m, 4H), 1.67–1.53 (m, 4H), 0.88 (s, 9H); MS (ESI+) for C21H35N3O6m/z 426 (M + H). HRMS (ESI+) calcd for C21H35N3O6+H1 426.2599, found 426.2604.

4-Methoxy-N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-1H-indole-2-carboxamide (48)
A solution of N-((1S)-1-{[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide (185 mg, 0.39 mmol), iodomethane (0.12 mL, 2.0 mmol), and silver(I