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Step 1: 1-Amino-2-propanol (compound 42.1; 3.53 g, 47.0 mmol) and triethylamine (25 mL) were dissolved in methanol (35 mL) under nitrogen protection, and a solution of di-tert-butyl dicarbonate (10.3 g, 47.0 mmol) in methanol (15 mL) was slowly added dropwise. The reaction mixture was stirred at room temperature overnight. Subsequently, the reaction solution was concentrated and the residue was dried under high vacuum to give 8.23 g (quantitative yield) of clear oily product. This oily product was dissolved in tetrahydrofuran (100 mL) and triethylamine (13.1 mL, 94.0 mmol) was added. Methanesulfonyl chloride (3.82 mL, 49.3 mmol) was slowly added dropwise to this solution at 0 °C. After 1 hour of reaction, the reaction mixture was diluted with ethyl acetate and washed sequentially with 1 M aqueous hydrochloric acid, aqueous sodium bicarbonate and saturated saline. The organic phase was dried with anhydrous sodium sulfate and concentrated to give 10.5 g (88% yield) of a clear oily substance (compound 42.2), which solidified after standing. Electrospray mass spectrometry (ES(+)MS) showed m/e = 254 ([M+H]+).

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