To a mixture of 2-(methylamino)ethanol (41 mg), sodium triacetoxyborohydride (166 mg), acetic acid (9 mg), and dichloromethane (4 ml) was added tert-butyl (2-{[(4′-formylbiphenyl-3-yl)methyl](methyl)amino}-2-oxoethyl)carbamate (200 mg), followed by stirring for 5 hours. To the reaction mixture was added CHCl3-saturated aqueous sodium hydrogen carbonate solution, the organic layer was dried over Na2SO4, and then the solvent was evaporated. The obtained residue was purified by silica gel column chromatography (3% MeOH/chloroform) to obtain tert-butyl (2-{[(4′-{[(2-hydroxyethyl)(methyl)amino]methyl}biphenyl-3-yl)methyl](methyl)amino}-2-oxoethyl)carbamate (230 mg) as a colorless oil.
