The characteristic of DL-tyrosine ethyl ester resolution by optically active L-tartaric acid in ethanol was researched. Tartaric acid, tartaric acid monotyrosine ethyl ester salt and tartaric acid dityrosine ethyl ester salt existed in ethanol solution simultaneously, and the equilibrium of the three materials played an important role in resolution results. The configuration of resolved tyrosine was affected by the molar ratio of L-tartaric acid to DL-tyrosine ethyl ester. If the former was more than the latter, more D-tyrosine was produced than L-tyrosine, but if the former was less than the latter, more L-tyrosine was produced, and if both were equal, racemic DL-tyrosine was produced. Deeper research on the characteristic of diastereomeric crystallization of D-tartaric acid, L-tartaric acid and L-tyrosine ethyl ester in different molar ratio, revealed the special property of this resolution process. Because of the low solubility of tartaric acid diL- or D-tyrosine ethyl ester salt in ethanol, the optically pure D-tyrosine could not be prepared through resolving tyrosine ethyl ester by tartaric acid. However, through forming the tartaric acid dityrosine methyl ester diastereomeric salt in methanol, the D-tyrosine was prepared successfully with 99.0% optical purity.

Key words: tartaric acid, tyrosine, resolution, tartaric acid dityrosine methyl ester salt, tyrosine ethyl ester, tyrosine methyl ester