41 (m, 3H), 7.08 (t, J = 8.0 Hz, 1H), 6.99 (d, J = 8.1 Hz, 1H), 6.50 (d, J = 7.6 Hz, 1H), 5.12 (d, J = 1.3 Hz, 1H), 5.06–5.23 (m, 1H), 4.44–4.52 (m, 2H), 3.87 (s, 3H), 3.04–3.17 (m, 2H), 2.28–2.38 (m, 1H), 2.07–2.26 (m, 1H), 1.98–2.06 (m, 1H), 1.52–1.79 (m, 5H), 0.94 (d, J = 6.3 Hz, 3H), 0.89 (d, J = 6.3 Hz, 3H); MS (ESI+) for C31H35FN4O7m/z 595.2 (M + H)+. Anal. calcd for C31H35FN4O7·0.59 H2O·0.06 DCM: C, 61.28; H, 5.98; N, 9.20. Found: C, 61.27; H, 5.98; N, 9.11.