Parting twins

Cooperative catalysis ensures the beneficial chiral product

 
By Shrutika Mathur
Last Updated: Saturday 04 July 2015

Thalidomide,  a drug used during the 1950s as a sleeping pill and to relieve morning sickness in pregnant women, was a mixture of two forms: one beneficial, while the other caused severe birth defects. Chemists handing out the drug did not know this.

A chemical compound if visualized three-dimensionally can exist in two forms—mirror images. Chirality, from the Greek word cheira, or ‘hand’, is the name given to this property. As a drug, one twin could be good to the body and the other, bad. Studies have been directed towards methods of production of the good forms. Catalysts that speed up the reaction do not ensure production of the good form. A research published in the February 19 issue of Science suggests cooperative catalysis: two catalysts are used such that one ensures the speed and the other gives the reaction a direction. Hao Xu and colleagues from department of chemistry and chemical biology at Harvard University in USA added urea with thiourea in cooperative catalysis and procured the beneficial form of tetrahydroquinoline, an antioxidant and antibacterial drug.

Chiral catalysis, which directs a reaction towards production of the favourable mirror image, is not new but has been expensive so far and produces harmful by-products. The antibiotic penicillin is a chiral product that would benefit from cooperative catalysis.

“This method is environment friendly as the catalyst is a non-metal and recyclable,” said Eric Jacobsen who led the study. Organic chemist Peter Schreiner at Justus-Liebig University in Germany said in a comment on the study: “This is likely to become a general strategy for asymmetric catalysis.”

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