Process for the preparation of optically active methionine amide

Abstract

The invention relates to a process for preparing optically active methionine amide in high ee purities in which a mixture of D- and L-methionine amide or the Schiff bases thereof is at least partly converted, optionally in the presence of 0.5-4 equivalents of an aldehyde, relative to the amount of methionine amide, and water, in the presence of an organic solvent, using less than 1.2 equivalents of L- or D-mandelic acid, respectively, relative to the amount of D- or L-methionine amide, respectively, or the Schiff bases thereof, present in the mixture of D- and L-methionine amide or the Schiff bases thereof, into a salt of methionine amide and mandelic acid, a portion consisting substantially of one of the diastereoisomers of the salt is separated from the reaction mixture obtained, and the salt is converted into the optically active methionine. A high degree of optical purity is obtained. This process can be advantageously combined with a preparation of D,L-methionine amide from D,L-methionine nitrile by returning the residual methionine amide obtained after separation of the diastereomeric salt and recovery of the mandelic acid to the preparation of D,L-methionine amide where racemization of the recycled methionine amide takes place in situ. A high overall efficiency can thus obtained in spite of a relatively low efficiency of conversion into the diastereoisomeric salt, relative to the amount of D- and L-methionine amide, or the Schiff bases thereof, used.