To a solution of 2-[(4′-Amino-biphenyl-4-carbonyl)-amino]-pentanedioic acid di-tert-butyl ester (350 mg, 0.77 mmol) and 2-Furoic acid (87 mg, 0.77 mmol, 1 equiv.) in DMF (6 mL) was added BOP reagent (409 mg, 0.92 mmol, 1.2 equiv.) and Hunig base (0.16 mL, 0.92 mmol, 1.2 equiv.) under N2. The mixture was stirred at room temperature overnight. Reaction was complete was determined by LC-MS. The reaction mixture was then poured onto cold water. Solid precipitated from the mixture was collected by filtration. The solid was then dissolved in EtOAc, washed with 1N HCl, saturated NaHCO3, and brine, and then dried over MgSO4. After removing the solvent, the solid was dried under vacuum overnight to provide 2-({4′-[(Furan-2-carbonyl)-amino]-biphenyl-4-carbonyl}-amino)-pentanedioic acid di-tert-butyl ester in 87% yield (369 mg). MS (ESI) m/z 549.
