Succimer

Dimercaptosuccinic acid, or DMSA, is the chemical compound with the formula HO2CCH(SH)CH(SH)CO2H. This colourless solid contains two carboxylic acid and two thiol groups, the latter being responsible for the mildly unpleasant odour of this dicarboxylic acid. It occurs in two diastereomeric forms, meso and the chiral dl forms. The meso isomer is used as a chelating agent.

Preparation
DMSA may be prepared by reacting acetylene dicarboxylic acid with sodium thiosulfate followed by hydrolysis.

Chelating agent
Meso 2,3-dimecaptosuccinic acid is used to sequester heavy metals such as mercury and lead for excretion. DMSA can cross the blood-brain barrier of mice. but it cannot cross the BBB of humans and so it is not useful for extracting heavy metals from the brain of humans

DMSA is also called succimer and is sold under the brand name Chemet. The dimethyl ester is also known.