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

Abstract

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.