Haloalkane dehalogenase catalysed desymmetrisation and tandem kinetic resolution for the preparation of chiral haloalcohols

Synthesis of Optically Active syn- and anti-Chlorohydrins through a Bienzymatic Reductive Cascade

A bienzymatic cascade has been designed and optimized to obtain enantiopure chlorohydrins starting from the corresponding 1-aryl-2-chlorobut-2-en-1-ones. For the synthesis of these α-chloroenones, a two-step sequence was developed consisting of the allylation of the corresponding aldehyde with 3-dichloroprop-1-ene, followed by oxidation and further isomerization. The selective cooperative catalytic system involving ene-reductases (EREDs) and alcohol dehydrogenases (ADHs) afforded the desired optically active chlorohydrins under mild reaction conditions in excellent conversions (up to >99%) and selectivities (up to >99:1 diastereomeric ratio (dr), >99% enantiomeric excess (ee)).

Metagenome-derived haloalkane dehalogenases with novel catalytic properties

Haloalkane dehalogenases (HLDs) are environmentally relevant enzymes cleaving a carbon-halogen bond in a wide range of halogenated pollutants. PCR with degenerate primers and genome-walking was used for the retrieval of four HLD-encoding genes from groundwater-derived environmental DNA. Using specific primers and the environmental DNA as a template, we succeeded in generating additional amplicons, resulting altogether in three clusters of sequences with each cluster comprising 8-13 closely related putative HLD-encoding genes. A phylogenetic analysis of the translated genes revealed that three HLDs are members of the HLD-I subfamily, whereas one gene encodes an enzyme from the subfamily HLD-II. Two metagenome-derived HLDs, eHLD-B and eHLD-C, each from a different subfamily, were heterologously produced in active form, purified and characterized in terms of their thermostability, pH and temperature optimum, quaternary structure, substrate specificity towards 30 halogenated compounds, and enantioselectivity. eHLD-B and eHLD-C showed striking differences in their activities, substrate preferences, and tolerance to temperature. Profound differences were also determined in the enantiopreference and enantioselectivity of these enzymes towards selected substrates. Comparing our data with those of known HLDs revealed that eHLD-C exhibits a unique combination of high thermostability, high activity, and an unusually broad pH optimum, which covers the entire range of pH 5.5-8.9. Moreover, a so far unreported high thermostability for HLDs was determined for this enzyme at pH values lower than 6.0. Thus, eHLD-C represents an attractive and novel biocatalyst for biotechnological applications.

Regio- and Enantioselective Sequential Dehalogenation of rac-1,3-Dibromobutane by Haloalkane Dehalogenase LinB

The hydrolytic dehalogenation of rac-1,3-dibromobutane catalyzed by the haloalkane dehalogenase LinB from Sphingobium japonicum UT26 proceeds in a sequential fashion: initial formation of intermediate haloalcohols followed by a second hydrolytic step to produce the final diol. Detailed investigation of the course of the reaction revealed favored nucleophilic displacement of the sec-halogen in the first hydrolytic event with pronounced R enantioselectivity. The second hydrolysis step proceeded with a regioselectivity switch at the primary position, with preference for the S enantiomer. Because of complex competition between all eight possible reactions, intermediate haloalcohols formed with moderate to good ee ((S)-4-bromobutan-2-ol: up to 87 %). Similarly, (S)-butane-1,3-diol was formed at a maximum ee of 35 % before full hydrolysis furnished the racemic diol product.

Mohangic Acids A-E, p-Aminoacetophenonic Acids from a Marine-Mudflat-Derived Streptomyces sp

Mohangic acids A-E (1-5) were isolated from a marine Streptomyces sp. collected from a mudflat in Buan, Republic of Korea. Comprehensive spectroscopic analysis revealed that the mohangic acids are new members of the p-aminoacetophenonic acid class. The relative and absolute configurations of the mohangic acids were determined by J-based configuration analysis and by the application of bidentate chiral NMR solvents followed by (13)C NMR analysis, chemical derivatization, and circular dichroism spectroscopy. Mohangic acid E (5), which is the first glycosylated compound in the p-aminoacetophenonic acid family, displayed significant quinone reductase induction activity.

Computational library design for increasing haloalkane dehalogenase stability

We explored the use of a computational design framework for the stabilization of the haloalkane dehalogenase LinB. Energy calculations, disulfide bond design, molecular dynamics simulations, and rational inspection of mutant structures predicted many stabilizing mutations. Screening of these in small mutant libraries led to the discovery of seventeen point mutations and one disulfide bond that enhanced thermostability. Mutations located in or contacting flexible regions of the protein had a larger stabilizing effect than mutations outside such regions. The combined introduction of twelve stabilizing mutations resulted in a LinB mutant with a 23 °C increase in apparent melting temperature (Tm,app , 72.5 °C) and an over 200-fold longer half-life at 60 °C. The most stable LinB variants also displayed increased compatibility with co-solvents, thus allowing substrate conversion and kinetic resolution at much higher concentrations than with the wild-type enzyme.

Draft genome sequence of Rhodococcus rhodochrous strain ATCC 17895

Rhodococcus rhodochrous ATCC 17895 possesses an array of mono- and dioxygenases, as well as hydratases, which makes it an interesting organism for biocatalysis. R. rhodochrous is a Gram-positive aerobic bacterium with a rod-like morphology. Here we describe the features of this organism, together with the complete genome sequence and annotation. The 6,869,887 bp long genome contains 6,609 protein-coding genes and 53 RNA genes. Based on small subunit rRNA analysis, the strain is more likely to be a strain of Rhodococcus erythropolis rather than Rhodococcus rhodochrous.

Inverting hydrolases and their use in enantioconvergent biotransformations

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Enantioconvergent processes overcome the 50%-yield limits of kinetic resolution.

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Inverting enzymes are key catalysts for enantioconvergent processes.

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Enzyme engineering provided improved variants of inverting enzymes.

Owing to the more abundant occurrence of racemic compounds compared to prochiral or meso forms, most enantiomerically pure products are obtained via racemate resolution. This review summarizes (chemo)enzymatic enantioconvergent processes based on the use of hydrolytic enzymes, which are able to invert a stereocenter during catalysis that can overcome the 50%-yield limitation of kinetic resolution. Recent developments are presented in the fields of inverting or retaining sulfatases, epoxide hydrolases and dehalogenases, which allow the production of secondary alcohols or vicinal diols at a 100% theoretical yield from a racemate via enantioconvergent processes.