2-Bromo-4-fluorobenzenesulfonyl chloride (0.584 g) was added to a solution of ethyl 3-(2,4-diamino-3-methoxycarbonylphenyl)-furan-2-carboxylate (Intermediate 89, 0.650 g) in DCM (30 mL) and pyridine (10 mL). The resultant mixture was stirred at room temperature for 45 minutes. A further amount of 2-bromo-4-fluorobenzene-sulfonyl chloride (0.584 g) was added and the mixture stirred for a further 1 hour. A further amount of 2-bromo-4-fluorobenzenesulfonyl chloride (0.300 g) was added and the mixture stirred for a further 30 minutes. The mixture was concentrated in vacuo and the residue was partitioned between water and DCM. The organic layer was dried (MgSO4), filtered and the filtrate was concentrated in vacuo. The residue was triturated with methanol and the resultant solid was collected by filtration and air dried to give ethyl 3-[2-amino-4-(2-bromo-4-fluorobenzenesulfonylamino)-3-methoxycarbonylphenyl]-furan-2-carboxylate (0.960 g) as a powder.
