Studies on the association of 2‐thiazolidinecarboxylic acid and antimony potassium tartrate: chiral recognition and prediction of absolute configuration by electrospray ionization mass spectrometry

Optically active 2‐thiazolidinecarboxylic acid (2‐THC), a substrate for D ‐amino acid oxidase in animal kidney, is known to undergo racemization quickly in solution. The association of (+)‐ and (−)‐2‐THC with antimony potassium tartrate K 2 [Sb 2 ( L or D ‐tart) 2 ] was studied by electrospray ionization mass spectrometry (ESI‐MS). We observed that relative intensities of associated ions in acetonitrile/water solution were changing as the racemization progressed. For [Sb 2 ( L ‐tart) 2 ] 2− , the intensities of the associated ions increased as (+)‐2‐THC underwent racemization to a (−)‐isomer; on the other hand, the intensity of the associated ion decreased as (−)‐2‐THC underwent racemization to a (+)‐isomer. In the case of [Sb 2 ( D ‐tart) 2 ] 2− , an opposite effect on the intensities of the associated ions was observed. The change in the intensities of associated ions can be used for chiral recognition of (+)‐2‐THC and (−)‐2THC. Stereochemical models of the association of the optical isomers with [Sb 2 ( L ‐ or D ‐tart) 2 ] 2− were constructed from the consideration of both hydrogen bonding of NH‐O functions and HSAB (hard and soft acids and bases) interaction of S and Sb atoms. Comparison of the stereochemical models with the ESI‐MS results enabled us to predict the absolute configurations of the 2‐THC isomers. Copyright © 2001 John Wiley & Sons, Ltd.