Experimental Section General Procedures Unless otherwise noted, materials were obtained from commercial suppliers and used without further purification. The removal of solvent under reduced pressure or concentration refers to distillation using a Büchi rotary evaporator attached to a vacuum pump (3 mmHg). Products obtained as solids or high-boiling oils were dried under vacuum (1 mmHg). Silica gel chromatography was performed on either a CombiFlash (Teledyne ISCO), SP4, or Isolera (Biotage) purification system. All reactions were performed under a positive pressure of nitrogen or argon or with a drying tube at an ambient temperature (unless otherwise stated) in anhydrous solvents, unless otherwise indicated. Analytical thin-layer chromatography (TLC) was performed on glass-backed silica gel 60 F254 plates (Analtech, 0.25 mm), eluting with the appropriate solvent ratio (v/v). The reactions were assayed by high-performance liquid chromatography–mass spectrometry (LCMS) or TLC and terminated as judged by the consumption of the starting material. LCMS utilized wavelengths of 254 and 220 nm and either electrospray ionization (ESI) in positive mode or atmospheric-pressure chemical ionization (APCI) in positive mode. The TLC plates were visualized using UV light, p-anisaldehyde, phosphomolybdic acid, or iodine staining. Microwave-assisted reactions were run in a Biotage Initiator. 1H NMR spectra were recorded on a Bruker XWIN-NMR (400 MHz) spectrometer. Proton chemical shifts are reported in parts per million downfield from tetramethylsilane (TMS). 1H NMR data are reported as chemical shift (multiplicity, coupling constant, integration). Multiplicities are denoted as follows: s, singlet; d, doublet; t, triplet; q, quartet; dd, doublet of doublets; dt, doublet of triplets; and brs, broad singlet. For spectra obtained in CDCl3, DMSO-d6, and CD3OD, the residual protons (7.27, 2.50, and 3.31 ppm, respectively) were used as the internal references. The purity of the final products is >95% as determined by HPLC and/or 1H NMR analyses. N-(tert-Butoxycarbonyl)-3-[(3S)-2-oxopyrrolidin-3-yl]-l-alanine (6) A 3 L multineck flask equipped with an overhead stirrer and internal thermometer was charged with methyl N-(tert-butoxycarbonyl)-3-[(3S)-2-oxopyrrolidin-3-yl]-l-alaninate (compound 5)33 (205 g, 716 mmol) followed by methanol (1 L), and the solution was cooled to 0 °C using ice/NaCl bath. NaOH (115 g in 950 mL water, 2.9 mol) solution was precooled to 0 °C and then added to the flask via a pressure-equalizing dropping funnel at such a rate to maintain the internal temperature below 5 °C. The resulting solution was stirred at 0 °C for 1 h before neutralizing with conc. hydrochloric acid (keeping the internal temperature below 10 °C) and then removing the methanol in vacuo. The residue was diluted with ethyl acetate (400 mL), acidified to pH 3 with conc. hydrochloric acid, and then the mixture was transferred to a sep funnel, and the organics were removed. The aqueous was extracted with ethyl acetate (2 × 400 mL), and the combined organics were washed with brine, dried over MgSO4, filtered, and concentrated to yield the title compound as a white foam, 95%. 1H NMR (400 MHz, MeOD) δ 3.98–4.28 (m, 1H), 3.25–3.41 (m, 2H), 2.44–2.57 (m, 1H), 2.29–2.41 (m, 1H), 2.03–2.14 (m, 1H), 1.73–1.90 (m, 2H), 1.44 (s, 9H); MS (APCI−) for C12H20N2O5m/z 272.3 (M – H)−. tert-Butyl ((1S)-3-Diazo-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (7) A solution of N-(tert-butoxycarbonyl)-3-[(3S)-2-oxopyrrolidin-3-yl]-l-alanine (2.72 g, 10.0 mmol) in THF (100 mL) was placed under an atmosphere of N2 and cooled to −23 °C. The resulting clear colorless solution was successively treated with triethylamine (2.1 mL, 15.0 mmol) followed by isobutylchloroformate (1.6 mL, 12.0 mmol). The reaction mixture gradually became opaque with a fine white precipitate and after 1 h was filtered. The colorless filtrate was transferred to a nonground joint flask, cooled to 0 °C, and slowly treated with a solution of diazomethane (∼35 mL, ∼16.6 mmol) in diethyl ether. Note: The diazomethane was generated employing a Diazald kit according to the procedure described in the Aldrich Technical Bulletin AL-180. The resulting yellow clear solution was gradually warmed to room temperature (RT) over 16 h. At this time, N2 was bubbled through the reaction to remove excess diazomethane followed by in vacuo concentration. The resulting residue was diluted with ethyl acetate (100 mL), washed once with sat. NaHCO3 (50 mL), once with brine (50 mL), dried over MgSO4, filtered, and concentrated to give a crude yellow foam. This material was purified by LC (150 g 230–400 SiO2, 3–4% methanol/chloroform) to afford 2.72 g (92%) of the title compound as a light yellow foam. 1H NMR (DMSO-d6) δ 7.63 (bs, 1H), 7.42 (d, J = 8 Hz, 1H), 6.06 (bs, 1H), 3.96 (m, 1H), 3.13 (m, 2H), 2.21 (m, 1H), 2.01 (m, 1H), 1.86 (m, 1H), 1.63–1.52 (m, 2H), 1.38 (s, 9H); MS (ESI+) for C13H20N4O4m/z 319.0 (M + Na)+. tert-Butyl ((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (8) A three-neck flame-dried flask equipped with a nitrogen inlet and internal thermometer was charged with methyl N-(tert-butoxycarbonyl)-3-[(3S)-2-oxopyrrolidin-3-yl]-l-alaninate (10 g, 35 mmol), THF (200 mL), and chloroiodomethane (10.2 mL, 140 mmol), and the solution was cooled to −77 °C. LDA (140 mL, 210 mmol, 1.5 M mono-THF complex in cyclohexane) was added via a pressure-equalizing dropping funnel at such a rate to keep the internal temperature below −70 °C. After complete addition, the reaction was stirred for an additional hour and quenched with a mixture of AcOH (33 mL) and THF (200 mL) with a rate of addition regulated to maintain the internal temperature below −65 °C. After complete addition, the dark suspension was stirred for 10 min and then warmed to an ambient temperature. The reaction was diluted with ethyl acetate (500 mL), and the organics were washed with water (250 mL), satd. NaHCO3 (250 mL), and brine (250 mL), dried over MgSO4, filtered, and the solvents were removed in vacuo to yield the crude product as a dark oil, which was purified by flash chromatography eluting with ethyl acetate. The resulting solid was triturated with diethyl ether to afford the title compound as a pale yellow solid, 5.7 g, 54%. 1H NMR (400 MHz, DMSO-d6) δ 7.88 (s, 1H), 7.75 (d, J = 7.6 Hz, 1H), 4.73–4.94 (m, 2H), 4.37 (m, 1H), 3.28–3.43 (m, 2H), 2.46 (m, 1H), 2.30–2.40 (m, 1H), 2.02–2.14 (m, 1H), 1.77–1.95 (m, 2H), 1.60 (s, 9H); MS (API-ES+) for C13H21N2O4Cl m/z 327.1 (M + Na)+; anal. calcd for C13H21ClN2O4: C, 51.23; H, 6.95; N, 9.19. Found: C, 51.03; H, 6.93; N, 9.03. tert-Butyl((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (9) To a 3 L multinecked flask equipped with an overhead stirrer, nitrogen inlet, and internal thermometer was charged N-(tert-butoxycarbonyl)-3-[(3S)-2-oxopyrrolidin-3-yl]-l-alanine (190 g, 698 mmol) followed by dichloromethane (1100 mL) and the solution was cooled to 0 °C employing an ice/NaCl bath. N,O-Dimethylhydroxylamine hydrochloric acid salt (68 g, 698 mmol) was added followed by N-methylmorpholine (230 mL, 2.09 mol), HOBt.hydrate (106 g, 698 mmol), and EDCI (147 g, 768 mmol), and the mixture was stirred at 0 °C under nitrogen for 6 h before quenching with water (500 mL). The biphasic mixture was transferred to a sep funnel, and the organics were isolated, washed with 1 M hydrochloric acid (2 × 500 mL), water (400 mL), satd. NaHCO3 (2 × 700 mL), and brine (300 mL) and then dried over MgSO4, filtered, and the solvents were evaporated in vacuo to yield tert-butyl ((1S)-2-[methoxy(methyl)amino]-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}ethyl)carbamate as a pale yellow solid, 173 g, 79%. 1H NMR (400 MHz, CDCl3) δ 5.92 (s, 1H), 5.39 (d, J = 8.8 Hz, 1H), 4.66 (td, J = 9.6, 2.8 Hz, 1H), 3.77 (s, 3H), 3.33 (dd, J = 9.3, 4.0 Hz, 2H), 3.19 (s, 2H), 2.41–2.62 (m, 2H), 2.05–2.16 (m, 1H), 1.75–1.95 (m, 1H), 1.67 (m, 1H), 1.41 (s, 9H). To a 100 mL multinecked flask equipped with a stirrer bar, nitrogen inlet, and internal thermometer were charged magnesium turnings (dried in oven at 100 °C overnight, 1.04 g, 43 mmol) and HgCl2 (774 mg, 2.85 mmol), and the flask was purged with nitrogen for 10 min. THF (50 mL) was added, and the suspension was cooled to −45 °C before adding BOM-Cl (5.94 mL, 43 mmol), and the resulting suspension was stirred for 5 h, the temperature returning to 5 °C. The suspension was recooled to −50 °C, and tert-butyl ((1S)-2-[methoxy(methyl)amino]-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}ethyl)carbamate (1.5 g, 4.76 mmol) was added, and the thick suspension was stirred for 48 h under nitrogen and was allowed to come to an ambient temperature. The reaction was quenched by the careful addition of satd. NH4Cl solution (25 mL), and the mixture was stirred until effervescence ceased and then extracted with ethyl acetate (3 × 120 mL). The combined organics were dried over MgSO4, filtered, and the solvents were evaporated in vacuo to yield a crude orange gum, which was purified by flash chromatography, eluting with 1–3% methanol/dichloromethane to afford the title compound as a clear glass, 900 mg, 50%. 1H NMR (400 MHz, CDCl3) δ 7.21–7.33 (m, 5H), 5.63–5.73 (m, 2H), 4.52 (m, 3H), 4.19 (q, J = 17.4 Hz, 2H), 3.19–3.25 (m, 2H), 2.29–2.42 (m, 2H), 1.68–1.93 (m, 3H), 1.35 (s, 9H); MS (APCI+) for C20H28N2O5m/z 378.1 (M + H)+. (3S)-3-[(2S)-2-Amino-4-chloro-3-oxobutyl]pyrrolidin-2-one, Hydrochloride Salt (10) A solution of tert-butyl ((1S)-3-diazo-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl) carbamate (592 mg, 2.0 mmol) in 1,4-dioxane (7 mL) was placed under an atmosphere of N2 and cooled to 0 °C. This clear pale yellow solution was dropwise treated with a solution of 4 M hydrochloric acid in 1,4-dioxane (5 mL, 20 mmol) with copious gas evolution observed. Upon complete addition, the reaction was warmed to RT over 1 h with the formation of a white precipitate. The solid was collected by filtration, washed with diethyl ether, and dried to give 401 mg (83%) of the title compound as a white powder. 