0.098 g of sodium borohydride was added to a solution of 1.18 g of 4-acetyl-1-[(2'-t-butoxycarbonylbiphenyl-4-yl)methyl]-2-butylimidazole-5-carbonitrile [prepared as described in step (a) above] in 30 ml of ethanol, and the resulting mixture was stirred at room temperature for 1 hour. The excess sodium borohydride was decomposed by adding acetone, and then the reaction mixture was concentrated by evaporation under reduced pressure. The residue was diluted with an aqueous solution of sodium chloride and extracted with ethyl acetate. The extract was dried and concentrated by evaporation under reduced pressure. The oily residue was purified by column chromatography through silica gel, using a 3:2 by volume mixture of ethyl acetate and hexane as the eluent, to afford 1.18 g of the title compound as a viscous oil.
