Reaction Steps
Methyl 1-{[4-(benzyloxy)amino]methyl)}-1-phenylsulfonyl-1H-pyrrolo[2,3-c]pyridine-5-carboxylate. To a stirred solution of methyl 4-bromomethyl-1-phenylsulfonyl-1H-pyrrolo[2,3-c]pyridine-5-carboxylate (0.30 g, 0.73 mmol) [prepared acc. X. Doisy et al., Bioorg. Med. Chem. 1999, 7, 921-932]in DMF (20 mL) were added benzyloxyamine (0.45 g, 3.65 mmol) and triethylamine (0.51 mL, 3.65 mmol). The resulting mixture was stirred for 16 hours at ambient temperature. It was quenched with water (30 mL), and extracted with ethyl acetate (3×30 mL). The combined organic extracts were washed with water (2×30 mL), dried over sodium sulfate, concentrated in vacuo and purified by flash chromatography. Elution with hexane:ethyl acetate (1:1) provided the title compound as a solid (0.11 g, 33% yield).1H NMR (CD3OD) δ: 9.14 (s, 1H), 8.04 (d, 2H, J=8.3 Hz), 7.98 (d, 1H, J=3.0 Hz), 7.53-7.68 (m, 3H), 7.34 (d, 2H, J=4.3 Hz), 7.13-7.15 (m, 2H), 7.05-7.07 (m, 2H), 6.98 (d, 1H, J=3.0 Hz), 4.47 (s, 2H), 4.46 (s, 2H), 3.90 (s, 3H). LCMS (API-ES, M+H+): 452.1. (b) 2-Benzyloxy-1,6-dihydrodipyrrolo[3,2-d:3′,4′-b]pyridin-3(2H)-one. To a stirred solution of methyl 1-{[4-(benzyloxy)amino]methyl)}-1-phenylsulfonyl-1H-pyrrolo[2,3-c]pyridine-5-carboxylate (0.11 g, 0.24 mmol) in anhydrous methanol (10 mL) was added sodium ethoxide (0.18 mL, 21 wt % in ethanol, 0.48 mmol). The resulting mixture was stirred for 2 hours at ambient temperature. It was neutralized with excess acetic acid (0.1 mL). On addition of water, the product precipitated out. It was collected by filtration, washed with water and hexane, and dried in vacuo to give a light yellow solid (0.062 g, 91% yield). 1H NMR (DMSO-d6) δ: 12.16 (s, 1H), 8.86 (s, 1H), 7.80 (d, 1H, J=2.6 Hz), 7.52 (d, 2H, J=6.3 Hz), 7.40-7.42 (m, 3H), 6.67 (s, 1H), 5.13 (s, 2H), 4.75 (s, 2H). LCMS (API-ES, M+H+): 280.1. (c) 2-Benzyloxy-6-(2,4-difluoro-benzyl)-1,6-dihydrodipyrrolo[3,2-d:3′,4′-b]pyridin-3(2H)-one. The title compound was prepared by alkylation of 2-benzyloxy-1,6-dihydrodipyrrolo[3,2-d:3′,4′-b]pyridin-3(2H)-one with 2,4-difluorobenzyl bromide in a manner similar to step (a) of example 1. 1H NMR (CD3OD) δ: 8.91 (s, 1H), 7.75 (d, 1H, J=3.0 Hz), 7.51-7.54 (m, 2H), 7.38-7.40 (m, 3H), 7.27-7.29 (m, 1H), 7.02-7.05 (m, 1H), 6.93-7.01 (m, 1H), 6.71 (d, 1H, J=3.0 Hz), 5.64 (s, 2H), 5.18 (s, 2H), 4.65 (s, 2H). LCMS (API-ES, M+H+): 406.1. (d) 6-(2,4-Difluorobenzyl)-2-hydroxy-1,6-dihydrodipyrrolo[3,2-d:3′,4′-b]pyridin-3(2H)-one. To a stirred solution of 2-benzyloxy-6-(2,4-difluorobenzyl)-1,6-dihydrodipyrrolo[3,2-d:3′,4′-b]pyridin-3(2H)-one (0.050 g, 0.12 mmol) in anhydrous ethanol (15 mL) was added palladium hydroxide (5 mg, 20 wt % on carbon). The solution was stirred under a hydrogen atmosphere for 16 h. The catalyst was filtered off and the solution was concentrated until a product precipitated. The product was collected by filtration, washed with water and hexane. Repeated recrystallization from methanol provided the title compound as a light yellow solid (0.002 g, 5.1% yield). 1H NMR (CD3OD) δ: 8.90 (s, 1H), 7.76 (d, 1H, J=3.0 Hz), 7.25-7.29 (m, 1H), 6.99-7.02 (m, 1H), 6.93 (m, 1H), 6.77 (d, 1H, J=3.0 Hz), 5.64 (s, 2H), 5.18 (s, 2H), 4.60 (s, 2H). LCMS (API-ES, M+H+): 316.0. HRMS calcd for C16H12F2N3O2 (M+H) 316.0898, found 316.0897. HPLC: 100% purity.