1H NMR (DMSO-d6) δ 8.76 (bs, 3H), 7.96 (s, 1H), 4.93 (d, J = 16 Hz, 1H), 4.80 (d, J = 16 Hz, 1H), 4.28 (m, 1H), 3.18 (m, 2H), 2.61 (m, 1H), 2.30 (m, 1H), 1.93 (m, 2H), 1.70 (m, 1H); MS (ESI+) for C8H13ClN2O2m/z 205.0 (M + H)+. tert-Butyl ((1S)-3-Bromo-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (11) A solution of tert-butyl ((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (1.26 g, 4.3 mmol) in dichloromethane (107 mL) at 0 °C under nitrogen was treated with 48% hydrobromic acid (0.48 mL, 4.3 mmol) with effervescence observed. The reaction was stirred at 0 °C for 1 h, washed once with water (30 mL), dried over MgSO4, filtered, and concentrated to afford 1.23 g (83%) of the title compound as a white solid. 1H NMR (400 MHz, DMSO-d6) δ 7.64 (s, 1H), 7.51 (d, J = 8 Hz, 1H), 4.46 (d, J = 16 Hz, 1H), 4.41 (d, J = 16 Hz, 1H), 4.19 (m, 1H), 3.13 (m, 2H), 2.26 (m, 1H), 2.13 (m, 1H), 1.87 (m, 1H), 1.63 (m, 2H), 1.38 (s, 9H); MS (ESI+) for C13H21BrN2O4m/z 371.0 (M + H)+. N-((1S)-1-{[((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide (12) A solution of 29, N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide (244 mg, 0.59 mmol) in 1,4-dioxane (1.0 mL) was placed under an atmosphere of N2. This clear colorless solution was treated with a solution of 4 M hydrochloric acid in 1,4-dioxane with no observable change. The reaction gradually became opaque with the formation of a gummy precipitate. After 2 h, the volatiles were removed in vacuo, diluted with 1:1 ethanol/1,4-dioxane, concentrated, and high-vacuum-dried to give N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide hydrochloride as an off-white solid. 1H NMR (DMSO-d6) δ 9.18 (d, J = 8 Hz, 1H), 8.40 (bs, 3H), 7.69 (s, 1H), 4.68 (s, 2H), 4.49 (m, 1H), 3.81 (m, 1H), 3.15 (m, 2H), 2.37 (m, 1H), 2.17 (m, 1H), 1.92 (m, 1H), 1.67 (m, 3H), 1.55 (m, 2H), 0.92 (d, J = 4 Hz, 3H), 0.88 (d, J = 4 Hz, 3H); MS (ESI+) for C14H24ClN3O3m/z 318.1 (M + H)+. A solution of the crude hydrochloride salt and 4-methoxy-1H-indole-2-carboxylic acid (123 mg, 0.64 mmol) in DMF (2.5 mL) was placed under an atmosphere of N2 and cooled to 0 °C. This pale yellow solution was successively treated with HATU (245 mg, 0.64 mmol) and N-methylmorpholine (0.14 mL, 1.29 mmol) turning a brighter color. After 30 min, the reaction was quenched with 1:1 ice/sat NaHCO3 (25 mL) and extracted three times with ethyl acetate (20 mL). The combined organics were washed once with brine (30 mL), dried over MgSO4, filtered, and concentrated to give a yellow syrup. This material was purified by LC (30 g 230–400 SiO2, 4% methanol/chloroform) to afford 167 mg (58%) of the title compound as an off-white solid. 1H NMR (DMSO-d6) δ 11.59 (s, 1H), 8.62 (d, J = 8 Hz, 1H), 8.44 (d, J = 4 Hz, 1H), 7.65 (s, 1H), 7.38 (s, 1H), 7.10 (t, J = 8 Hz, 1H), 7.02 (d, J = 8 Hz, 1H), 6.51 (d, J = 8 Hz, 1H), 4.60 (d, J = 16 Hz, 1H), 4.58 (d, J = 16 Hz, 1H), 4.46 (m, 2H), 3.89 (s, 3H), 3.11 (m, 2H), 2.29 (m, 1H), 2.11 (m, 1H), 1.99 (m, 1H), 1.76–1.54 (m, 5H), 0.95 (d, J = 8 Hz, 3H), 0.9 (d, J = 8 Hz, 3H); MS (ESI+) for C24H31ClN4O5m/z 491.1 (M + H)+; HRMS (ESI+) calcd for C24H31ClN4O5+H1 491.2056, found 491.2058. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl Acetate (13) An oven-dried 40 mL scintillation vial with a spinbar was charged with acetic acid (27 mg, 0.46 mmol) followed by a solution of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide (172 mg, 0.35 mmol) in DMF (3.5 mL) and purged with N2. This pale yellow solution was then treated with CsF (122 mg, 0.81 mmol), sealed with a Teflon-lined screwcap, and heated at 65 °C on a reaction block with vigorous stirring. After 3 h, the reaction was cooled to RT, diluted with water (30 mL), and extracted with dichloromethane (4 × 7 mL). The combined organic layers were washed with water (2 × 20 mL), brine (20 mL), and concentrated in vacuo. This material was purified by Biotage MPLC (25 M, 2.5–4.5% methanol/dichloromethane) to afford 78 mg (45%) of the title compound as a white solid. 1H NMR (400 MHz, DMSO-d6) δ 11.57 (s, 1H), 8.57 (d, J = 7.8 Hz, 1H), 8.43 (d, J = 7.6 Hz, 1H), 7.64 (s, 1H), 7.36 (d, J = 1.8 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.99 (d, J = 8.1 Hz, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.83 (d, J = 3.0 Hz, 1H), 4.76–4.95 (m, 1H), 4.35–4.50 (m, 2H), 3.87 (s, 3H), 3.03–3.17 (m, 2H), 2.22–2.35 (m, 1H), 2.09–2.22 (m, 1H), 2.07 (s, 3H), 1.90–2.04 (m, 1H), 1.65–1.77 (m, 2H), 1.48–1.65 (m, 3H), 0.94 (d, J = 6.3 Hz, 3H), 0.89 (d, J = 6.3 Hz, 3H); MS (ESI+) for C26H34N4O7m/z 515.2 (M + H)+. Anal. calcd for C26H34N4O7·0.65 H2O: C, 59.34; H, 6.76; N, 10.65. Found: C, 59.41; H, 6.63; N, 10.68. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl Cyclopropanecarboxylate (14) 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 cyclopropanecarboxylic 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 82 mg (43%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.57 (d, J = 2.0 Hz, 1H), 8.56 (d, J = 7.8 Hz, 1H), 8.43 (d, J = 7.6 Hz, 1H), 7.63 (s, 1H), 7.36 (d, J = 1.5 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.97–7.02 (m, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.85 (d, 1H), 4.78–4.96 (m, 1H), 4.33–4.51 (m, 2H), 3.87 (s, 3H), 3.02–3.16 (m, 2H), 2.22–2.35 (m, 1H), 2.01–2.11 (m, 1H), 1.89–2.00 (m, 1H), 1.65–1.77 (m, 3H), 1.46–1.65 (m, 3H), 0.81–0.98 (m, 10 H); MS (ESI+) for C28H36N4O7m/z 541.2 (M + H)+. Anal. calcd for C28H36N4O7·0.59 H2O: C, 61.01; H, 6.80; N, 10.16. Found: C, 61.04; H, 6.72; N, 10.00. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl Pivalate (15) 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 pivalic 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 152 mg (78%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (s, 1H), 8.56 (d, J = 7.8 Hz, 1H), 8.44 (d, J = 7.8 Hz, 1H), 7.64 (s, 1H), 7.36 (s, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.99 (d, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.84 (s, 1H), 4.77–4.94 (m, 1H), 4.34–4.51 (m, 2H), 3.87 (s, 3H), 3.02–3.16 (m, 2H), 1.91–2.36 (m, 3H), 1.48–1.78 (m, 5H), 1.16 (s, 9H), 0.94 (d, J = 6.3 Hz, 3H), 0.89 (d, J = 6.3 Hz, 3H); MS (ESI+) for C29H40N4O7m/z 557.2 (M + H)+. Anal. calcd for C29H40N4O7·0.76 H2O: C, 61.07; H, 7.34; N, 9.82. Found: C, 61.14; H, 7.63; N, 9.59. (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. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Methoxybenzoate (17) 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-methoxybenzoic 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 145 mg (68%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.59 (d, J = 1.8 Hz, 1H), 8.62 (d, J = 7.8 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 7.93 (d, J = 9.1 Hz, 2H), 7.65 (s, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.04–7.11 (m, 2H), 7.00 (dd, J = 8.6, 3.0 Hz, 2H), 6.50 (d, J = 7.6 Hz, 1H), 5.07 (s, 1H), 5.01–5.18 (m, 1H), 4.44–4.51 (m, 2H), 3.87 (s, 3H), 3.83 (s, 3H), 3.04–3.17 (m, 2H), 2.28–2.38 (m, 1H), 2.07–2.25 (m, 1H), 1.97–2.06 (m, 1H), 1.50–1.79 (m, 5H), 0.94 (d, J = 6.3 Hz, 3H), 0.89 (d, J = 6.3 Hz, 3H); MS (ESI+) for C32H38N4O8m/z 607.2 (M + H)+. Anal. calcd for C32H38N4O8·0.80 H2O·0.05 DCM: C, 61.56; H, 6.40; N, 8.96. Found: C, 61.84; H, 6.36; N, 8.58. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Methylbenzoate (18) 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-methylbenzoic 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 92 mg (44%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.59 (d, J = 1.8 Hz, 1H), 8.63 (d, J = 8.1 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 7.87 (d, J = 8.1 Hz, 2H), 7.65 (s, 1H), 7.37 (d, J = 1.8 Hz, 1H), 7.34 (d, J = 8.3 Hz, 2H), 7.08 (t, J = 8.0 Hz, 1H), 6.97–7.01 (m, 1H), 6.50 (d, J = 7.8 Hz, 1H), 5.09 (s, 1H), 5.03–5.20 (m, 1H), 4.43–4.52 (m, 2H), 3.87 (s, 3H), 3.04–3.17 (m, 2H), 2.38 (s, 3H), 2.28–2.34 (m, 1H), 2.06–2.14 (m, 1H), 1.96–2.06 (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 C32H38N4O7m/z 591.2 (M + H)+. Anal. calcd for C32H38N4O7·0.10 H2O·0.11 DCM: C, 64.08; H, 6.43; N, 9.31. Found: C, 64.36; H, 6.41; N, 8.92. (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. (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. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Chlorobenzoate (21) 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-chlorobenzoic 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 172 mg (80%) of the title compound. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (d, J = 1.8 Hz, 1H), 8.63 (d, J = 7.8 Hz, 1H), 8.46 (d, J = 7.6 Hz, 1H), 7.98 (d, J = 8.6 Hz, 2H), 7.65 (s, 1H), 7.62 (d, J = 8.6 Hz, 2H), 7.37 (d, J = 1.8 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), 5.13 (d, J = 1.5 Hz, 1H), 5.07–5.23 (m, 1H), 4.44–4.52 (m, 2H), 3.87 (s, 3H), 3.04–3.14 (m, 2H), 2.28–2.38 (m, 1H), 2.06–2.26 (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 C31H35ClN4O7m/z 611.1 (M + H)+. Anal. calcd for C31H35ClN4O7·0.72 H2O·0.05 DCM: C, 59.36; H, 5.86; N, 8.92. Found: C, 59.31; H, 5.99; N, 9.23. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate (22) 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-dichlorobenzoic acid and making noncritical variations provided a crude product. This material was purified by LC (20 g 230–400 SiO2, 3% methanol/chloroform) to afford 114 mg (65%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.57 (d, J = 2 Hz, 1H), 8.62 (d, J = 8 Hz, 1H), 8.46 (d, J = 4 Hz, 1H), 7.65–7.53 (m, 4H), 7.36 (s, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.19 (d, J = 20 Hz, 1H), 5.15 (d, J = 20 Hz, 1H), 4.51 (m, 2H), 3.87 (s, 3H), 3.11 (m, 2H), 2.30 (m, 1H), 2.06 (m, 2H), 1.76–1.51 (m, 5H), 0.94 (d, J = 8 Hz, 3H), 0.89 (d, J = 8 Hz, 3H); MS (ESI+) for C31H34Cl2N4O7m/z 645.1 (M + H)+; Anal. Calcd for C31H34Cl2N4O7·0.2 H2O: C, 57.36; H, 5.34; N, 8.63. Found: C, 57.23; H, 5.55; N, 8.46. HRMS (ESI+) calcd for C31H34Cl2N4O7+H1 645.1877, found 645.1871. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Difluorobenzoate (23) 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-difluorobenzoic acid and making noncritical variations provided a crude brown oily solid. This material was triturated with chloroform/ethyl acetate to afford 180 mg (75%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.65 (d, J = 2 Hz, 1H), 8.68 (d, J = 8 Hz, 1H), 8.54 (d, J = 8 Hz, 1H), 7.73–7.65 (m, 2H), 7.36 (s, 1H), 7.27 (t, J = 8 Hz, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.19 (d, J = 16 Hz, 1H), 5.14 (d, J = 16 Hz, 1H), 4.48 (m, 2H), 3.87 (s, 3H), 3.11 (m, 2H), 2.32 (m, 1H), 2.11–1.91 (m, 2H), 1.81–1.56 (m, 5H), 0.94 (d, J = 4 Hz, 3H), 0.89 (d, J = 4 Hz, 3H); MS (ESI+) for C31H34F2N4O7m/z 613.2 (M + H)+; HRMS (ESI+) calcd for C31H34F2N4O7+H1 613.2469, found 613.2476. