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To a solution of D-alanine methyl ester hydrochloride (5 g, 35.8 mmol) and sodium hydrogen carbonate (9.0 g, 107 mmol) in water (100 mL) was added di-tert-butyl dicarbonate (11.7 g, 53.7 mmol) and the resulting solution was stirred at RTovernight. The reaction mixture was extracted with DCM (3 x 100 mL) and the combined organics were dried over MgSO4, filtered and concentrated under reduced pressure. Crude NMR revealed large amounts of un-reacted di-tert-butyl dicarbonate, hence the material was taken up in DCM (50 mL) and treated with N,N-dimethyl ethylenediamne (5 mL), and stirred for 30 mins. The solution waswashed with 1M HCI (50 mL), dried over MgSO4, filtered and concentrated under reduced pressure to afford 5.35 g (73% yield) of the title compound as a colourless oi I.1H NMR (500 MHz, Chloroform-d) 6 5.04 (5, 1 H), 4.31 (m, 1 H), 3.73 (5, 3H), 1 .44 (5, 9H), 1.37 (d, J = 7.2 Hz, 3H).
17.6 g
With triethylamine; In dichloromethane; at 20 - 25℃; for 24h;
A suspension of D-alanine methyl ester hydrochloride (13.9 g, 100 mmol) in 250 mL of dichloromethane was combined with triethylamine (42 mL, 300 mmol) and di-tert-butyl dicarbonate (24.5 g, 110 mmol). After stirring for 24 hours at ambient temperature, the reaction mixture was combined with 5% NaHaPCL solution and the layers were separated. The organic portion was washed successively with a saturated aqueous sodium bicarbonate solution, a 10% aqueous citric acid solution, water and brine. The organic portion was dried over NaiSCri. filtered and concentrated to give 17.6 g of methyl (2R)-2-[(tert-butoxycarbonyl)amino]propanoate as a colorless oil.
58.0 Parts of D-alanine methyl ester hydrochloride is shaken with 83 parts by volume of a 5 M potassium carbonate solution. The resulting mixture is then extracted three times with portions of methylene chloride. The methylene chloride extracts are combined, dried over anhydrous magnesium sulfate, and stripped to a low volume under reduced pressure. The oily residue is dissolved in a solution of 310 parts of methanol and 200 parts by volume of liquid ammonia and allowed to stand at room temperature for 24 hours. Removal of the solvent under reduced pressure affords an oil, which upon trituration with ethyl ether and cooling, crystallizes. The crystalline material is filtered, dried under vacuum, and recrystallized from isopropyl acetate, to afford D-alanine amide, melting at about 75-80 C.
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