The general procedure for the synthesis of D-alaninamide hydrochloride from ammonia, (tert-butoxycarbonyl)alanine and ethyl chloroformate is as follows:
1. Boc-D-alanine (5.0 g, 26.43 mmol) was dissolved in anhydrous THF (100 mL).
2. triethylamine (4 mL, 2.91 g, 28.76 mmol) was added to the solution, followed by slow dropwise addition of ethyl chloroformate (2.5 mL, 2.951 g, 27.19 mmol).
3. The reaction mixture was placed in a carbon tetrachloride/dry ice cold bath with continuous stirring for about 30 minutes.
4. Concentrated ammonium hydroxide solution (5 mL, 74.0 mmol) was added, then the reaction mixture was transferred to a refrigerator and allowed to stand overnight.
5. Upon completion of the reaction, the solvent was removed by vacuum evaporation and the residue was dissolved in ethyl acetate.
6. The ethyl acetate layer was washed using saturated sodium carbonate solution and water, followed by drying the organic phase with anhydrous magnesium sulfate.
7. The desiccant was removed by filtration and the solvent was evaporated to obtain the crude product.
8. The crude product was treated with saturated hydrochloric acid/dioxane solution for 1 hour at room temperature.
9. The dioxane was removed by vacuum evaporation and the residue was dissolved in a small amount of methanol and precipitated by the addition of ether to give D-alaninamide hydrochloride (2.5 g, 76% yield).
