Preparation of (2S,4R)‐2,4‐thiazolidinedicarboxylic acid by separation of diastereoisomeric salts with organic amines

L-Cysteine was condensed with glyoxylic acid monohydrate in acetic acid at 30°C to give (4R)-2,4-thiazolidinedicarboxylic acid [(4R)-TDA] as a mixture of two diastereoisomers, (2R,4R)- and (2S,4R)-TDA. An attempt was made to separate (2S,4R)-TDA from the diastereoisomeric salts of (4R)-TDA with 1-propylamine, 2-methyl-2-propylamine, benzylamine, and (R)- and (S)-1-phenylethylamines [(R)- and (S)-PEA]. The salts of (2S,4R)-TDA were preferentially crystallized as less soluble diastereoisomeric salts. When the salt with (R)-PEA was employed, the separation was successfully achieved to afford optically pure (2S,4R)-TDA in a yield of 41%, based on the starting amount of the diastereoisomeric mixture of (4R)-TDA. Chirality 11:326–329, 1999. © 1999 Wiley-Liss, Inc.