GB832003A - Steric inversion of allothreonine and intermediates of inversion - Google Patents

Abstract

2 - Aryl - 5 - methyl - D 2 - oxazoline - 4 - carboxylic acids and/or a -aroylamino-b -hydroxybutyric acids are prepared by condensing allothreonine, which may be admixed with threonine, with an aryl nitrile in the presence of an alkaline condensing agent. This agent is conveniently an alkali metal alcoholate, the reaction advantageously being effected in a lower aliphatic alcohol. The nature of the product is stated probably to depend on the length of time that the reaction mixture is allowed to stand and on the other reaction conditions. The invention also comprises the additional step of hydrolysing either product or a mixture thereof with an acid hydrolysing agent to give threonine. In examples: (1) DL-allothreonine containing a small amount of DL-threonine is left to stand for several days with sodium methoxide and benzonitrile, the reaction mixture is diluted with water, unreacted benzonitrile is removed by shaking with benzene, and the aqueous solution is passed through a slightly acid ion-exchanger and then concentrated to give 2-phenyl-5-methyl- D 2-oxazoline - 4 - carboxylic acid; (2) 2 - p - tolyl - 5 - methyl - D 2 - oxazoline - 4 - carboxylic acid is similarly prepared; (3) the reaction mixture of Example (1) is allowed to stand for 9 days, the solvent is distilled off and the residue is left standing for 7 more days before working up as in Example (1) to give DL-N-benzoylthreonine; (4) the product of (1) is heated with dilute hydrochloric acid to give, on working up, DL-threonine; and (5) the product of (3) is heated with dilute sulphuric acid to give, on working up, DL-threonine.