4-Bromobenzene-1,2-diamine → 2-(6-bromo-1H-benzimidazol-2-yl)pyrrolidine-1-carboxylic acid tert-butyl ester

Participants

Reaction Conditions

Reaction Steps

A mixture of 4-bromo-benzene-1,2-diamine (2.4 g) and 2-formyl-pyrrolidine-1-carboxylic acid tert-butyl ester (2.55 g) in ethanol (5 mL) was heated in microwave at 80° C. for 1 hour. Mixture was concentrated and purified by flash column chromatography (silica gel, 20 to 80% ethyl acetate/hexane) to give 2-(6-bromo-1H-benzoimidazol-2-yl)-pyrrolidine-1-carboxylic acid tert-butyl ester (2.6 g, yield 55%). LCMS-ESI−: calc'd for C16H20BrN3O2: 366.25. Found: 365.8 (M+H+). 2-[6-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-1H-benzoimidazol-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester: A mixture of 2-(6-bromo-1H-benzoimidazol-2-yl)-pyrrolidine-1-carboxylic acid tert-butyl ester (890 mg, 2.43 mmol), bis(pinacolato)diboron (1.36 g, 5.35 mmol), [1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium(II)(99 mg, 0.12 mmol) and potassium acetate (620 mg, 6.32 mmol) in 15 mL dioxane was heated to 95° C. for 4 hour. The reaction mixture was cooled and dissolved in ethyl acetate and washed with saturated sodium bicarbonate solution. The organic layer dried (MgSO4), concentrated and purified by flash column chromatography (silica gel, 20 to 80% ethyl acetate/hexane) to give 2-(6-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-1H-benzoimidazol-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (588 mg, yield 59%). LCMS-ESI−: calc'd for C32H2OBN3O4: 413.32. Found: 414.0 (M+H+). 2-[2′-(1-Boc-pyrrolidin-2-yl)-3H,3′H-[5,5]bibenzoimidazolyl-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester: A mixture of 2-(6-bromo-1H-benzoimidazol-2-yl)-pyrrolidine-1-carboxylic acid tert-butyl ester (64 mg, 0.174 mmol), 2-[6-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-1H-benzoimidazol-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (72 mg, 0.174 mmol), tetrakis(triphenylphosphine)palladium (30 mg, 0.026 mmol) and potassium carbonate (48 mg, 0.35 mmol) in 2 ml 1,2-dimethoxyethane and 1 mL water was heated to 110° C. in microwave for 15 minutes. The reaction mixture was cooled and dissolved in ethyl acetate and washed with 5% lithium chloride aqueous solution. The organic layer dried (MgSO4), concentrated and purified by flash column chromatography (silica gel, 0 to 10% methanol/ethyl acetate) to give 2-[2′-(1-Boc-pyrrolidin-2-yl)-3H,3′H-[5,5]bibenzoimidazolyl-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (15 mg, yield 15%). LCMS-ESI−: calc'd for C32H40N6O4: 572.70. Found: 573.1 (M+H+). [1-(2-{2′-[1-(2-Methoxycarbonylamino-3-methyl-butyryl)-pyrrolidin-2-yl]-3H,3′H-[5,5]bibenzoimidazolyl-2-yl}-pyrrolidine-1-carbonyl)-2-methyl-propyl]-carbamic acid methyl ester: Trifluoroacetic acid (0.5 mL) was added to (2-[2′-(1-Boc-pyrrolidin-2-yl)-3H,3′H-[5,5]bibenzoimidazolyl-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (15 mg, 0.0262 mmol) and the reaction mixture was stirred at room temperature for 2 hours. The reaction mixture was concentrated and dried overnight under vacuum. The residue was dissolved in DMF (1.5 mL) and to this solution was added 2-Methoxycarbonylamino-3-methyl-butyric acid (10 mg, 0.058 mmol), diisopropylethylamine (27 μL), followed by HATU (20 mg). Reaction mixture was stirred at 0° C. for 60 minutes. The reaction mixture was dissolved in ethyl acetate and washed with dilute sodium bicarbonate solution. The organic layer was dried (MgSO4), concentrated and purified by preparative reverse phase HPLC (GEMINI, 5 to 100% ACN/H2O+0.1% TFA). Product was lyophilized to give [1-(2-{2′-[1-(2-Methoxycarbonylamino-3-methyl-butyryl)-pyrrolidin-2-yl]-3H,3′H-[5,5]bibenzoimidazolyl-2-yl}-pyrrolidine-1-carbonyl)-2-methyl-propyl]-carbamic acid methyl ester as the bis-TFA salt (8.1 mg).

Provenance & Evidence