Dimercaptosuccinic acid

Dimercaptosuccinic acid[1]
IUPAC name meso-2,3-dimercaptosuccinic acid
Other names succimer, APRD01236 (Drugbank), Chemet
Identifiers
CAS number	304-55-2 Y
ChemSpider	11285436 Y
UNII	DX1U2629QE Y
EC number	259-952-2
ChEMBL	CHEMBL1201073 N
Jmol-3D images	Image 1
SMILES OC(=O)CC(S)(S)C(=O)O
InChI InChI=1S/C4H6O4S2/c5-2(6)1-4(9,10)3(7)8/h9-10H,1H2,(H,5,6)(H,7,8) Y Key: QOKYAILCOIEKMY-UHFFFAOYSA-N Y InChI=1/C4H6O4S2/c5-2(6)1-4(9,10)3(7)8/h9-10H,1H2,(H,5,6)(H,7,8) Key: QOKYAILCOIEKMY-UHFFFAOYAI
Properties
Molecular formula	C4H6O4S2
Molar mass	182.22 g/mol
Melting point	125 °C, 398 K, 257 °F
N acid (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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

Stereochemistry

The 2,3-dimercaptosuccinic acid molecule has two stereocentres (two asymmetric carbons), and can exist as three different stereoisomers. The 2S,3S and 2R,3R isomers are a pair of enantiomers, whereas the 2R,3S isomer is a meso compound and thus optically inactive.

(2R,3R)-2,3-dimercaptosuccinic acid	(2R,3S)-2,3-dimercaptosuccinic acid (meso-2,3-dimercaptosuccinic acid)	(2S,3S)-2,3-dimercaptosuccinic acid

Preparation and reactivity

DMSA may be prepared by reacting maleic or fumaric acid with sodium thiosulfate followed by hydrolysis.^[2] The dimethyl ester is also known.^[3]

Meso 2,3-dimercaptosuccinic acid binds to "soft" heavy metals such as Hg²⁺ and Pb²⁺, mobilizing these ions for excretion. It binds to metal cations through the thiol groups, which ionize upon complexation.

Medical use

Dimercaptosuccinic acid (CHEMET) is indicated for the treatment of lead poisoning in children with blood level measured above 45 µg/dL. The use of DMSA is not approved for prophylactic/prevention of lead poisoning in anticipation of exposure in known lead contaminated environments. Its elimination half-life is 2.5-3.5 h. DMSA can cross the blood-brain barrier of mice,^[4] but not that of humans, limiting its use to extracting heavy metals from parts of the body other than the central nervous system.^[5][6]

Another application for DMSA is for provocation of tissue heavy metals in anticipation of a urine test. This is sometimes called a "challenge" or "provoked" heavy metals test. DMSA is used to help mobilize heavy metals stored in body tissues (and therefore not typically present in the circulation) and increase the excretion of heavy metals in the urine. In a study by Howard Frumkin et al., this sort of test was shown to not reliably provide an indication of past chronic mercury exposure, something it was often used for.^[7] A 2004 study by GP Archbold, et al. called the results of a DMSA challenge test "misleading" for the purposes of diagnosing mercury toxicity.^[8]

See also

• Chelation therapy
• 2,3-Dimercapto-1-propanesulfonic acid
• EDTA
• Heavy metal poisoning
• Mercury poisoning
• Succinic acid
• DMSA_scan

References

1. ^ Merck Index, 11th Edition, 8854.
2. ^ US 4550193, Lindemann, Martin K. O. & Lukenbach, Elvin R., "Process for the preparation of 2,3-dimercaptosuccinic acid and its lower alkyl esters", assigned to Johnson & Johnson Baby Products 
3. ^ M. Gerecke, E. A. H. Friedheim, A. Brossi (1961). "Zur Kenntnis der 2,3-Dimercapto-bernsteinsäuren". Helvetica Chimca Acta 44 (4): 955–960. doi:10.1002/hlca.19610440410. 
4. ^ Aasath, Jan; Dag Jacobsen, Ole Andersen, Elsa Wickstrøm (March 1995). "Treatment of Mercury and Lead Poisonings with Dimercaptosuccinic Acid (DMSA) and Sodium Dimercaptopropanesulfonate (DMPS)". Analyst 120: 853ff. 
5. ^ Rooney, James (2007). "The role of thiols, dithiols, nutritional factors and interacting ligands in the toxicology of mercury". Toxicology 234 (3): 145–156. doi:10.1016/j.tox.2007.02.016. PMID 17408840. 
6. ^ Guzzi, GianPaolo; Caterina A.M. La Porta (2008). "Molecular mechanisms triggered by mercury". Toxicology 244 (1): 1–12. doi:10.1016/j.tox.2007.11.002. PMID 18077077. 
7. ^ Frumkin H, Manning CC, Williams PL, et al. (February 2001). "Diagnostic chelation challenge with DMSA: a biomarker of long-term mercury exposure?". Environ. Health Perspect. 109 (2): 167–71. doi:10.1289/ehp.01109167. PMC 1240638. PMID 11266328. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1240638. Retrieved 2010-12-20. 
8. ^ Archbold GP, McGuckin RM, Campbell NA (May 2004). "Dimercaptosuccinic acid loading test for assessing mercury burden in healthy individuals". Ann. Clin. Biochem. 41 (Pt 3): 233–6. doi:10.1258/000456304323019622. PMID 15117439. http://acb.rsmjournals.com/cgi/pmidlookup?view=long&pmid=. Retrieved 2010-12-20. 

Further reading

• Aposhian, H.V.; Aposhian, M.M. (1990). "Meso-2,3-dimercaptosuccinic acid: Chemical, pharmacological and toxicological properties of an orally effective metal chelating agent". Annual Review of Pharmacology and Toxicology 30 (1): 279–306. doi:10.1146/annurev.pa.30.040190.001431. PMID 2160791.