A COMPARATIVE-STUDY OF MESO-2,3-DIMERCAPTOSUCCINIC AND RAC-2,3-DIMERCAPTOSUCCINIC ACIDS AND THEIR ZINC-COMPLEXES IN AQUEOUS-SOLUTION

The conformations of meso-2,3-dimercaptosuccinic acid (meso-DMSA) in a queous solution have been postulated from proton NMR titrations. The c omplexes formed with zinc(II) and the ligands rac-DMSA and meso-DMSA h ave been postulated from potentiometric titrations of solutions contai ning varying ratios of zinc:ligand. The complex formation behavior of rac-DMSA with zinc(II) is dramatically different from that of meso-DMS A. These differences are reflected in the complex formation constants of the zinc(II) species and their distributions in solution as a funct ion of zinc:ligand ratios and as a function of pH. On the basis of the se results we have predicted that rac-DMSA is more effective than meso -DMSA in mobilizing lead in vivo and that the 1:2 zinc complex of rac- DMSA can be used effectively for the treatment of heavy metal poisonin g because endogenous zinc will not be depleted by this chelation treat ment.