Dichloromethane → (N,N-diethylcarbamoyl)methyl methyl (2E)but-2-ene-1,4-dionate

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As an example of the one-pot procedure for preparing crystalline (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate mesylate, a solution of (2R)-2-phenylcarbonyloxypropyl (2S)-2-(tert-butoxycarbonyl)amino-3-(3,4-dihydroxyphenyl)propanoate in a solvent in which it is soluble is prepared. Examples of suitable solvents include dichloromethane and dioxane. The tert-butoxycarbonyl group is deprotected by adding an acid to provide (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate acid salt. Suitable acids are not limited to volatile acids. Examples of suitable acids for deprotecting the tert-butoxycarbonyl group include hydrochloric acid, methanesulfonic acid, trifluoroacetic acid, and hydrogen bromide. After deprotection, the first solvent can be removed and water added to the (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate acid salt. The (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate acid salt can be neutralized with a base such as NaHCO3 or KHCO3 to provide (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate. (2R)-2-Phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate can then be extracted with a second solvent such as methyl tert-butylether, dichloromethane, ethylacetate, or a mixture of ethylacetate and isopropanol. Methanesulfonic acid can be added to the extracted (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate to convert the (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate to crystalline (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate mesylate. Crystalline (2R)-2-phenylcarbonyloxypropyl (2S)-2-amino-3-(3,4-dihydroxyphenyl)propanoate mesylate can then be isolated from the second solvent by filtration.

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