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Chloro-2-hydroxybenzoate (24) 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-chlorosalicylic acid and making noncritical variations provided a crude brown syrup. This material was purified by Biotage MPLC (25 M, 2–3% methanol/dichloromethane) to afford 64 mg (25%) of the title compound as a tan solid. 1H NMR (DMSO-d6) δ 11.58 (s, 1H), 10.50 (bs, 1H), 8.65 (d, J = 8 Hz, 1H), 8.46 (d, J = 8 Hz, 1H), 7.81 (d, J = 8 Hz, 1H), 7.63 (m, 1H), 7.37 (s, 1H), 7.08 (m, 2H), 7.00 (m, 2H), 6.50 (d, J = 8 Hz, 1H), 5.16 (d, J = 16 Hz, 2H), 5.11 (d, J = 16 Hz, 2H), 4.49 (m, 2H), 3.87 (s, 3H), 3.13 (m, 2H), 2.32 (m, 1H), 2.11–1.98 (m, 2H), 1.76–1.55 (m, 5H), 0.94 (d, J = 6 Hz, 3H), 0.89 (d, J = 6 Hz, 3H); MS (ESI-) for C31H35ClN4O8m/z 625.1 (M – H)−; anal. calcd for C31H35ClN4O8·0.1 H2O·0.14 CHCl3: C, 57.93; H, 5.52; N, 8.68. Found: C, 58.04; H, 5.78; N, 8.74; HRMS (ESI+) calcd for C31H35ClN4O8+H1 627.2216, found 627.2219. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 4-Cyano-2-fluorobenzoate (25) 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-cyano-2-fluorobenzoic acid and making noncritical variations provided a crude oily brown solid. This material was purified by Biotage MPLC (25 M, 2.5–3.5% methanol/dichloromethane) to afford 119 mg (48%) of the title compound as an off-white powder. 1H NMR (DMSO-d6) δ 11.58 (d, J = 2 Hz, 1H), 8.63 (d, J = 8 Hz, 1H), 8.46 (d, J = 8 Hz, 1H), 8.06 (m, 2H), 7.83 (d, J = 8 Hz, 1H), 7.65 (s, 1H), 7.36 (d, J = 2 Hz, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.50 (d, J = 8 Hz, 1H), 5.16 (d, J = 16 Hz, 1H), 5.11 (d, J = 16 Hz, 1H), 4.49 (m, 2H), 3.87 (s, 3H), 3.11 (m, 2H), 2.32 (m, 1H), 2.10–1.98 (m, 2H), 1.77–1.53 (m, 5H), 0.94 (d, J = 6 Hz, 3H), 0.89 (d, J = 6 Hz, 3H); MS (ESI+) for C32H34FN5O7m/z 620.1 (M + H)+; anal. calcd for C32H34FN5O7·0.3 H2O: C, 61.49; H, 5.58; N, 11.20. Found: C, 61.47; H, 5.61; N, 10.98; HRMS (ESI+) calcd for C32H34FN5O7+H1 620.2515, found 620.2532. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dimethylbenzoate (26) 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-dimethylbenzoic 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 177 mg (73%) of the title compound as an off-white glass. 1H NMR (DMSO-d6) δ 11.58 (d, J = 2 Hz, 1H), 8.63 (d, J = 8 Hz, 1H), 8.46 (d, J = 8 Hz, 1H), 7.65 (s, 1H), 7.36 (s, 1H), 7.25 (t, J = 8 Hz, 1H), 7.08 (m, 3H), 7.00 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.11 (s, 2H), 4.51 (m, 2H), 3.87 (s, 3H), 3.10 (m, 2H), 2.32–2.21 (m, 7H), 2.07 (m, 2H), 1.78–1.53 (m, 5H), 0.94 (d, J = 8 Hz, 3H), 0.89 (d, J = 8 Hz, 3H); MS (ESI+) for C33H40N4O7m/z 605.2 (M + H)+; anal. calcd for C33H40N4O7·0.3 H2O·0.2 CHCl3: C, 62.90; H, 6.49; N, 8.84. Found: C, 62.95; H, 6.42; N, 8.72. HRMS (ESI+) calcd for C33H40N4O7+H1 605.2970, found 605.2985. (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. (3S)-3-({N-[(4-Methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2-Cyanobenzoate (28) 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-cyanobenzoic acid and making noncritical variations provided a crude brown oily solid. This material was triturated with chloroform/ethyl acetate to afford 91 mg (38%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.58 (s, 1H), 8.65 (d, J = 8 Hz, 1H), 8.46 (d, J = 8 Hz, 1H), 8.17 (m, 1H), 8.04 (m, 1H), 7.88 (m, 1H), 7.65 (s, 1H), 7.37 (s, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.19 (m, 2H), 4.50 (m, 2H), 3.87 (s, 3H), 3.11 (m, 2H), 2.32 (m, 1H), 2.07–1.97 (m, 2H), 1.76–1.56 (m, 5H), 0.94 (d, J = 6 Hz, 3H), 0.89 (d, J = 6 Hz, 3H); MS (ESI+) for C32H35N5O7m/z 602.2 (M + H)+; anal. calcd for C32H35N5O7·0.4 H2O: C, 63.12, H, 5.93; N, 11.50. Found: C, 63.16; H, 5.96; N, 11.43; HRMS (ESI+) calcd for C32H35N5O7+H1 602.2609, found 602.2610. (3S)-3-[(tert-Butoxycarbonyl)amino]-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate A solution of tert-butyl ((1S)-3-bromo-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (1.17 g, 3.2 mmol) in DMF (16 mL) was treated with 2,6-dichlorobenzoic acid (794 mg, 4.2 mmol) followed by cesium fluoride (1.18 g, 7.4 mmol). The resulting suspension was placed in a preheated oil bath at 65 °C for 2 h. The reaction was cooled to an ambient temperature, diluted with ethyl acetate (100 mL), washed once with water (40 mL) and with brine (40 mL), dried over MgSO4, filtered, and concentrated to give a crude yellow syrup. This material was purified by Biotage MPLC (25 M, 4.5% methanol/dichloromethane) to afford 1.19 mg (80%) of the title compound as an off-white glass. 1H NMR (400 MHz, DMSO-d6) δ 7.60 (m, 5H), 5.35 (s, 2H), 4.32 (m, 1H), 3.23 (m, 2H), 2.24 (m, 1H), 2.11 (m, 1H), 1.86 (m, 1H), 1.67 (m, 2H), 1.35 (s, 9H); MS (ESI+) for C20H24Cl2N2O6m/z 481.0 (M + Na)+; HRMS (ESI+) calcd for C20H24Cl2N2O6+H 481.0903, found 481.0890. N2-(tert-Butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide A solution of (3S)-3-[(2S)-2-amino-4-chloro-3-oxobutyl]pyrrolidin-2-one hydrochloride (391 mg, 1.6 mmol) and Boc-Leu-OH (412 mg, 1.8 mmol) in DMF (9 mL) was placed under an atmosphere of N2 and cooled to 0 °C. This clear pale yellow solution was successively treated with HATU (678 mg, 1.8 mmol) followed by N-methylmorpholine (0.41 mL, 3.7 mmol). The reaction mixture gradually became opaque and after 1 h was quenched with 1:1 ice/sat aqueous NaHCO3 (40 mL) and extracted three times with ethyl acetate (40 mL). The combined organics were washed once with brine (30 mL), dried over MgSO4, filtered, and concentrated to give a yellow syrup. This material was purified by LC (50 g 230–400 SiO2, 3–5% methanol/chloroform) to afford 636 mg (40%) of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide as a white foam. 1H NMR (DMSO-d6) δ 8.47 (d, J = 8 Hz, 1H), 7.64 (s, 1H), 7.04 (d, J = 8 Hz, 1H), 4.60 (d, J = 16 Hz, 1H), 4.53 (d, J = 16 Hz, 1H), 4.40 (m, 1H), 3.90 (m, 1H), 3.16 (m, 1H), 3.08 (m, 1H), 2.24 (m, 1H), 2.10 (m, 1H), 1.98 (m, 1H), 1.63 (m, 2H), 1.45–1.37 (m, 11 H), 0.89 (d, J = 4 Hz, 3H), 0.85 (d, J = 4 Hz, 3H); MS (ESI+) for C19H32ClN3O5m/z 418.1 (M + H)+. Anal. calcd for C19H32ClN3O5·0.6 H2O: C, 53.22; H, 7.81; N, 9.80. Found: C, 53.00; H, 7.65; N, 9.54. HRMS (ESI+) calcd for C19H32ClN3O5+H1 418.2103, found 418.2091. (3S)-3-{[N-(tert-Butoxycarbonyl)-l-leucyl]amino}-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate (29) Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting (3S)-3-[(tert-butoxycarbonyl)amino]-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-dichlorobenzoate and making noncritical variations provided a brown foam. This material was purified by LC (50 g 230–400 SiO2, 2.5–3.5% methanol/chloroform) to afford 413 mg (61%) of the title compound as a light yellow foam. 1H NMR (DMSO-d6) δ 8.47 (d, J = 8 Hz, 1H), 7.60 (m, 4H), 7.05 (d, J = 8 Hz, 1H), 5.19 (d, J = 16 Hz, 1H), 5.13 (d, J = 16 Hz, 1H), 4.47 (m, 1H), 3.95 (m, 1H), 3.16 (m, 1H), 3.08 (m, 1H), 2.27 (m, 1H), 2.10 (m, 1H), 2.03 (m, 1H), 1.65 (m, 2H), 1.47–1.37 (m, 11 H), 0.89 (d, J = 4 Hz, 3H), 0.85 (d, J = 4 Hz, 3H); MS (ESI+) for C26H35Cl2N3O7m/z 572.1 (M + H)+. Anal. calcd for C26H35Cl2N3O7·0.5 H2O: C, 53.70; H, 6.24; N, 7.23. Found: C, 53.74; H, 6.31; N, 7.31; HRMS (ESI+) calcd for C26H35Cl2N3O7+Na 594.1744, found 594.1729. (3S)-3-[(N-Acetyl-l-leucyl)amino]-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate (30) Following the procedure described for the preparation of N2-acetyl-N1-[(1S)-1-(chloroacetyl)-4-(dimethylamino)-4-oxobutyl]-N2-methyl-l-leucinamide but substituting (3S)-3-{[N-(tert-butoxycarbonyl)-l-leucyl]amino}-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-dichlorobenzoate and making noncritical variations provided a pale yellow oil. This material was purified by Biotage MPLC (25 M, 3.5–4.5% methanol/dichloromethane) to afford 161 mg (78%) of the title compound as a white foam. 1H NMR (DMSO-d6) δ 8.56 (d, J = 8 Hz, 1H), 8.06 (d, J = 8 Hz, 1H), 7.65–7.53 (m, 4H), 5.17 (d, J = 16 Hz, 1H), 5.10 (d, J = 16 Hz, 1H), 4.44 (m, 1H), 4.25 (m, 1H), 3.12 (m, 2H), 2.25 (m, 1H), 2.06 (m, 1H), 1.97 (m, 1H), 1.84 (s, 3H), 1.63 (m, 3H), 1.45 (m, 2H), 0.90 (d, J = 8 Hz, 3H), 0.85 (d, J = 8 Hz, 3H); MS (ESI+) for C23H29Cl2N3O6m/z 514.0 (M + H)+; anal. calcd for C23H29Cl2N3O6·0.25 H2O·0.1 EtOAc: C, 53.26; H, 5.79; N, 7.96. Found: C, 53.27; H, 5.82; N, 7.84. HRMS (ESI+) calcd for C23H29Cl2N3O6+H1 514.1506, found 514.1508. (3S)-3-{[N-(1H-Benzimidazol-2-ylcarbonyl)-l-leucyl]amino}-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate (31) Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting (3S)-3-{[N-(tert-butoxycarbonyl)-l-leucyl]amino}-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-dichlorobenzoate and 1H-benzimidazole-2-carboxylic acid and making noncritical variations provided a crude yellow oil. This material was purified by Biotage MPLC (25 M, 3–4% methanol/dichloromethane) to afford 95 mg (72%) of the title compound as an off-white foam. 1H NMR (DMSO-d6) δ 13.32 (s, 1H), 8.89 (d, J = 8 Hz, 1H), 8.60 (d, J = 8 Hz, 1H), 7.74 (d, J = 8 Hz, 1H), 7.59 (m, 5H), 7.29 (m, 2H), 5.20 (d, J = 20 Hz, 1H), 5.15 (d, J = 20 Hz, 1H), 4.56 (m, 2H), 3.12 (m, 2H), 2.30 (m, 1H), 2.01 (m, 2H), 1.83 (m, 1H), 1.65 (m, 4H), 0.92 (d, J = 8 Hz, 3H), 0.89 (d, J = 8 Hz, 3H); MS (ESI+) for C29H31Cl2N5O6m/z 616.0 (M + H)+. Anal. calcd for C29H31Cl2N5O6: C, 56.50; H, 5.07; N, 11.36. Found: C, 57.28; H, 5.32; N, 11.35. HRMS (ESI+) calcd for C29H31Cl2N5O6+H1 616.1724, found 616.1729. (3S)-3-({4-Methyl-N-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate (3) 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 N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-N2-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucinamide and 2,6-dichlorobenzoic acid and making noncritical variations provided a light amber residue. The residue was purified by preparative HPLC (Luna 10μ C18) eluting with a gradient of MeCN containing 0.1% AcOH in water containing 0.1% AcOH to give 0.155 g (54%) of the title compound as a cream colored solid. 