The acylation of 4-amino-3-methylbenzoic acid methyl ester (I) with butyryl chloride (II) in hot chlorobenzene gives the corresponding amide (III), which is nitrated with HNO3/H2SO4 yielding 4-butyramido-3-methyl-5-nitrobenzoic acid methyl ester (IV). The hydrogenation of (IV) with H2 over Pd/C in methanol affords the expected amino compound (V), which is cyclized in refluxing acetic acid to 2-propyl-4-methylbenzimidazole-6-carboxylic acid methyl ester (VI). The hydrolysis of (VI) with NaOH in refluxing methanol/water affords the corresponding free acid (VII), which is cyclized with N-methyl-o-phenylenediamine (VIII) by means of polyphosphoric acid (PPA) at 150 C, giving 4-methyl-6-(1-methylbenzimidazol-2-yl)-2-propylbenzimidazole (IX). The condensation of (IX) with 4'-(bromomethyl)biphenyl-4-carboxylic acid tert-butyl ester (X) by means of potassium tert-butoxide in DMSO yields the tert-butyl ester (XI), which is finally hydrolyzed with trifluoroacetic acid.