(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Cyanobenzoate (19)
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-cyanobenzoic 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 159 mg (75%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (d, J = 2.0 Hz, 1H), 8.64 (d, J = 8.1 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 8.09–8.14 (m, 2H), 7.99–8.05 (m, 2H), 7.66 (s, 1H), 7.37 (d, J = 1.5 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.99 (d, J = 8.3 Hz, 1H), 6.50 (d, J = 7.6 Hz, 1H), 5.17 (d, J = 2.8 Hz, 1H), 5.11–5.27 (m, 1H), 4.44–4.53 (m, 2H), 3.87 (s, 3H), 3.04–3.17 (m, 2H), 2.28–2.38 (m, 1H), 2.07–2.26 (m, 1H), 1.97–2.06 (m, 1H), 1.51–1.78 (m, 5H), 0.94 (d, J = 6.3 Hz, 3H), 0.89 (d, J = 6.3 Hz, 3H); MS (ESI+) for C32H35N5O7m/z 602.2 (M + H)+. Anal. calcd for C32H35N5O7·0.90 H2O: C, 62.21; H, 6.00; N, 11.33. Found: C, 62.23; H, 6.06; N, 11.58.