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-a mino acid oxidase in animal kidney, is known to undergo racemization quickl y in solution. The association of (+)- and (-)-2-THC with antimony potassiu m 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 assoc iated ions in acetonitrile/water solution were changing as the racemization progressed. For [Sb-2(L-tart)(2)](2-), the intensities of the associated i ons increased as (+)-2-THC underwent racemization to a (-)-isomer; on the o ther hand, the intensity of the associated ion decreased as (-)-2-THC under went 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. Th e change in the intensities of associated ions can be used for chiral recog nition 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 fr om the consideration of both hydrogen bonding of NH-O functions and HSAB (h ard 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 (C) 2001 John Wile y & Sons, Ltd.