1H NMR (300 MHz, DMSO-d6) δ 8.52 (d, J = 8 Hz, 1H), 7.79 (d, J = 8 Hz, 1H), 7.71 (s, 1H), 7.66–7.55 (m, 3H), 5.18 (s, 2H), 4.54–4.40 (m, 1H), 4.37–4.35 (m, 1H), 4.25 (m, 1H), 3.98–3.91 (m, 1H), 3.84–3.72 (m, 1H), 3.23–3.07 (m, 2H), 2.33–2.23 (m, 1H), 2.16–2.05 (m, 2H), 1.86–1.74 (m, 3H), 1.72–1.62 (m, 5H), 0.89 (s, 9H); MS (ESI+) for C27H35Cl2N3O7m/z 584 (M + H). Anal. calcd for C27H35Cl2N3O7·0.5 H2O: C, 54.64; H, 6.11; N, 7.08. Found: C, 54.26; H, 6.00; N, 6.87. HRMS (ESI+) calcd for C27H35Cl2N3O7+H1 584.1925, found 584.1921. N2-(tert-Butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-l-leucinamide (32) Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting Boc-(β t-butyl)-Ala-OH and making noncritical variations provided a golden syrup. This material was purified by Biotage MPLC (65i column, 2.5–3.5% methanol/chloroform) to afford 3.41 g (40%) of the title compound as a white foam. 1H NMR (DMSO-d6) δ 8.39 (d, J = 8 Hz, 1H), 7.64 (s, 1H), 7.00 (d, J = 8 Hz, 1H), 4.58 (d, J = 16 Hz, 1H), 4.52 (d, J = 16 Hz, 1H), 4.38 (m, 1H), 3.92 (m, 1H), 3.15 (t, J = 8 Hz, 1H), 3.07 (q, J = 8 Hz, 1H), 2.22 (m, 1H), 2.09 (m, 1H), 1.97 (m, 1H), 1.62 (m, 2H), 1.50 (m, 2H), 1.36 (s, 9H), 0.88 (s, 9H); MS (ESI+) for C20H34ClN3O6m/z 432.1 (M + H)+. N1-((1S)-3-(Benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N2-(tert-butoxycarbonyl)-4-methyl-l-leucinamide (33) Following the procedure described for the preparation of tert-butyl [(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]carbamate but substituting Boc-(β t-butyl)-Ala-OH and making noncritical variations provided a brown syrup. This material was purified by LC (33 g 230–400 SiO2, 1–2.5% methanol/chloroform) to afford 258 mg (55%) of the title compound as a light yellow foam. 1H NMR (DMSO-d6) δ 8.23 (d, J = 8 Hz, 1H), 7.62 (s, 1H), 7.32 (m, 5H), 6.96 (d, J = 8 Hz, 1H), 4.46 (s, 2H), 4.35–4.33 (m, 2H), 4.21 (d, J = 16 Hz, 1H), 3.95 (m, 1H), 3.09 (m, 2H), 2.24 (m, 1H), 2.07 (m, 1H), 1.92 (m, 1H), 1.58 (m, 2H), 1.46 (m, 2H), 1.35 (s, 9H), 0.87 (m, 9H); MS (ESI+) for C27H41N3O6m/z 504.2 (M + H)+. N-((1S)-1-{[((1S)-3-(Benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-4-methoxy-1H-indole-2-carboxamide (34) Following the procedure described for the preparation of N-[(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]-4-methoxy-1H-indole-2-carboxamide but substituting N1-((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N2-(tert-butoxycarbonyl)-4-methyl-l-leucinamide and making noncritical variations provided a golden syrup. This material was purified by Biotage MPLC (25 M column, 3% methanol/chloroform) to afford 173 mg (60%) of the title compound as an off-white foam. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (s, 1H), 8.43 (app t, J = 8 Hz, 2H), 7.62 (s, 1H), 7.32 (m, 6H), 7.08 (t, J = 8 Hz, 1H), 7.00 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 4.52 (m, 1H), 4.47–4.35 (m, 4H), 4.22 (d, J = 16 Hz, 1H), 3.87 (s, 3H), 3.05 (m, 2H), 2.28 (m, 1H), 2.06 (m, 1H), 1.93 (m, 1H), 1.64–1.57 (m, 3H), 0.92 (s, 9H); MS (ESI+) for C32H40N4O6m/z 577.2 (M + H)+; anal. calcd for C32H40N4O6·0.33 methanol·0.25 H2O: C, 65.62; H, 7.13; N, 9.47. Found: C, 65.65; H, 6.90; N, 9.58; HRMS (ESI+) calcd for C32H40N4O6 577.3021, found 577.3001. N-((1S)-1-{[((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-4-methoxy-1H-indole-2-carboxamide (35) Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-l-leucinamide and making noncritical variations provided a pale yellow solid. This material was purified by Biotage MPLC (40 M column, 2–4.5% methanol/chloroform) to afford 920 g (60%) of the title compound as an off-white solid. 1H NMR (400 MHz, DMSO-d6) δ 11.59 (d, J = 1.8 Hz, 1H), 8.54 (d, J = 7.8 Hz, 1H), 8.45 (d, J = 8.1 Hz, 1H), 7.64 (s, 1H), 7.32 (d, J = 1.8 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 7.00 (d, J = 8.3 Hz, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.52–4.62 (m, 1H), 4.40–4.51 (m, 2H), 3.87 (s, 3H), 3.01–3.16 (m, 2H), 2.19–2.31 (m, 1H), 2.03–2.12 (m, 1H), 1.91–2.01 (m, 1H), 1.81 (dd, J = 14.1, 9.9 Hz, 1H), 1.54–1.72 (m, 3H), 0.93 (s, 9H); MS (ESI+) for C25H33ClN4O5m/z 505.1 (M + H)+; HRMS (ESI+) calcd for (M + H)+ 505.2212, found 505.2204. N-((1S)-1-{[((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-4-methoxy-1H-indole-2-carboxamide (36) Following the procedure described for the preparation 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 but substituting N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-4-methoxy-1H-indole-2-carboxamide and making noncritical variations provided a crude brown glass. This material was purified by Biotage MPLC (40 M column, 2–10% methanol/chloroform) to afford 415 mg (53%) of the title compound as a white solid. MS (ESI+) for C25H34N4O6m/z 487.2 (M + H)+. Alternatively, following the procedure described for the preparation of N-{(1S)-1-(cyclohexylmethyl)-2-[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-2-oxoethyl}-4-methoxy-1H-indole-2-carboxamide but substituting N-((1S)-1-{[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-4-methoxy-1H-indole-2-carboxamide and making noncritical variations provided a tan solid. This material was purified by Biotage MPLC (25 M column, 6–7% methanol/chloroform) to afford 100 mg (77%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.58 (s, 1H), 8.42 (d, J = 8 Hz, 1H), 8.37 (d, J = 8 Hz, 1H), 7.62 (s, 1H), 7.32 (s, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.04 (t, J = 8 Hz, 1H), 4.52 (m, 1H), 4.42 (m, 1H), 4.24 (dd, J = 8, 20 Hz, 1H), 4.12 (dd, J = 8, 20 Hz, 1H), 3.87 (s, 3H), 3.09 (m, 2H), 2.25 (m, 1H), 2.06 (m, 1H), 1.93 (m, 1H), 1.80 (dd, J = 8, 16 Hz, 1H), 0.93 (s, 9H); MS (ESI+) for C25H34N4O6m/z 487.2 (M + H)+; anal. calcd for C25H34N4O6·0.3 H2O: C, 61.03; H, 7.09; N, 11.39. Found: C, 61.07; H, 7.09; N, 11.22; HRMS (ESI+) calcd for C25H34N4O6 487.2551, found 487.2541. 4-Methoxy-N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide (37) Following the procedure described for the preparation of 4-methoxy-N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-1H-indole-2-carboxamide but substituting N-((1S)-1-{[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-4-methoxy-1H-indole-2-carboxamide and making noncritical variations provided a crude product. This material was purified by Biotage MPLC (40S column, 2–5% methanol/chloroform) to afford 21 mg (9%) of the title compound as a pale tan solid. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (s, 1H), 8.42 (d, J = 6.8 Hz, 1H), 7.62 (s, 1H), 7.32 (s, 1H), 7.08 (t, J = 7.7 Hz, 1H), 7.00 (d, J = 7.8 Hz, 1H), 6.49 (d, J = 7.3 Hz, 1H), 4.49–4.55 (m, 1H), 4.32–4.41 (m, 1H), 4.21–4.30 (m, 1H), 4.12 (t, J = 16.9 Hz, 1H), 3.87 (s, 3H), 3.23 (s, 3H), 3.01–3.16 (m, 2H), 2.20–2.32 (m, 1H), 2.03–2.15 (m, 1H), 1.87–1.98 (m, 1H), 1.73–1.85 (m, 1H), 1.54–1.70 (m, 3H), 0.93 (s, 9H); MS (ESI+) for C26H36N4O6m/z 501.2 (M + H)+; HRMS (ESI+) calcd for (M + H)+ 501.2708, found 501.2701. 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 (4) A solution of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide (488 mg, 0.99 mmol) and benzoylformic acid (195 mg, 1.3 mmol) in DMF (6.5 mL) was placed under an atmosphere of N2. This clear pale yellow solution was treated with cesium fluoride (350 mg, 2.3 mmol) followed by heating to 65 °C. After 4 h, the now yellow suspension was cooled to RT, diluted with ethyl acetate (60 mL), washed three times with water (30 mL) and once with brine (30 mL), dried over MgSO4, filtered, and concentrated to give (3S)-3-({N-[(4-methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl oxo(phenyl)acetate as a crude yellow foam. MS (ESI+) for C32H36N4O8m/z 605.2 (M + H)+. A solution of the crude (3S)-3-({N-[(4-methoxy-1H-indol-2-yl)carbonyl]-l-leucyl}amino)-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl oxo(phenyl)acetate in methanol (40 mL) was placed under an atmosphere of N2 and treated with potassium carbonate (7 mg, 0.05 mmol) with vigorous stirring. After 1 h, the volatiles were removed in vacuo (bath < 30 °C) to give a crude yellow glass. This material was purified by Biotage MPLC (25 M column, 6% methanol/chloroform) to afford 346 mg (73%) of the title compound as an off-white solid. 1H NMR (DMSO-d6) δ 11.56 (s, 1H), 8.44 (d, J = 8 Hz, 1H), 8.39 (d, J = 8 Hz, 1H), 7.61 (s, 1H), 7.35 (s, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.04 (t, J = 8 Hz, 1H), 4.46 (m, 2H), 4.25 (dd, J = 8, 20 Hz, 1H), 4.13 (dd, J = 8, 20 Hz, 1H), 3.87 (s, 3H), 3.10 (m, 2H), 2.28 (m, 1H), 2.08 (m, 1H), 1.92 (m, 1H), 1.70–1.53 (m, 5H), 0.93 (d, J = 8 Hz, 3H), 0.89 (d, J = 8 Hz, 3H); MS (ESI+) for C24H32N4O6m/z 473.2 (M + H)+. N1-((1S)-3-(Benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N2-(tert-butoxycarbonyl)-N2-methyl-l-leucinamide Following the procedure described for the preparation of tert-butyl [(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]carbamate but substituting Boc-N-methyl-Leu and making noncritical variations provided a crude brown oil. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound (123 mg, 47%) as a yellow gum. 1H NMR (400 MHz, CDCl3) δ 7.22–7.33 (m, 5H), 5.76 (bd, 1H), 4.73 (s, 1H), 4.46–4.59 (m, 2H), 4.08–4.27 (m, 2H), 3.14–3.28 (m, 2H), 2.68 (s, 3H), 2.16–2.38 (m, 2H), 1.88–2.00 (m, 1H), 1.56–1.86 (m, 5H), 1.41 (s, 9H), 0.94 (d, J = 8 Hz, 3H), 0.89 (d, J = 8 Hz, 3H). N-((1S)-1-{[((1S)-3-(Benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-N-methyl-1H-indole-2-carboxamide Following the procedure described for the preparation of N-[(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]-4-methoxy-1H-indole-2-carboxamide but substituting N1-((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N2-(tert-butoxycarbonyl)-N2-methyl-l-leucinamide and making noncritical variations provided a crude brown oil. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as a clear oil, 67 mg, 48%. 