Metal complexes are widely used as catalysts for the synthesis of drugs, particularly single enantiomer or chiral compounds. However, one of the problems associated with them is that the catalysts need to be carefully recovered, in order to prevent toxic residues from contaminating the bulk active ingredient.
One solution has been to bind the catalysts to a solid phase, which renders the metal complexes immobile and allows the drug to be flushed out of the reaction vessel, leaving the catalyst behind. However, there is a trade-off with this approach, as the binding the catalysts to the solid phase can often cause reduced efficiency in the reaction, cutting into yields as the mixing of the reagents and catalyst is reduced.
Another problem with current solid phase technologies is that they can be hard to remove by filtration, adding to the fuss and cost of purifying the drug product.
Aiguo Hu and colleagues from the University of North Carolina in the US have solved this problem by binding a ruthenium catalyst - used for the production of aromatic ketones (a widely-used pharmaceutical building block) onto magnetic nanoparticles.
Once the reaction had taken place, the researchers were able to easily recycle the catalysts by applying magnets to the vessel, tilting it and decanting off the reagents. Using this approach, they were able to reuse the catalysts for up to 14 times, without loss of activity and the ability of the catalysts to produce the desired enantiomer.
This approach "should allow the design of other superparamagnetic nanoparticle-supported asymmetric catalysts for a wide range of organic transformations," according to the authors.
The study is published in the current edition of the Journal of the American Chemical Society. For more information, visit the JACS website.