A solution of KOH (141 mg, 2.52 mmol) in ethanol (2 mL) was added to a solution 2-(6-[N,N-bis(tert-butoxycarbonyl)amino]4-methyl-pyridin-3-ylmethyl)-malonic acid diethyl ester (1.1 g, 2.29 mmol) in ethanol (10 mL) and methylene chloride (4 mL) at 0° C. The mixture was stirred for 18 h at room temperature. The mixture was concentrated under reduced pressure and the residue dissolved in water. Ethyl acetate was added and the organic layer was washed with 0.5 M HCl, water, brine and dried. After filtration and concentration under reduced pressure gave crude 2-(6-[N,N-bis(tert-butoxycarbonyl)-amino]-4-methyl-pyridin-3-ylmethyl)-malonic acid monoethyl ester (1.0 g, 97%).