1H NMR (400 MHz, CDCl3) δ 9.83 (s, 1H), 7.95 (s, 1H), 7.26–7.36 (m, 5H), 7.18 (t, J = 8.0 Hz, 1H), 7.04 (d, J = 8.3 Hz, 1H), 7.00 (s, 1H), 6.48 (d, J = 7.8 Hz, 1H), 5.87 (s, 1H), 5.18–5.27 (m, 1H), 4.70 (s, 1H), 4.50–4.63 (m, 2H), 4.16–4.36 (m, 2H), 3.93 (s, 3H), 3.32 (s, 3H), 3.03–3.18 (m, 2H), 2.22 (s, 2H), 1.91–2.02 (m, 1H), 1.81 (t, J = 7.3 Hz, 3H), 1.66–1.72 (m, 1H), 1.55 (s, 1H), 0.87–1.01 (m, 6H); MS (API-ES−) for C32H40N4O6m/z 576.7 (M – H)−. N-((1S)-1-{[((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-N-methyl-1H-indole-2-carboxamide (38) Following the procedure described for the preparation of N-{(1S)-1-(cyclohexylmethyl)-2-[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-2-oxoethyl}-4-methoxy-1H-indole-2-carboxamide but substituting N-((1S)-1-{[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-N-methyl-1H-indole-2-carboxamide and making noncritical variations provided a crude clear glass. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as a white foam, 42 mg, 82%. 1H NMR (400 MHz, CDCl3) δ 10.16 (s, 1H), 8.26 (s, 1H), 7.18 (t, J = 8.0 Hz, 1H), 7.05 (d, J = 8.1 Hz, 1H), 6.99 (d, J = 2.3 Hz, 1H), 6.48 (d, J = 7.6 Hz, 1H), 6.09 (s, 1H), 5.14–5.27 (m, 1H), 4.51–4.65 (m, 1H), 4.25–4.50 (m, 2H), 3.94 (s, 3H), 3.26–3.46 (m, 3H), 3.11–3.24 (m, 1H), 3.01–3.11 (m, 1H), 1.48–2.39 (m, 9H), 0.88–1.02 (m, 6H); MS (API-ES–-) for C25H34N4O6m/z 485.3 (M – H)−. N2-(tert-Butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-norleucinamide Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting Boc-NorLeu-OH and making noncritical variations provided a golden syrup. This material was purified by LC (100 g 230–400 SiO2, 2.5–3.5% methanol/chloroform) to afford 727 mg (42%) of the title compound as a light yellow foam. 1H NMR (DMSO-d6) δ 8.45 (d, J = 8 Hz, 1H), 7.62 (s, 1H), 7.00 (d, J = 8 Hz, 1H), 4.59 (d, J = 16 Hz, 1H), 4.53 (d, J = 16 foam in a 42% isolated yield. 1H Hz, 1H), 4.38 (m, 1H), 3.80 (m, 1H), 3.15 (m, 1H), 3.06 (m, 1H), 2.22 (m, 1H), 2.07 (m, 1H), 1.98 (m, 1H), 1.63–1.51 (m, 4H), 1.36 (m, 9H), 1.24 (m, 4H), 0.83 (t, J = 8 Hz, 3H); MS (ESI+) for C19H32ClN3O5m/z 418.1 (M + H)+. N-((1S)-1-{[((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}pentyl)-4-methoxy-1H-indole-2-carboxamide Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-norleucinamide and making no other critical variations provided a crude yellow foam. This material was purified by Biotage MPLC (25 M column, 3% methanol/chloroform) to afford 254 mg (63%) of the title compound as an off-white solid. 1H NMR (DMSO-d6) δ 11.56 (s, 1H), 8.57 (d, J = 8 Hz, 1H), 8.39 (d, J = 4 Hz, 1H), 7.62 (s, 1H), 7.36 (s, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 4.58 (d, J = 16 Hz, 1H), 4.56 (d, J = 16 Hz, 1H), 4.43 (m, 1H), 4.35 (m, 1H), 3.87 (s, 3H), 3.09 (m, 2H), 2.27 (m, 1H), 2.08 (m, 1H), 1.97 (m, 1H), 1.74–1.54 (m, 4H), 1.30 (m, 4H), 0.86 (t, J = 8 Hz, 3H); MS (ESI+) for C24H31N4O5Cl m/z 491.1 (M + H)+; anal. calcd for C24H31ClN4O5: C, 58.71; H, 6.36; N, 11.41. Found: C, 58.66; H, 6.45; N, 11.22. N-((1S)-1-{[((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}pentyl)-4-methoxy-1H-indole-2-carboxamide (39) Following the procedure described for the preparation 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 but substituting of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}pentyl)-4-methoxy-1H-indole-2-carboxamide and making noncritical variations provided a crude yellow foam. This material was purified by Biotage MPLC (25 M column, 5–6% methanol/chloroform) to afford 82 mg (35%) of the title compound as a white foam. 1H NMR (DMSO-d6) δ 11.57 (s, 1H), 8.42 (d, J = 8 Hz, 1H), 8.38 (d, J = 8 Hz, 1H), 7.62 (s, 1H), 7.35 (s, 1H), 7.09 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.06 (t, J = 8 Hz, 1H), 4.44 (m, 2H), 4.25 (dd, J = 8, 20 Hz, 1H), 4.14 (dd, J = 8, 20 Hz, 1H), 3.87 (s, 3H), 3.08 (m, 2H), 2.28 (m, 1H), 2.10 (m, 1H), 1.91 (m, 1H), 1.74–1.54 (m, 4H), 1.32 (m, 4H), 0.87 (t, J = 8 Hz, 3H); MS (ESI+) for C24H32N4O6m/z 473.2 (M + H)+; anal. calcd for C24H32N4O6·0.6 H2O·0.2 ethyl acetate: C, 59.46; H, 7.01; N, 11.18. Found: C, 53.37; H, 6.94; N, 11.23; HRMS (ESI+) calcd for C24H32N4O6+H1 473.2395, found 473.2382. Methyl N-[(9H-Fluoren-9-ylmethoxy)carbonyl]-5-methyl-l-norleucinate To a solution of N-[(9H-fluoren-9-ylmethoxy)carbonyl]-5-methyl-l-norleucine (2.14 g, 5.8 mmol) in methanol (15 mL) is added toluene (30 mL) followed by the dropwise addition of TMS-diazomethane (2.9 mL, 2 M in hexane, 5.8 mmol). TLC analysis indicated incomplete reaction, and TMS-diazomethane was added dropwise until a yellow color persisted. At this time, the reaction was quenched by the addition of AcOH (1 mL) followed by concentration in vacuo. The residue was purified by Biotage flash chromatography, eluting with ethyl acetate/hexane to afford the title compound as a white solid, 2.18 g, 98%. 1H NMR (400 MHz, CDCl3) δ 7.76 (d, J = 7.6 Hz, 2H), 7.60 (dd, J = 7.2, 3.9 Hz, 2H), 7.40 (t, J = 7.2 Hz, 2H), 7.31 (t, J = 7.5 Hz, 2H), 5.26 (d, J = 8.6 Hz, 1H), 4.31–4.51 (m, 3H), 4.23 (t, J = 7.1 Hz, 1H), 3.75 (s, 3H), 1.78–1.93 (m, 1H), 1.60–1.76 (m, 1H), 1.45–1.60 (m, 1H), 1.05–1.34 (m, 2H), 0.88 (d, J = 4 Hz, 3H), 0.86 (d, J = 4 Hz, 3H); MS (APCI+) for C23H27NO4m/z 160.1 (M-Fmoc+H)+. Methyl N-(tert-Butoxycarbonyl)-5-methyl-l-norleucinate To a solution of methyl N-[(9H-fluoren-9-ylmethoxy)carbonyl]-5-methyl-l-norleucinate (2.18 g, 5.72 mmol) in DMF (50 mL) was added KF (2.33 g, 40.04 mmol) followed by triethylamine (1.70 mL, 12.24 mmol) and di-tert-butyl dicarbonate (7.39 mmol), and the mixture was stirred at an ambient temperature. After 4 h, TLC analysis indicated incomplete reaction and the reaction mixture was treated with a second portion of KF (2.7 g, 46.55 mmol) and BOC2O (800 mg, 3.67 mmol). After 16 h, the mixture was diluted with diethyl ether (300 mL), washed with satd. NaHCO3 (2 × 50 mL), 1 M hydrochloric acid (2 × 50 mL), NaHCO3 (50 mL), and brine (50 mL), dried over MgSO4, filtered, and the solvents were evaporated in vacuo to yield the crude product, which was purified by Biotage flash chromatography eluting with dichloromethane/hexane to afford the title compound as a clear oil, 980 mg, 66%. 1H NMR (400 MHz, CDCl3) δ 4.96 (d, J = 6.8 Hz, 1H), 4.21–4.32 (m, 1H), 3.72 (s, 3H), 1.72–1.85 (m, 1H), 1.46–1.66 (m, 2H), 1.43 (s, 9H), 1.11–1.29 (m, 2H), 0.88 (d, J = 4 Hz, 3H), 0.86 (d, J = 4 Hz, 3H); MS (API-ES+) for C13H25NO4m/z 282.2 (M + Na)+. N-(tert-Butoxycarbonyl)-5-methyl-l-norleucine To a solution of methyl N-(tert-butoxycarbonyl)-5-methyl-l-norleucinate (980 mg, 3.78 mmol) in THF (30 mL) at 0 °C was added a solution (precooled to 5 °C) of LiOH (1 M, 11.3 mL, 11.33 mmol), and the resulting mixture was stirred at 0 °C for 1 h and then allowed to warm to an ambient temperature. The reaction was acidified to pH 2 with 1 M hydrochloric acid and extracted with ethyl acetate (3 × 60 mL). The combined organics were washed with brine (100 mL), dried over MgSO4, filtered, and the solvent was removed in vacuo to yield the title compound as a clear oil, 990 mg, 99%. 1H NMR (400 MHz, CDCl3) δ 4.96 (d, J = 7.8 Hz, 1H), 4.23–4.34 (m, 1H), 1.75–1.93 (m, 2H), 1.60–1.72 (m, 1H), 1.50–1.59 (m, 1H), 1.44 (s, 9H), 1.19–1.30 (m, 1H), 0.88 (d, J = 4 Hz, 3H), 0.86 (d, J = 4 Hz, 3H); MS (API-ES+) for C12H23NO4m/z 268.1 (M + Na)+. N2-(tert-Butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-5-methyl-l-norleucinamide Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting N-(tert-butoxycarbonyl)-5-methyl-l-norleucine and making noncritical variations provided a crude golden oil. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as an off-white solid, 360 mg, 41%. 1H NMR (400 MHz, DMSO-d6) δ 8.45 (d, J = 8.1 Hz, 1H), 7.62 (s, 1H), 7.02 (d, J = 7.1 Hz, 1H), 4.49–4.62 (m, 2H), 4.33–4.44 (m, 1H), 3.78 (m, 1H), 3.15 (t, J = 8.7 Hz, 1H), 3.00–3.10 (m, 1H), 2.18–2.30 (m, 1H), 2.04–2.14 (m, 1H), 1.92–2.02 (m, 1H), 1.40–1.68 (m, 5H), 1.36 (s, 9H), 1.05–1.25 (m, J = 7.3 Hz, 2H), 0.83 (d, J = 1.52 Hz, 3H), 0.82 (d, J = 1.52 Hz, 3H); MS (API-ES+) for C20H34N3O5Cl m/z 454.2 (M + Na)+. N-((1S)-1-{[((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-4-methoxy-1H-indole-2-carboxamide Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-5-methyl-l-norleucinamide and making no other critical variations provided a crude yellow foam. This material was purified by Biotage MPLC (25 M column, 2.5–3.5% methanol/chloroform) to afford 307 mg (73%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.57 (s, 1H), 8.59 (d, J = 8 Hz, 1H), 8.41 (d, J = 4 Hz, 1H), 7.64 (s, 1H), 7.37 (s, 1H), 7.09 (t, J = 8 Hz, 1H), 7.00 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 4.59 (s, 2H), 4.44 (m, 1H), 4.35 (m, 1H), 3.87 (s, 3H), 3.08 (m, 2H), 2.26 (m, 1H), 2.07 (m, 1H), 1.98 (m, 1H), 1.70–1.51 (m, 5H), 1.25 (m, 2H), 0.88 (d, J = 4 Hz, 3H), 0.86 (d, J = 4 Hz, 3H); MS (ESI+) for C25H33ClN4O5m/z 505.2 (M + H)+; HRMS (ESI+) calcd for C25H33ClN4O5+H1 505.2212, found 505.2204. N-((1S)-1-{[((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-4-methoxy-1H-indole-2-carboxamide (40) Following the procedure described for the preparation 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 but substituting N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-4-methoxy-1H-indole-2-carboxamide and making noncritical variations provided a crude yellow foam. This material was purified by Biotage MPLC (25 M column, 5–5.5% methanol/chloroform) to afford 135 mg (50%) of the title compound as a white foam. 1H NMR (DMSO-d6) δ 11.57 (s, 1H), 8.42 (d, J = 8 Hz, 1H), 8.38 (d, J = 8 Hz, 1H), 7.62 (s, 1H), 7.35 (s, 1H), 7.09 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 5.06 (t, J = 8 Hz, 1H), 4.47–4.30 (m, 2H), 4.25 (dd, J = 8, 20 Hz, 1H), 4.14 (dd, J = 8, 20 Hz, 1H), 3.87 (s, 3H), 3.09 (m, 2H), 2.30 (m, 1H), 2.08 (m, 1H), 1.92 (m, 1H), 1.72–1.51 (m, 5H), 1.25 (m, 2H), 0.87 (d, J = 4 Hz, 3H), 0.86 (d, J = 4 Hz, 3H); MS (ESI+) for C25H34N4O6m/z 487.1 (M + H)+; HRMS (ESI+) calcd for C25H34N4O6 487.2551, found 487.2541. tert-Butyl [(1S)-2-[((1S)-3-(Benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]carbamate To a solution of tert-butyl ((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)carbamate (200 mg, 0.53 mmol) in dioxane (5 mL) was added 4 M hydrochloric acid/dioxane (5 mL), and the solution was stirred at an ambient temperature for 4 h before removing the solvents in vacuo, azeotroping the residue with toluene (2 × 10 mL), and drying in vacuo for 1 h. The crude hydrochloride salt was taken into DMF (3 mL), and the solution was cooled to 0 °C before adding N-Boc-cyclohexylalanine-OH (139 mg, 0.53 mmol), collidine (156 μL, 1.22 mmol), and HATU (194 mg, 0.53 mmol) in order, and the resulting suspension was stirred at 0 °C for 5 h. The reaction was quenched by the addition of water (30 mL), and the mixture was extracted with diethyl ether (3 × 75 mL). The combined organics were dried over MgSO4, filtered, and the solvents were removed in vacuo to yield the crude product, which was purified by flash chromatography, eluting with 1–3% methanol/dichloromethane to afford the title compound as a pale brown gum, 205 mg, 76%. The product was contaminated with ∼20% of another diastereoisomer. 