Haloalkane dehalogenases in biocatalysis kinetic resolution and beyond

PhD ceremony: Ms. A. Westerbeek, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Haloalkane dehalogenases in biocatalysis kinetic resolution and beyond

Promotor(s): prof. D.B. Janssen, prof. B.L. Feringa

Faculteit: Wiskunde en Natuurwetenschappen

Haloalkane dehalogenases are a group of enzymes that catalyse the cleavage of a carbon-halogen bond in haloalkanes, producing the respective alcohols. First isolated by Groningen scientists in the 1980s, these enzymes accept many different molecules as substrates. Some of their (putative) applications lie for instance in the treatment of polluted groundwater, or in the recycling of side products generated in the industrial synthesis of various bulk chemicals. Because of their wide substrate scope and enantioselectivity these proteins are interesting targets for white biotechnology as well. These enzymes can function as biocatalysts for the production of expensive enantiopure building blocks in for instance medicinal chemistry.

The research summarised in this thesis describes enantioselective conversion of various compounds, such as alpha - haloamides and a - haloesters by haloalkane dehalogenases. The chiral substrates are converted often with high E-values, producing only one of the enantiomers of the respective alcohols, yet with inversion of configuration. The high enantioselectivities with a - haloamides were investigated and explained by MD-simulations. A standard kinetic resolution process results in a maximal yield of 50% substrate and 50% product. To overcome these 50% yields, substrate was racemised in situ by a non-toxic polymer to generate a dynamic kinetic resolution process with yields up to 78% of alpha - hydroxyamides. Furthermore, an enantioconvergent process, combining kinetic resolution and follow-up chemical reactions, resulted in high yields of up to 98% of various enantiopure N- O- and S-substituted amides. In summary, this thesis shows that haloalkane dehalogenases can indeed be employed for the production of interesting enantiopure chemicals.