General procedure for the synthesis of N-Boc-O-methyl-L-serine from O-methyl DL-serine and di-tert-butyl dicarbonate: 35 mL of aqueous 1 N sodium hydroxide solution and 35 mL of tetrahydrofuran (THF) were added to 2.0 g (17 mmol) of O-methyl DL-serine. With stirring at 0 °C, a solution of di-tert-butyl dicarbonate (4.03 g, 18.5 mmol) in THF (15 mL) was added slowly. The reaction mixture was stirred at room temperature overnight. Upon completion of the reaction, the reaction mixture was concentrated by evaporation under reduced pressure. The aqueous phase was acidified to pH 4-5 with 10% aqueous citric acid and then extracted with ethyl acetate. The organic phase was washed with saturated brine, dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure to give 3.6 g of N-Boc-O-methyl-L-serine (98% yield). Mass spectrum (ESI) m/z: 220.1 (M + H)+.
