A suspension of 940 mg (2.0 mMol) of tert.-butyl 4'-[(2-n-propyl-6-carboxy-benzimidazol-1-yl)-methyl]biphenyl-2-carboxylate and 320 mg (2.0 mMol) of carbonyldiimidazole in a solution of 1.0 ml of triethylamine in 30 ml of tetrahydrofuran is stirred for 30 minutes at ambient temperature, then 250 mg (2.0 mMol) of 2-methylaminoaniline are added and the mixture is stirred for a further 16 hours. It is then evaporated to dryness and the residue is refluxed in 20 ml of phosphorus oxychloride, with stirring, for 1 hour. The majority of the phosphorus oxychloride is then distilled off, the dark, greasy residue is decomposed with 30 ml of water, the strongly acidic suspension thus obtained is refluxed for about 1 hour, adjusted to pH 6 after cooling and then concentrated by evaporation. The crude product obtained is purified by column chromatography (120 g of silica gel, eluant: methylene chloride/methanol=15:1).
