To a mixture of 2-n-propyl-4-(2-aminoethyl)-1-[2'-(1-trityl-1H-tetrazol-5-yl)biphenyl-4-yl)methylimidazole (21.95 g) and tetrahydrofuran (200 ml) is added a solution of ethyl glyoxylate hydrate (4.25 g) in tetrahydrofuran (20 ml) at 5° C. The mixture is stirred overnight at room temperature and refluxed for 30 minutes. To a mixture is added a 8% hydrogen chloride ethanol solution (100 ml) at room temperature. The reaction mixture is stirred for 30 minutes, then evaporated. The residue is dissolved in chloroform and washed successively with a saturated sodium hydrogen carbonate solution and brine. The organic layer is dried and evaporated. The oxalate is recrystallized from ethanol to give ethyl 2-n-propyl-3-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl-4,5,6,7-tetrahydroimidazo[4,5-c]pyridine-4-carboxylate oxalate (10.84 g).