1H NMR (400 MHz, CDCl3) δ 7.69 (d, J = 5.6 Hz, 1H), 7.26–7.42 (m, 5H), 5.93 (s, 1H), 4.94 (d, J = 7.6 Hz, 1H), 4.72 (m, 1H), 4.60 (d, J = 11.6 Hz, 1H), 4.55 (d, J = 11.6 Hz, 1H), 4.14–4.34 (m, 3H), 3.27 (m, 2H), 2.23–2.51 (m, 3H), 1.56–2.05 (m, 9H), 1.33–1.48 (m, 9H), 1.05–1.29 (m, 4H), 0.80–1.03 (m, 2H). N-[(1S)-2-[((1S)-3-(Benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]-4-methoxy-1H-indole-2-carboxamide To a solution of tert-butyl [(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]carbamate (200 mg, 0.38 mmol) in dioxane (4 mL) was added 4 M hydrochloric acid/dioxane (4 mL), and the solution was stirred at an ambient temperature for 2 h before removing the solvents in vacuo, azeotroping the residue with toluene (2 × 10 mL), and drying in vacuo for 1 h. The crude hydrochloride salt was taken into DMF (3 mL), and the solution was cooled to 0 °C before adding 4-methoxy-indole-2-carboxylic acid (73 mg, 0.38 mmol), collidine (125 μL, 0.95 mmol), and HATU (144 mg, 0.38 mmol) in order, and the resulting suspension was stirred at 0 °C for 6 h. The reaction was quenched by the addition of water (20 mL), and the mixture was extracted with diethyl ether (3 × 50 mL). The combined organics were washed with water (20 mL) and brine (20 mL), dried over MgSO4, filtered, and the solvents were removed in vacuo to yield the crude product, which was purified by Biotage flash chromatography, eluting with 1–3% methanol/dichloromethane to afford the title compound as a pale brown gum, 90 mg, 39%. The product was contaminated with ∼20% of another diastereomer from the previous step. 1H NMR (400 MHz, CDCl3) δ 9.59 (s, 1H), 8.13 (d, J = 6.6 Hz, 1H), 7.21–7.32 (m, 5H), 7.11 (t, J = 8.0 Hz, 1H), 7.02 (d, J = 1.5 Hz, 1H), 6.94 (d, J = 8.3 Hz, 1H), 6.72–6.78 (m, 1H), 6.42 (d, J = 7.8 Hz, 1H), 5.97 (s, 1H), 4.73 (m, 1H), 4.64 (m, 1H), 4.53 (d, J = 11.6 Hz, 1H), 4.46 (d, J = 11.6 Hz, 1H), 4.26 (d, J = 17.2 Hz, 1H), 4.15 (d, J = 17.4 Hz, 1H), 3.87 (s, 3H), 3.08–3.16 (m, 2H), 2.27–2.38 (m, 1H), 1.92 (m, 1H), 1.49–1.84 (m, 9H), 1.26–1.42 (m, 1H), 0.98–1.23 (m, 4H), 0.78–0.98 (m, 2H); MS (APCI+) for C34H42N4O6m/z 603.2 (M + H)+. N-{(1S)-1-(Cyclohexylmethyl)-2-[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-2-oxoethyl}-4-methoxy-1H-indole-2-carboxamide (41) To a solution of N-[(1S)-2-[((1S)-3-(benzyloxy)-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]-1-(cyclohexylmethyl)-2-oxoethyl]-4-methoxy-1H-indole-2-carboxamide (80 mg, 0.13 mmol) in EtOH (3 mL) was added 10% Pd/C (50 mg), and the suspension was hydrogenated at an ambient temperature under H2 (1 atm balloon) for 5 h. The catalyst was removed by filtration, and the solvents were evaporated in vacuo to yield the crude product, which was purified by Biotage flash chromatography, eluting with 2–10% methanol/dichloromethane to afford the title compound, 37 mg, 55% as a white solid. 1H NMR (400 MHz, MeOD) δ 7.19 (s, 1H), 7.05 (t, J = 8.0 Hz, 1H), 6.93 (d, J = 8.1 Hz, 1H), 6.41 (d, J = 7.8 Hz, 1H), 4.52–4.59 (m, 2H), 4.27 (m, 2H), 3.83 (s, 3H), 3.08–3.21 (m, 2H), 2.47 (m, 1H), 2.13–2.24 (m, 1H), 1.92–2.03 (m, 1H), 1.53–1.79 (m, 9H), 1.31–1.45 (m, 1H), 1.04–1.29 (m, 3H), 0.81–1.02 (m, 2H); MS (APCI+) for C27H36N4O6m/z 513.2. (M + H)+; anal. calcd for C27H36N4O6· 0.8 H2O: C, 61.53; H, 7.19; N, 10.63. Found: C, 61.83; H, 7.12; N, 10.27. N-(tert-Butoxycarbonyl)-N-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-phenylalaninamide Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting Boc-Phe-OH and making noncritical variations provided a crude brown oil. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as a white solid, 351 mg, 36%. 1H NMR (400 MHz, CDCl3) δ 8.02 (s, 1H), 7.19–7.31 (m, 5H), 5.77 (s, 1H), 5.10 (d, J = 6.1 Hz, 1H), 4.52–4.57 (m, 1H), 4.44 (m, 1H), 4.01–4.12 (m, 2H), 3.26–3.37 (m, 2H), 3.01–3.08 (m, 2H), 2.29–2.37 (m, 1H), 2.15–2.25 (m, 1H), 1.98–2.06 (m, 1H), 1.75–1.91 (m, 2H), 1.40 (s, 9H); MS (API-ES−) for C22H30N3O5Cl m/z 450.2 (M – H)−. N-((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N-[(4-methoxy-1H-indol-2-yl)carbonyl]-l-phenylalaninamide Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting N-(tert-butoxycarbonyl)-N-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-phenylalaninamide and making noncritical variations provided a crude green solid. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as a white solid, 300 mg, 91%. 1H NMR (400 MHz, DMSO-d6) δ 11.52 (d, J = 2.0 Hz, 1H), 8.68 (d, J = 7.8 Hz, 1H), 8.61 (d, J = 7.8 Hz, 1H), 7.61 (s, 1H), 7.37 (d, J = 7.1 Hz, 2H), 7.31 (d, J = 1.8 Hz, 1H), 7.26 (t, J = 7.6 Hz, 2H), 7.16 (t, J = 7.2 Hz, 1H), 7.07 (t, 1H), 6.97 (d, J = 8.1 Hz, 1H), 6.49 (d, J = 7.6 Hz, 1H), 4.68 (m, 1H), 4.38–4.49 (m, 3H), 3.88 (s, 3H), 2.97–3.17 (m, 4H), 2.20–2.32 (m, 1H), 2.02–2.14 (m, 1H), 1.93–2.02 (m, 1H), 1.52–1.69 (m, 2H); MS (APCI±) for C27H29N4O5Cl m/z 526.0 (M + H)−. N-((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N-[(4-methoxy-1H-indol-2-yl)carbonyl]-l-phenylalaninamide (42) Following the procedure described for the preparation 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 but substituting N-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-N-[(4-methoxy-1H-indol-2-yl)carbonyl]-l-phenylalaninamide and making noncritical variations provided a crude greenish gum. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as an off-white solid, 123 mg, 44%. 1H NMR (400 MHz, DMSO-d6) δ 11.50 (d, J = 2.0 Hz, 1H), 8.58 (dd, J = 8.2, 3.9 Hz, 2H), 7.63 (s, 1H), 7.35–7.43 (m, 2H), 7.31 (d, J = 1.8 Hz, 1H), 7.27 (t, J = 7.6 Hz, 2H), 7.17 (t, J = 7.3 Hz, 1H), 7.08 (t, J = 8.0 Hz, 1H), 6.98 (d, J = 8.1 Hz, 1H), 6.48 (d, J = 7.8 Hz, 1H), 5.06 (t, J = 6.1 Hz, 1H), 4.72 (m, 1H), 4.48 (m, 1H), 4.16 (m, 2H), 3.89 (s, 3H), 2.97–3.18 (m, 4H), 2.24–2.36 (m, 1H), 2.04–2.18 (m, 1H), 1.88–2.01 (m, 1H), 1.55–1.76 (m, 2H); MS (APCI+) for C27H30N4O6m/z 507.1 (M + H)+; anal. calcd for C27H30N4O6· 1.25 H2O: C, 61.29; H, 6.19; N, 10.59. Found: C, 61.37; H, 6.06; N, 10.49. N-((1S)-1-{[((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-l-leucinamide and indole-2-carboxylic acid and making no other critical variations provided a crude yellow foam. This material was purified by Biotage MPLC (40 M column, 2.5–3.5% methanol/chloroform) to afford 1.06 g (62%) of the title compound as a light yellow foam. 1H NMR (DMSO-d6) δ 11.59 (s, 1H), 8.58 (d, J = 8 Hz, 1H), 8.50 (d, J = 8 Hz, 1H), 7.64 (s, 1H), 7.61 (d, J = 8 Hz, 1H), 7.41 (d, J = 8 Hz, 1H), 7.23 (s, 1H), 7.17 (t, J = 8 Hz, 1H), 7.02 (t, J = 8 Hz, 1H), 4.62–4.50 (m, 3H), 4.45 (m, 1H), 3.10 (m, 2H), 2.25 (m, 1H), 2.08 (m, 1H), 1.96 (m, 1H), 1.80 (m, 1H), 1.72–1.58 (m, 3H), 0.94 (s, 9H); MS (ESI+) for C24H31ClN4O4m/z 475.1 (M + H)+; anal. calcd for C24H31ClN4O4·0.35 CHCl3: C, 56.59; H, 6.12; N, 10.84. Found: C, 56.38; H, 6.18; N, 10.75; HRMS (ESI+) calcd for C24H31ClN4O4 475.2107, found 475.2122. N-((1S)-1-{[((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide (43) Following the procedure described for the preparation 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 but substituting N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide and making noncritical variations provided a crude yellow foam. This material was purified by Biotage MPLC (40 M column, 4.5–5.5% methanol/chloroform) to afford 730 mg (72%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.59 (s, 1H), 8.49 (d, J = 8 Hz, 1H), 8.43 (d, J = 8 Hz, 1H), 7.62 (s, 1H), 7.60 (s, 1H), 7.41 (d, J = 8 Hz, 1H), 7.23 (s, 1H), 7.17 (t, J = 8 Hz, 1H), 7.02 (t, J = 8 Hz, 1H), 5.05 (t, J = 8 Hz, 1H), 4.56 (m, 1H), 4.43 (m, 1H), 4.25 (dd, J = 8, 20 Hz, 1H), 4.13 (dd, J = 8, 20 Hz, 1H), 3.10 (m, 2H), 2.25 (m, 1H), 2.07 (m, 1H), 1.93 (m, 1H), 1.80 (m, 1H), 1.64 (m, 3H), 0.94 (s, 9H); MS (ESI+) for C24H32N4O5m/z 457.1 (M + H)+; anal. calcd for C24H32N4O5·0.2 CHCl3·0.2 ethyl acetate·0.25 H2O: C, 59.75; H, 6.88; N, 11.15. Found: C, 59.67; H, 6.72; N, 11.03; HRMS (ESI+) calcd for C24H32N4O5 457.2446, found 457.2439. N-((1S)-1-{[((1S)-3-Methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide (44) Following the procedure described for the preparation of 4-methoxy-N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-1H-indole-2-carboxamide but substituting N-((1S)-1-{[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide and making noncritical variations provided a crude tan foam. This material was purified by Biotage MPLC (25 M column, 3.5–4.5% methanol/chloroform) to afford 43 mg (15%) of the title compound as a white solid. 1H NMR (DMSO-d6) δ 11.58 (s, 1H), 8.48 (apar t, J = 8 Hz, 2H), 7.61 (apar d, J = 8 Hz, 2H), 7.41 (d, J = 8 Hz, 1H), 7.23 (s, 1H), 7.17 (t, J = 8 Hz, 1H), 7.02 (t, J = 8 Hz, 1H), 4.55 (m, 1H), 4.37 (m, 1H), 4.25 (d, J = 20 Hz, 1H), 4.10 (d, J = 20 Hz, 1H), 3.23 (s, 3H), 3.06 (m, 2H), 2.27 (m, 1H), 2.07 (m, 1H), 1.91 (m, 1H), 1.79 (m, 1H), 1.69 (m, 3H), 0.94 (s, 9H); MS (ESI+) for C25H34N4O5m/z 471.2 (M + H)+; anal. calcd for C25H34N4O5·0.2 ethyl acetate·0.75 H2O: C, 61.76; H, 7.46; N, 11.17. Found: C, 61.85; H, 7.15; N, 11.02; HRMS (ESI+) calcd for C25H34N4O5 471.2602, found 471.2595. N-((1S)-1-{[((1S)-3-Ethoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide (45) Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3,3-dimethylbutyl)-1H-indole-2-carboxamide but substituting iodoethane and making noncritical variations provided a crude tan foam. This material was purified by Biotage MPLC (25 M column, 3–5% methanol/chloroform) to afford 19 mg (6%) of the title compound as an off-white solid. 