Further studies on β-hydroxyaspartic acid

Stability studies with the two diastereoisomers of β-hydroxyaspartic acid have demonstrated that heating of either the erythro or the threo isomer in 6 N HCl at 120°C. leads to an equilibrium mixture of the two forms. After 96 hours a ratio of 5:2 of the erythro to the threo isomer is established. When either diastereoisomer is heated in water at 120°C., partial deamination and cleavage to glycine is observed as well as the interconversion of both compounds. The threo - predominates over erythro -β-hydroxyaspartic acid in a ratio of 2:1 after 50 hours of heating. The possible occurrence of β-hydroxyaspartic acid in several proteins has been investigated. Even though a component having the same chromatographic properties as erythro -β-hydroxyaspartic acid has been found in the protein hydrolysates, it has failed to react positively in other tests characteristic of β-hydroxyaspartic acid.