Chemical design made easier

Rice University scientists prepare elusive organocatalysts for drug and fine chemical synthesis

Rice University scientists using an efficient metal-free process have synthesized dozens of small-molecule catalysts, tools that promise to speed the making of novel chemicals, including drugs.

The lab of synthetic chemist László Kürti made elusive chiral biaryl compounds in a single-flask process that does not require the use of transition metals.

These biaryls are called organocatalysts because they catalyze chemical reactions without metal ions. They eliminate the need for transition metals and simplify chemical processes to synthesize new molecules. Transition metals are conductive metals that include titanium, iron, nickel, silver, copper, palladium and gold and are commonly used in catalysis.

The new tools detailed in the Angewandte Chemie international edition open avenues for faster and more cost-effective chemical synthesis, Kürti said.

Biaryls are molecular compounds of two aromatic rings directly joined by a carbon-carbon bond. When functionalized, or altered, these biaryls (phenyl-phenyl, naphthyl-phenyl, thienyl-naphthyl and more) become highly selective, reliable and customizable catalysts, Kürti said.

Kürti’s research uses biaryls as catalysts to develop novel single-enantiomer compounds.

Enantiomers are asymmetrical molecules found among organic compounds. Like one’s hands, their structures are mirror images that cannot be superimposed on each other. Significantly, these twins can have radically different effects – one beneficial, one not — as they interact with enzymes, proteins, receptors and even other chiral catalysts. Pharmaceutical companies understandably want to make drugs that contain only the helpful enantiomer.

Currently, single-enantiomer compounds are painstakingly synthesized as building blocks for drugs, agricultural products and functional materials.

Kürti said that by decade’s end, 95 percent of chiral drugs will be sold as single enantiomers. But synthesizing one particular enantiomer with precision and high efficiency is hard, especially via trial-and-error approaches that to now often require transition metal catalysts.

“For enantiomer preparations, you need catalysts,” he said, but transition metals are expensive and can leave toxic residues that need to be removed before the compound can be used in clinical trials. The Rice lab’s simple, cost-effective way to make chiral-functionalized biaryls not only eliminates the need for transition metals but can replace many steps in the synthesis process. Each step can take days or weeks.

Read more: Chemical design made easier

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