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Step 1: Synthesis of 3-(tert-butoxycarbonyl(methyl)amino)propionic acid 1. a mineral oil suspension of 60% NaH (0.528 g, 13.21 mmol) was washed with hexane (2 x 10 mL) to remove the mineral oil. 2. The washed NaH was suspended in anhydrous THF (6 mL) and the mixture was cooled to 0°C. 3. A solution of Boc-β-alanine (1 g, 5.29 mmol) in anhydrous THF (6 mL) was slowly added with stirring. 4. After 5 min, anhydrous THF (6 mL) solution of iodomethane (0.823 mL, 13.21 mmol) was added dropwise. 5. The reaction mixture was stirred overnight at 0 °C to room temperature. 6. Upon completion of the reaction, the reaction was quenched with ice-cold deionized water (50 mL) and the mixture was washed with ether (25 mL). 7. Separate the aqueous layer and acidify to pH < 2 with concentrated aqueous hydrochloric acid (3 mL). 8. Extract the acidified aqueous layer with ethyl acetate (3 x 20 mL). 9. Combine the organic phases, dry with anhydrous sodium sulfate and concentrate under reduced pressure to afford the target product N-Boc-3-(methylamino)propionic acid (1.095 g, quantitative yield) as a yellow oil.