(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl Benzoate (16)
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 benzoic 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 183 mg (91%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.59 (s, 1H), 8.64 (d, J = 8.1 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 7.98 (d, J = 8.1 Hz, 2H), 7.91–7.95 (m, 1H), 7.66–7.71 (m, 1H), 7.66 (s, 1H), 7.52–7.57 (m, 1H), 7.37 (d, J = 1.8 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.96–7.02 (m, 1H), 6.49 (d, J = 7.6 Hz, 1H), 5.13 (s, 1H), 5.06–5.24 (m, 1H), 4.44–4.53 (m, 2H), 3.87 (s, 3H), 3.04–3.15 (m, 2H), 2.34 (m, 1H), 2.07–2.27 (m, 1H), 1.98–2.07 (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 C31H36N4O7m/z 577.2 (M + H)+. Anal. calcd for C31H36N4O7·1.04 H2O: C, 62.54; H, 6.45; N, 9.41. Found: C, 62.49; H, 6.54; N, 9.31.