1H NMR (DMSO-d6) δ 11.58 (s, 1H), 8.48 (d, J = 8 Hz, 1H), 8.45 (d, J = 8 Hz, 1H), 7.61 (apar d, J = 8 Hz, 2H), 7.41 (d, J = 8 Hz, 1H), 7.23 (s, 1H), 7.17 (t, J = 8 Hz, 1H), 7.02 (t, J = 8 Hz, 1H), 4.56 (m, 1H), 4.40 (m, 1H), 4.28 (d, J = 16 Hz, 1H), 4.13 (d, J = 16 Hz, 1H), 3.41 (m, 2H), 3.06 (m, 2H), 2.26 (m, 1H), 2.09 (m, 1H), 1.91 (m, 1H), 1.82 (m, 1H), 1.63 (m, 3H), 1.08 (t, J = 8 Hz, 3H), 0.94 (s, 9H); MS (ESI+) for C26H36N4O5m/z 485.2 (M + H)+; HRMS (ESI+) calcd for C26H36N4O5 485.2759, found 485.2756. N1-((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-N2-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucinamide Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-l-leucinamide and (2R)-tetrahydrofuran-2-carboxylic acid and making noncritical variations provided a crude product. This crude material was purified by Biotage MPLC (40 M cartridge, chloroform mobile phase with 2% methanol followed by 3% methanol, sample loaded in chloroform) resulting in the isolation of 1.13 g (61%) of the title compound as a light yellow foam. Rf = 0.27 (95:5 dichloromethane/methanol); 1H NMR (400 MHz, DMSO-d6) δ 8.47 (d, J = 8 Hz, 1H), 7.72 (d, J = 8 Hz, 1H), 7.68 (s, 1H), 4.55 (s, 2H), 4.44–4.36 (m, 1H), 4.35–4.27 (m, 1H), 4.21 (dd, J = 8, 5 Hz, 1H), 3.95–3.86 (m, 1H), 3.79–3.71 (m, 1H), 3.18–3.07 (m, 2H), 2.21 (td, J = 9, 4 Hz, 1H), 2.13–2.03 (m, 2H), 1.97–1.88 (m, 1H), 1.85–1.74 (m, 3H), 1.68–1.56 (m, 4H), 0.88 (s, 9H); MS (ESI+) for C20H32ClN3O5m/z 430 (M + H). N1-((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-N2-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucinamide (46) Following the procedure described for the preparation 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 but substituting N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-N2-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucinamide and making noncritical variations provided a crude product. This material was purified by a series of two radial chromatographies (first −2 mm plate, 90:10 dichloromethane/methanol to 90:20, sample loaded in 90:10) (second −1 mm plates, 90:10 dichloromethane/methanol to 95:5, sample loaded in dichloromethane) to provide 0.402 g (46%) of the title compound as a light yellow foam. Rf = 0.44 (90:10 dichloromethane/methanol); 1H NMR (400 MHz, DMSO-d6) δ 8.27 (d, J = 8 Hz, 1H), 7.71 (d, J = 9 Hz, 1H), 7.65 (s, 1H), 5.11 (t, J = 6 Hz, 1H), 4.46–4.38 (m, 1H), 4.37–4.30 (m, 1H), 4.24–4.15 (m, 2H), 4.14–4.08 (m, 1H), 3.96–3.87 (m, 1H), 3.79–3.70 (m, 1H), 3.18–3.06 (m, 2H), 2.25–2.16 (m, 1H), 2.13–2.02 (m, 2H), 1.87–1.75 (m, 4H), 1.66–1.54 (m, 4H), 0.88 (s, 9H); MS (ESI+) for C20H33N3O6m/z 412 (M + H). Anal. calcd for C20H33N3O6·0.5H2O: C, 57.12; H, 8.16; N, 9.99. Found: C, 57.25; H, 7.93; N, 9.68. HRMS (ESI+) calcd for C20H33N3O6+H 412.2442, found 412.2447. N1-((1S)-3-Methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-N2-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucinamide (47) Following the procedure described for the preparation of 4-methoxy-N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-1H-indole-2-carboxamide but substituting N1-((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-4-methyl-N2-[(2R)-tetrahydrofuran-2-ylcarbonyl]-l-leucinamide and making noncritical variations provided a crude product. This material was purified by radial chromatography (1 mm plate, 95:5 dichloromethane/methanol, sample loaded in dichloromethane) resulting in the isolation of 45.6 mg (22%) of the title compound as a light orange gum and as a mixture of diastereomers. Rf = 0.30 (95:5 dichloromethane/methanol); 1H NMR (400 MHz, DMSO-d6, major diastereomer) δ 8.33 (d, J = 8 Hz, 1H), 7.70 (d, J = 9 Hz, 1H), 7.66 (s, 1H), 4.39–4.28 (m, 2H), 4.24–4.07 (m, 3H), 3.94–3.86 (m, 1H), 3.75 (q, J = 7 Hz, 1H), 3.24 (s, 3H), 3.18–3.06 (m, 2H), 2.27–2.15 (m, 1H), 2.14–2.03 (m, 2H), 1.92–1.73 (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) oxide (182 mg, 0.79 mmol) in dichloromethane (12 mL) was placed under an atmosphere of N2. The resulting black thick suspension was heated to reflux for 18 h, treated with a second portion of iodomethane (0.12 mL, 2.0 mmol), and returned to reflux for an additional 24 h. The reaction was cooled to RT, diluted with dichloromethane (20 mL), washed once with water (20 mL), once with brine (20 mL), dried over MgSO4, filtered, and concentrated to give a crude tan solid. This material was purified by Biotage MPLC (25 M column, 3.5–4.5% methanol/chloroform) to afford 19 mg (10%) of the title compound as an off-white solid. 1H NMR (DMSO-d6) δ 11.57 (s, 1H), 8.48 (d, J = 8 Hz, 1H), 8.40 (d, J = 8 Hz, 1H), 7.63 (s, 1H), 7.35 (s, 1H), 7.08 (t, J = 8 Hz, 1H), 6.99 (d, J = 8 Hz, 1H), 6.49 (d, J = 8 Hz, 1H), 4.47 (m, 1H), 4.38 (m, 1H), 4.25 (d, J = 16 Hz, 1H), 4.11 (d, J = 16 Hz, 1H), 3.87 (s, 3H), 3.23 (s, 3H), 3.08 (m, 2H), 2.31 (m, 1H), 2.08 (m, 1H), 1.92 (m, 1H), 1.72–1.51 (m, 5H), 0.93 (d, J = 8 Hz, 3H), 0.88 (d, J = 8 Hz, 3H); MS (ESI+) for C25H34N4O6m/z 487.2 (M + H)+; HRMS (ESI+) calcd for C25H34N4O6+H1 487.2551, found 487.2563. N-((1S)-1-{[((1S)-3-Chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-1H-indole-2-carboxamide Following the procedure described for the preparation of N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-4-methoxy-1H-indole-2-carboxamide but substituting indole-2-carboxylic acid and making noncritical variations provided a crude orange foam. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as an off-white solid, 1.75 g, 82%. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (s, 1H), 8.64 (d, J = 7.8 Hz, 1H), 8.50 (d, J = 7.8 Hz, 1H), 7.55–7.69 (m, 2H), 7.42 (d, J = 8.3 Hz, 1H), 7.26 (d, J = 1.5 Hz, 1H), 7.16 (m, 1H), 7.02 (t, J = 7.5 Hz, 1H), 4.53–4.66 (m, 2H), 4.39–4.52 (m, 2H), 2.94–3.18 (m, 2H), 2.22–2.35 (m, 1H), 2.03–2.16 (m, 1H), 1.89–2.02 (m, 1H), 1.45–1.82 (m, 5H), 0.93 (d, J = 6.3 Hz, 3H), 0.88 (d, J = 6.3 Hz, 3H); MS (APCI−) for C23H29N4O4Cl m/z 459.1 (M – H)−. N-((1S)-1-{[((1S)-3-Hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-1H-indole-2-carboxamide (49) Following the procedure described for the preparation 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 but substituting N-((1S)-1-{[((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-1H-indole-2-carboxamide and making noncritical variations provided a crude black gum. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as an off-white solid, 218 mg, 18%. 1H NMR (400 MHz, DMSO-d6) δ 11.58 (s, 1H), 8.42–8.61 (m, 2H), 7.61 (d, J = 8.6 Hz, 2H), 7.41 (d, J = 8.1 Hz, 1H), 7.26 (s, 1H), 7.17 (t, J = 7.6 Hz, 1H), 7.02 (t, J = 7.5 Hz, 1H), 5.02 (t, 1H), 4.38–4.58 (m, 2H), 4.09–4.32 (m, 2H), 3.01–3.17 (m, 2H), 2.24–2.38 (m, 1H), 2.03–2.22 (m, 2H), 1.92 (m, 1H), 1.46–1.77 (m, 4H), 0.85–0.99 (m, 6H); MS (APCI+) for C23H30N4O5m/z 443.1 (M + H)+; anal. calcd for C23H30N4O5·0.55 H2O·0.05 DCM: C, 60.62; H, 6.89; N, 12.27. Found: C, 60.83; H, 6.90; N,11.93. N-((1S)-1-{[((1S)-3-Methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-1H-indole-2-carboxamide (50) Following the procedure described for the preparation of 4-methoxy-N-((1S)-1-{[((1S)-3-methoxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-4-methylpentyl)-1H-indole-2-carboxamide but substituting N-((1S)-1-{[((1S)-3-hydroxy-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)amino]carbonyl}-3-methylbutyl)-1H-indole-2-carboxamide and making noncritical variations provided a crude pale brown oil. This material was purified by Biotage flash chromatography, eluting with methanol/dichloromethane to afford the title compound as a white foam, 15 mg, 7%. 1H NMR (CDCl3) δ 9.52 (s, 1H), 8.38 (d, J = 6.1 Hz, 1H), 7.62 (d, J = 8.1 Hz, 1H), 7.40 (dd, J = 8.1, 3.8 Hz, 1H), 7.20–7.29 (m, 1H), 7.11 (t, J = 7.5 Hz, 1H), 6.98 (dd, J = 11.4, 1.5 Hz, 1H), 6.87 (d, J = 8.3 Hz, 1H), 5.98 (d, J = 13.1 Hz, 1H), 4.71–4.88 (m, 1H), 4.63 (m, 1H), 4.08–4.33 (m, 2H), 3.38–3.44 (s, 3H), 3.08–3.33 (m, 2H), 2.28–2.63 (m, 2H), 2.13–2.25 (m, 1H), 1.55–2.10 (m, 4H), 0.85–1.03 (m, 6H); MS (APCI−) for C24H32N4O5m/z 455.2 (M – H)−. SARS CoV-1 Protease FRET Assay and Analysis Proteolytic activity of coronavirus 3CL protease is measured using a continuous fluorescence resonance energy-transfer assay. The SARS 3CLpro FRET assay measures the protease-catalyzed cleavage of TAMRA-SITSAVLQSGFRKMK-(DABCYL)-OH to TAMRA-SITSAVLQ and SGFRKMK(DABCYL)-OH. The fluorescence of the cleaved TAMRA (ex. 558 nm/em. 581 nm) peptide was measured using a TECAN SAFIRE fluorescence plate reader over the course of 10 min. Typical reaction solutions contained 20 mM HEPES (pH 7.0), 1 mM EDTA, 4.0 FRET substrate, 4% DMSO, and 0.005% Tween-20. Assays were initiated with the addition of 25 nM SARS CoV-1 3CLpro nucleotide sequence 9985–10902 of the Urbani strain of SARS coronavirus complete genome sequence (NCBI accession number AY278741). Percent inhibition was determined in duplicate at a 0.001 mM level of inhibitor. Data was analyzed with the nonlinear regression analysis program KaleidaGraph using the equationwhere offset equals the fluorescence signal of the uncleaved peptide substrate, and limit equals the fluorescence of the fully cleaved peptide substrate. The kobs is the first-order rate constant for this reaction and, in the absence of any inhibitor, represents the utilization of a substrate. In an enzyme start reaction, which contains an irreversible inhibitor, and where the calculated limit is less than 20% of the theoretical maximum limit, the calculated kobs represents the rate of inactivation of coronavirus 3CL protease. The slope (kobs/I) of a plot of kobs vs [I] is a measure of the avidity of the inhibitor for an enzyme. For very fast irreversible inhibitors, kobs/I is calculated from observations at only one or two [I] rather than as a slope. For the determination of IC50 values for reversible inhibitors, the data was analyzed with the nonlinear regression analysis programs Xlfit3.05 (IDBS, Guildford, U.K.) or GraphPad Prism 8.02 (GraphPad Software San Diego, CA). SARS CoV-2 Protease FRET Assay and Analysis The proteolytic activity of the main protease, 