Subsequently, to a solution of (N-t-butoxycarbonyl-N-methyl-amino)acetic acid (2.52 g, 13.3 mmol) and p-nitrobenzyl alcohol (4.07 g, 26.6 mmol) in methylene chloride (125 ml) were added WSC (5,10 g, 26.6 mmol) and 4-dimethylaminopyridine (252 mg, 1.33 mmol) in an ice bath under an atmosphere of nitrogen, and the mixture was stirred at room temperature overnight. After checking the completion of the reaction, the reaction mixture was partitioned between ethyl acetate and saturated aqueous sodium chloride solution. The organic layer was dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The residue was purified by chromatography on a silica gel column using hexane:ethyl acetate (1:1) as the eluant to afford (N-t-butoxycarbonyl-N-methyl-amino)acetic acid p-nitrobenzyl ester (4.30 g, yield 88%) as a pale yellow oil.
