Resolution of Amino Acids. IX. Studies on the Preparation of β-Hydroxyasparagines and Configuration of Natural Hydroxyasparagine

Crystalline threo-and erythro-β-hydroxy-l-asparagine were prepared via asymmetric hydrolysis of the corresponding hydroxy-l-aspartic acid diamide by leucine aminopeptidase. The isomers of hydroxy-l-asparagine obtained were compared with the natural hydroxyasparagine isolated from human urine with respect to optical rotation and chromatography. From the results it is concluded that the spacial configuration of the natural product is that of erythro-β-hydroxy-l-asparagine. Additional studies were also carried out to prepare threo- and erythro-β-hydroxy-Dl-asparagine from the corresponding hydroxy-Dl-aspartic acid diamide without the enzyme.