3,4-Dimethoxybenzoic acid (400.8 mg, 2.2 mmol), EDC (479 mg, 2.5 mmol) and HOBt (338 mg, 2.5 mmol) were combined in a reaction vial. DMF (2 mL) was added followed by Hunig's base (0.79 mL, 4.5 mmol). The resulting mixture was agitated for 1 hour. Subsequently, 3-methoxycarbonyl-benzyl-ammonium chloride (403.3 mg, 2 mmol) was added and the mixture was agitated 16 h. The reaction mixture was diluted with 10 mL dichloromethane, and the resulting mixture was washed with 1N HCl (2×10 mL), NaHCO3 (satd. aq., 2×10 mL), and brine (1×10 mL), dried, and the solvents were evaporated to give 3-[(3,4-dimethoxy-benzoylamino)-methyl]-benzoic acid methyl ester (680 mg) as an oil which was used without purification. The ester was then dissolved in a mixture of methanol (6 mL) and DMF (1 mL) and treated with Amberlyst® A26 (OH− form) (3730 mg, 5 mmol), and the resulting mixture was agitated for 36 h. The resin was then filtered and washed with 2×4 mL methanol, 1×4 mL DMF and 2×4 mL methanol. The product acid was eluted with a solution of 20% formic acid in methanol. The eluant solvents were evaporated, and the resulting solid was triturated in diethylether. 3-[(3,4-dimethoxy-benzoylamino)-methyl]-benzoic acid was isolated by filtration (386 mg, 61%-2 steps) and carried forward. This intermediate (80 mg, 0.254 mmol) was combined with EDC (57.5 mg, 0.3 mmol) and HOBt (40.5 mg, 0.3 mmol) in a reaction vial, and N-methyl morpholine (0.034 mL, 0.3 mmol) was added. The resulting mixture was agitated for 30 min, after which time, 3-(2-amino-ethyl)-piperidine-1-carboxylic acid tert-butyl ester (64 mg, 0.28 mmol) was added and the resulting mixture was agitated overnight. The reaction mixture was diluted with 3 mL dichloromethane, and the resulting mixture was washed with 1N HCl (2×1 mL), NaHCO3 (satd. aq., 2×1 mL), and brine (1×1 mL), dried, and the solvents were evaporated to 140 mg of the intermediate, 3-(2-{3-[(3,4-dimethoxy-benzoylamino)-methyl]-benzoylamino}-ethyl)-piperidine-1-carboxylic acid tert-butyl ester, which was redissolved in dichloromethane (2 mL). SCX (681 mg, 0.6 mmol) was added and the resulting mixture was agitated overnight. The reaction mixture was filtered and the solids were washed with dichloromethane (2×2 mL) and methanol (2×2 mL). The product was eluted with NH3 in methanol (7N, 3×1 mL). The solvents were evaporated to provide 80 mg (74.3%-2 steps) of the title compound, MS analysis electrospray, 426 (M+H).
