Robert Westphal

Bio: Robert Westphal is an academic researcher from Forschungszentrum Jülich. The author has contributed to research in topics: Phenylacetylcarbinol & Lyase. The author has an hindex of 8, co-authored 18 publications receiving 351 citations.

Engineering stereoselectivity of ThDP‐dependent enzymes

Abstract: Thiamine diphosphate-dependent enzymes are broadly distributed in all organisms, and they catalyse a broad range of C-C bond forming and breaking reactions. Enzymes belonging to the structural families of decarboxylases and transketolases have been particularly well investigated concerning their substrate range, mechanism of stereoselective carboligation and carbolyase reaction. Both structurally different enzyme families differ also in stereoselectivity: enzymes from the decarboxylase family are predominantly R-selective, whereas those from the transketolase family are S-selective. In recent years a key focus of our studies has been on stereoselective benzoin condensation-like 1,2-additions. Meanwhile, several S-selective variants of pyruvate decarboxylase, benzoylformate decarboxylase and 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexene-1-carboxylate (SEPHCHC) synthase as well as R-selective transketolase variants were created that allow access to a broad range of enantiocomplementary α-hydroxyketones and α,α'-dihydroxyketones. This review covers recent studies and the mechanistic understanding of stereoselective C-C bond forming thiamine diphosphate-dependent enzymes, which has been guided by structure-function analyses based on mutagenesis studies and from influences of different substrates and organic co-solvents on stereoselectivity.

A tailor-made chimeric thiamine diphosphate dependent enzyme for the direct asymmetric synthesis of (S)-benzoins.

Abstract: Thiamine diphosphate dependent enzymes are well known for catalyzing the asymmetric synthesis of chiral α-hydroxy ketones from simple prochiral substrates. The steric and chemical properties of the enzyme active site define the product spectrum. Enzymes catalyzing the carboligation of aromatic aldehydes to (S)-benzoins have not so far been identified. We were able to close this gap by constructing a chimeric enzyme, which catalyzes the synthesis of various (S)-benzoins with excellent enantiomeric excess (>99 %) and very good conversion.

Artificial Biocatalytic Linear Cascades for Preparation of Organic Molecules

Abstract: The review compiles artificial cascades involving enzymes with a focus on the last 10 years. A cascade is defined as the combination of at least two reaction steps in a single reaction vessel without isolation of the intermediates, whereby at least one step is catalyzed by an enzyme. Additionally, cascades performed in vivo and in vitro are discussed separately, whereby in vivo cascades are defined here as cascades relying on cofactor recycling by the metabolism or on a metabolite from the living organism. The review introduces a systematic classification of the cascades according to the number of enzymes in the linear sequence and differentiates between cascades involving exclusively enzymes and combinations of enzymes with non-natural catalysts or chemical steps. Since the number of examples involving two enzymes is predominant, the two enzyme cascades are further subdivided according to the number, order, and type of redox steps. Furthermore, this classification differentiates between cascades where al...

Constructing Biocatalytic Cascades: In Vitro and in Vivo Approaches to de Novo Multi-Enzyme Pathways

Abstract: The combination of sequential biocatalytic reactions, via non-natural synthetic cascades, is a rapidly developing field and leads to the generation of complex valuable chemicals from simple precursors. As the toolbox of available biocatalysts continues to expand, so do the options for biocatalytic retrosynthesis of a target molecule, leading to alternative routes employing enzymatic transformations. The implementation of such cascade reactions requires careful consideration, particularly with respect to whether the pathway is constructed in vitro or in vivo. In this Perspective, we describe the relative merits of in vitro, in vivo, and hybrid approaches to building biocatalytic cascades and showcase recent developments in the area. We also highlight the factors that influence the design and implementation of purely enzymatic or chemoenzymatic, one-pot, multistep pathways.