3CLpro, of SARS CoV-2 was monitored using a continuous fluorescence resonance energy-transfer (FRET) assay. The SARS CoV-2 3CLpro assay measures the activity of full-length SARS CoV-2 3CL protease to cleave a synthetic fluorogenic substrate peptide with the following sequence DABCYL-KTSAVLQ-SGFRKME-EDANS modeled on a consensus peptide.50 The fluorescence of the cleaved EDANS peptide (excitation 340 nm/emission 490 nm) is measured using a fluorescence intensity protocol on a Flexstation reader (Molecular Devices). The fluorescent signal is reduced in the presence of PF-00835231, a potent inhibitor of SARS CoV-2 3CLpro. The assay reaction buffer contained 20 mM Tris–HCl (pH 7.3), 100 nM NaCl, 1 mM EDTA, 5 mM TCEP, and 25 μM peptide substrate. Enzyme reactions were initiated with the addition of 15 nM SARS CoV-2 3CL protease and allowed to proceed for 60 min at 23 °C. Percent inhibition or activity was calculated based on control wells containing no compound (0% inhibition/100% activity) and a control compound (100% inhibition/0% activity). IC50 values were generated using a four-parameter fit model using ABASE software (IDBS). Ki values were fit to the Morrison equation with the enzyme concentration parameter fixed to 15 nM, the Km parameter fixed to 14 μM, and the substrate concentration parameter fixed to 25 μM using Activity Base software (IDBS). SARS CoV-1 Antiviral Assays All assays were performed in BSL3 containment. Vero 76 cells were plated at 10 000 cells per well using phenol red-free DMEM or IMEM (Gibco). After adhering for 2 h at 37 °C, various concentrations of compound (320, 100, 33, 10, 3.3, 1.0, 0.3, or 0.1 μM) were added and the cells were infected with 2.6 × 103 PFU/well SARS CoV Toronto-2 (provided as a gift from Dr. Heinz Feldman (NIAID, Hamilton, MT)) or mock-infected with the medium only. After 66 h, cell viability was determined using either the neutral red method or the CellTiter-Glo Luminescent Cell Viability Assay (Promega, Madison, WI). For the neutral red method, the cells were washed twice with PBS, and 100 μL of DMEM pH 4.5 containing 0.066% neutral red was added to the cells for 2 h at 37 °C. The cells were again washed twice with PBS, 100 μL of buffer solution (50% EtOH, 1% acetic acid) was added, and the OD was read at 540 nM after a 10 min incubation at 37 °C with shaking. Data are expressed as the percent of neutral red or luminescent signal in wells of compound-treated cells compared to the signal in wells of uninfected, compound-free cells. The 50% effective concentration (EC50) is calculated as the concentration of the compound that increases the percent of the neutral red or luminescent signal in infected, compound-treated cells to 50% of that produced by uninfected, compound-free cells. The 50% cytotoxicity concentration (CC50) is calculated as the concentration of the compound that decreases the percent of the neutral red or luminescent signal in uninfected, compound-treated cells to 50% of that produced in uninfected, compound-free cells.51,52 hCOV 229E Antiviral assays MRC-5 cells were plated at 10 000 cells per well using phenol red-free MEM (Gibco). Various concentrations of compound (320, 100, 33, 10, 3.3, 1.0, 0.3, or 0.1 μM) were added, and the cells were infected with an amount of hCoV 229E, which caused 80% cell death in 4 days or mock-infected with the medium only. After 4 days, cell viability was determined using the XTT dye reduction method.53 Data are expressed as the percent of neutral red or luminescent signal in wells of compound-treated cells compared to the signal in wells of uninfected, compound-free cells. The 50% effective concentration (EC50) is calculated as the concentration of the compound that increases the percent of the neutral red or luminescent signal in infected, compound-treated cells to 50% of that produced by uninfected, compound-free cells. The 50% cytotoxicity concentration (CC50) is calculated as the concentration of the compound that decreases the percent of the neutral red or luminescent signal in uninfected, compound-treated cells to 50% of that produced in uninfected, compound-free cells. Other Antiviral Assays The following antiviral assays for HCMV,54 HIV-RF,55 HRV-14, and HRV-16,54 as well as the HCV replicon,56,57 were performed as described in the above references. Expression and Purification of CoV-2 3CL Protease The expression and purification strategy followed previous studies on SARS CoV-1 3CLpro.58 Genes encoding SARS CoV-1 3CLpro and SARS CoV-2 Mpro MN908947.3 were synthesized with codon usage optimized for Escherichia coli expression (Genscript and IDT). Genes were cloned into a modified pET24a vector to produce a TEV-cleavable N-terminal 6xHis tag under the T7 promoter control. BL21(DE3) cells (LifeTech) were grown in Terrific Broth (Teknova) at 37 °C until an OD600 = 0.6–0.8 and induced with 0.4 M IPTG for 5 h at 30 °C. Cell pellets were stored at −80 °C until purification. Cell pellets were resuspended and lysed by microfluidization in Buffer A (20 mM Tris pH 8.0 + 150 mM NaCl). Lysates were clarified at 25,000 × g for 1 h at 4 °C. The soluble lysate was loaded onto a nickel affinity column (Probond) and washed sequentially with Buffer A + 5 mM and 20 mM imidazole. The proteases were eluted with Buffer A + 300 mM imidazole. The His-tag was removed by TEV protease (1:40) during an overnight dialysis step in Buffer A + 1 mM DTT. The CoV Mpro proteins were further purified on a HiTrap Q hp (GE Healthcare), and the Q-flow-through material was concentrated and loaded onto a 26/60 Superdex-75 (GE Healthcare) gel filtration column equilibrated with Buffer B (20 mM Tris pH 7.8 + 150 mM NaCl + 1 mM EDTA + 1 mM DTT). Final proteins were concentrated from 5 to 25 mg/mL and were directly moved to crystallization experiments or snap-frozen in liquid nitrogen for storage. Crystallization/Soak Protocols for SARS1 with 2 Crystals of compound 2 bound to SARS1/CoV-1 DC2 protease were produced via cocrystallization. SARS1/CoV-1 DC2 protease at 10.00 mg/mL was incubated with a 3-fold molar excess of compound 2 for 18 h at 4 °C. The complex was then passed through a 0.45 μM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 μL of 4% w/v PEG 6000, 0.1 M MES pH 6.0, and 2.5 mM DTT were dispensed, and then sitting drops consisting of 0.3 μL protein were set up against a 0.3 μL well buffer. Crystallization plates were incubated at 21 °C, and rectangular crystals measuring 0.1 × 0.25 × 0.25 mm3 grew within 24 h. Cocrystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol. Crystallization/Soak Protocols for SARS1 with 28 Crystals of compound 28 bound to SARS1/CoV-1 DC2 protease were produced via cocrystallization. SARS1/CoV-1 DC2 protease at 10.00 mg/mL was incubated with a 3-fold molar excess of compound 28 for 18 h at 4 °C. The complex was then passed through a 0.45 μM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 μL of 10% w/v PEG 8000, 0.2 M sodium chloride, 0.1 M sodium potassium phosphate pH 6.2, and 10 mM TCEP were dispensed, and then sitting drops consisting of 0.3 μL protein were set up against a 0.3 μL well buffer. Crystallization plates were incubated at 21 °C, and rectangular crystals measuring 0.1 × 0.25 × 0.25 mm3 grew within 24 h. Cocrystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol. Crystallization/Soak Protocols for SARS1 and SARS2 with 4 (PF-00835231) LJEC2520 + PF-00835231 Crystals of PF-00835231 bound to SARS1/CoV-1 DC2 protease via cocrystallization: Freshly prepared SARS1/CoV-1 DC2 protease at 10.00 mg/mL was incubated with a 3-fold molar excess of PF-00835231 for 18 h at 4 °C. The complex was then passed through a 0.45 μM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 μL of 10% w/v PEG 6000, 0.1 M MES pH 6.0, and 10% glycerol were dispensed, and then sitting drops consisting of 0.15 μL protein were set up against a 0.15 μL well buffer. Crystallization plates were incubated at 21 °C, and rectangular crystals measuring 0.2 × 0.25 × 0.15 mm3 grew overnight. Crystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol. LJEC2521 + PF-00835231 Crystals of PF-00835231 bound to SARS2/CoV-2 mature protease via cocrystallization: Freshly prepared SARS2/CoV-2 mature protease at 11.3 mg/mL was incubated with a 3-fold molar excess of PF-00835231 for 18 h at 4 °C. The complex was then passed through a 0.45 μM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 μL of 15% v/v 2-propanol, 0.1 M citric acid pH 5.0, and 10% w/v PEG 10 000 were dispensed, and then sitting drops consisting of 0.3 μL protein and a 0.3 μL well buffer were set up. Crystallization plates were incubated at 13 °C, and crystals shaped as rectangular blocks measuring 0.1 × 0.2 × 0.2 mm3 grew overnight. Crystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol. LJEC2522 + PF-00835231 Crystals of PF-00835231 bound to SARS2/CoV-2 DC2 protease via soaking: Freshly prepared SARS2/CoV-2 DC2 protease at 25.8 mg/mL was passed through a 0.45 mM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 mL of 0.2 M potassium sodium tartrate tetrahydrate and 20% w/v PEG 3350 were dispensed, and then sitting drops consisting of 0.3 μL protein were set up in a 1:1 ratio with a well buffer. Crystallization plates were incubated at 13 °C, and large crystals shaped as beveled plates measuring 0.35 × 0.2 × 0.025 mm3 grew after 48 h. PF-00835231 (in 100% DMSO solution) was introduced to the drop (in situ), at a final concentration of 1 mM, and then incubated at 13 °C for 24 h. Soaked crystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol. Structure determination. X-ray diffraction data were collected at the IMCA-CAT 17-ID beamline of Advanced Photon Source at Argonne National Labs and processed using autoPROC. Structure of the SARS CoV main protease in complex with PF-835231 was determined by molecular replacement using the published protein structure (PDBID 1Q2W) as the starting model in program Phaser and refined iteratively using autoBUSTER followed by model building in Coot. Structure of the SARS CoV-2 main protease in complex with PF-835231 was determined similarly by rigid body refinement using the SARS CoV main protease structure in complex with the same ligand as the starting model.