May 5, 2003
Volume 81, Number 18
CENEAR 81 18
ISSN 0009-2347

Research in Chiral Fine Chemicals Reaps Recognition

Research collaborators of Degussa and chemists at Avecia were honored recently with national awards.

Pohl Kula
Last December, the German Future Prize was awarded to Maria-Regina Kula and Martina Pohl for outstanding innovation in biocatalyis. Kula and Pohl are, respectively, professor emeritus and visiting professor at Heinrich Heine University, Düsseldorf. They were recognized for work, partially supported by Degussa, that has led to Degussa's economical route to tert-L-leucine. This unnatural amino acid is used as a chiral auxiliary in asymmetric synthesis. It is also a component of some HIV protease inhibitors and matrix metalloprotease inhibitors.

In principle, the amino acid could easily be made by biocatalytic reductive amination of a ketocarboxylic acid precursor. But in practice, the enzyme involved--leucine dehydrogenase (LeuDH)--requires a supply of hydrogen from a cofactor, NADH. The problem is that cofactors like NADH are too expensive for one-time use in manufacturing. Can they be regenerated? Degussa posed the problem to Kula.

The answer lay in an enzyme Kula isolated from yeast, formaldehyde dehydrogenase (FDH). Its reaction degrading formic acid to water and carbon dioxide when coupled to the reduction mediated by LeuDH regenerates NADH for another round of reaction. With Pohl, Kula then developed more active and robust versions of FDH.

Now, Degussa produces tert-L-leucine on a multiton scale based on the NADH-FDH process designed by Kula and Pohl. That process, after further honing at Degussa's Biotechnology Project House, reduced production costs by three orders of magnitude, says Karlheinz Drauz, vice president for technology and R&D management at Degussa. Kula and Pohl "demonstrated for the first time that the use of cofactors in biocatalytic reactions is not prohibitive in terms of either cost or complexity," he adds.

And last March, the U.K. Royal Society of Chemistry presented Avecia the Teamwork in Innovation Award for development of catalysts for asymmetric transfer hydrogenation (CATHy), an effort led by process chemist John Blacker.

CATHy is a rhodium-based catalytic hydrogenation technology for producing chiral amines and chiral alcohols. The catalysts are stable to air and moisture. And reactions are performed at low pressures, precluding the need for special high-pressure vessels. The technology has been scaled up to make several products and is now being developed for a multiton manufacturing process.


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