Making Nobel-winning chemistry reaction even better

Making a Nobel-winning chemistry reaction even better

12:33 AM, 8th November 2011
Making a Nobel-winning chemistry reaction even better


CAMBRIDGE, US: In 2005, MIT Professor Richard Schrock won the Nobel Prize in chemistry for developing catalysts for a reaction that is widely used to produce pharmaceuticals, fuels and other synthetic chemicals. That reaction, known as olefin metathesis, involves breaking and making double bonds between carbon atoms to produce new types of carbon-carbon double bonds.

One limitation to the metathesis reaction is that it had not been possible to control the configuration of the olefin products, which can occur in one of two configurations. However, Schrock and his Collaborator Amir Hoveyda at Boston College have now developed a catalyst that yields almost exclusively the more desirable configuration, known as cis.

In a paper appearing in the November 3 issue of Nature, the researchers reported using their new catalyst to generate the cis form of two natural compounds that have been of great interest to scientists because of their potential as cancer drugs. They expect that the catalyst, which contains tungsten, could also be useful for controlling the configuration of hundreds of other natural products.

Lead authors of the paper are Miao Yu, a graduate student in Hoveyda’s lab, and Chenbo Wang, a Postdoc at Boston College. Oxford University researchers Andrew Kyle, Pavol Jakubec and Darren Dixon are also authors of the paper.

In the Nature paper, the researchers focused on synthesizing macrocycles. Compounds of this type often have potent biological activity, making them useful as drugs, said Hoveyda, Professor of chemistry and Principal Author of the paper.

The researchers were able to synthesize two naturally occurring macrocycles, epothilone and nakadomarin. Both compounds can be made in about 16 chemical steps, the last of which is a metathesis closing of the ring through formation of a double bond between two carbon atoms. Metathesis requires a catalyst - a special compound that consists of a metal atom attached to one or more organic structures known as ligands.

The cis configuration is found in most naturally occurring compounds. Hoveyda speculates that the cis configuration might be better able to interact with biological structures. Unfortunately, most metathesis reactions produce a mixture of cis and trans. Mixtures of cis and trans products are very difficult to separate.

The team’s new catalyst steers the reaction toward predominantly the cis form. Using this catalyst, the researchers were able to generate cis configuration of epothilone and nakadomarin more than 95 per cent of the time. “It turns out to be a surprisingly efficient solution, but nobody’s ever done it before,” said Schrock.

Also tungsten is more abundant than ruthenium, which is a precious metal used in other, more popular metathesis catalysts. Schrock and Hoveyda have started a company called XiMo to work with companies that synthesize drugs or other chemicals such as polymers, pesticides and fragrances, to develop new catalysts to make their production processes more efficient.

(C) Massachusetts Institute of Technology News




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