(3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dimethoxybenzoate (27)
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 2,6-dimethoxybenzoic acid and making noncritical variations provided a crude brown foam. This material was purified by Biotage MPLC (25 M, 3–4% methanol/dichloromethane) to afford 169 mg (66%) of the title compound as an off-white solid. 1H NMR (DMSO-d6) δ 11.58 (d, J = 2 Hz, 1H), 8.55 (d, J = 8 Hz, 1H), 8.45 (d, J = 8 Hz, 1H), 7.64 (s, 1H), 7.40–7.35 (m, 2H), 7.08 (t, J = 8 Hz, 1H), 7.00 (d, J = 8 Hz, 1H), 6.71 (d, J = 8 Hz, 1H), 6.50 (d, J = 8 Hz, 1H), 5.01 (d, J = 16 Hz, 1H), 4.95 (d, J = 16 Hz, 1H), 4.53–4.48 (m, 2H), 3.87 (s, 3H), 3.75 (s, 6H), 3.08 (m, 2H), 2.31 (m, 1H), 2.11–1.90 (m, 2H), 1.75–1.55 (m, 5H), 0.94 (d, J = 8 Hz, 3H), 0.89 (d, J = 8 Hz, 3H); MS (ESI+) for C33H40N4O9m/z 637.2 (M + H)+; anal. calcd for C33H40N4O9·0.25 H2O·0.25 CHCl3: C, 59.51; H, 6.12; N, 8.35. Found: C, 59.49; H, 6.08; N, 8.42.