Twenty-first century antiepileptic drugs. An overview of their targets and synthetic approaches

The therapeutic use of the traditional drugs against epilepsy has been hindered by their toxicity and low selectivity. These limitations have stimulated the design and development of new generations of antiepileptic drugs. This review explores the molecular targets and synthesis of the antiepileptic drugs that have entered the market in the 21st century, with a focus on manufacturer synthesis.

Applied biocatalysis beyond just buffers - from aqueous to unconventional media. Options and guidelines

In nature, enzymes conventionally operate under aqueous conditions. Because of this, aqueous buffers are often the choice for reaction media when enzymes are applied in chemical synthesis. However, to meet the demands of an industrial application, due to the poor water solubility of many industrially relevant compounds, an aqueous reaction system will often not be able to provide sufficient substrate loadings. A switch to a non-aqueous solvent system can provide a solution, which is already common for lipases, but more challenging for biocatalysts from other enzyme classes. The choices in solvent types and systems, however, can be overwhelming. Furthermore, some engineering of the protein structure of biocatalyst formulation is required. In this review, a guide for those working with biocatalysts, who look for a way to increase their reaction productivity, is presented. Examples reported clearly show that bulk water is not necessarily required for biocatalytic reactions and that clever solvent systems design can support increased product concentrations thereby decreasing waste formation. Additionally, under these conditions, enzymes can also be combined in cascades with other, water-sensitive, chemical catalysts. Finally, we show that the application of non-aqueous solvents in biocatalysis can actually lead to more sustainable processes. At the hand of flowcharts, following simple questions, one can quickly find what solvent systems are viable.

Simultaneous directed evolution of coupled enzymes for efficient asymmetric synthesis of l-phosphinothricin

The traditional strategy to improve the efficiency of an entire coupled enzyme system relies on separate direction of the evolution of enzymes involved in their respective enzymatic reactions. This strategy can lead to enhanced single-enzyme catalytic efficiency but may also lead to loss of coordination among enzymes. This study aimed to overcome such shortcomings by executing a directed evolution strategy on multiple enzymes in one combined group that catalyzes the asymmetric biosynthesis of l-phosphinothricin. The genes of a glutamate dehydrogenase from Pseudomonas moorei (PmGluDH) and a glucose dehydrogenase from Exiguobacterium sibiricum (EsGDH), along with other gene parts (promoters, ribosomal binding sites (RBSs), and terminators) were simultaneously evolved. The catalytic efficiency of PmGluDH was boosted by introducing the beneficial mutation A164G (from 1.29 s^-1mM^-1 to 183.52 s^-1mM^-1), and the EsGDH expression level was improved by optimizing the linker length between the RBS and the start codon of gdh. The total turnover numbers of the bioreaction increased from 115 (GluDH WT^NADPH) to 5846 (A164G^NADPH coupled with low expression of EsGDH), and to 33950 (A164G^NADPH coupled with high expression of EsGDH). The coupling efficiency was increased from ∼30% (GluDH_WT with low expression of GDH) to 83.3% (GluDH_A164G with high expression of GDH). In the batch production of l-phosphinothricin utilizing whole-cell catalysis, the strongest biocatalytic reaction exhibited a high space-time yield (6410 g·L^-1·d^-1) with strict stereoselectivity (>99% enantiomeric excess).Importance: The traditional strategy to improve multienzyme-catalyzed reaction efficiency may lead to enhanced single-enzyme catalytic efficiency but may also result in loss of coordination among enzymes. We describe a directed evolution strategy of an entire coupled enzyme system to simultaneously enhance enzyme coordination and catalytic efficiency. The simultaneous evolution strategy was applied to a multienzyme-catalyzed reaction for the asymmetric synthesis of l-phosphinothricin, which not only enhanced the catalytic efficiency of GluDH but also improved the coordination between GluDH and GDH. Since this strategy is enzyme-independent, it may be applicable to other coupled enzyme systems for chiral chemical synthesis.

Tuning amino acid dehydrogenases with featured sequences for L-phosphinothricin synthesis by reductive amination

Biosynthesizing unnatural chiral amino acids is challenging due to the limited reductive amination activity of amino acid dehydrogenase (AADH). Here, for the asymmetric synthesis of l-phosphinothricin from 2-oxo-4-[(hydroxy)(methyl)phosphinoyl]butyric acid (PPO), a glutamate dehydrogenase gene (named GluDH3) from Pseudomonas monteilii was selected, cloned and expressed in Escherichia coli (E. coli). To boost its activity, a "two-step"-based computational approach was developed and applied to select the potential beneficial amino acid positions on GluDH3. l-phosphinothricin was synthesized by GluDH-catalyzed asymmetric amination using the d-glucose dehydrogenase from Exiguobacterium sibiricum (EsGDH) for NADPH regeneration. Using lyophilized E. coli cells that co-expressed GluDH3_V375S and EsGDH, up to 89.04 g L^-1 PPO loading was completely converted to l-phosphinothricin within 30 min at 35 °C with a space-time yield of up to 4.752 kg·L^-1·d^-1. The beneficial substitution V375S with increased polar interactions between K90, T193, and substrate PPO exhibited 168.2-fold improved catalytic efficiency (k_cat/K_M) and 344.8-fold enhanced specific activity. After the introduction of serine residues into other GluDHs at specific positions, forty engineered GluDHs exhibited the catalytic functions of "glufosinate dehydrogenase" towards PPO.

Generation of novel family of reductases from PCR based library for the synthesis of chiral alcohols and amines

Biocatalysis has shown tremendous potential in the synthesis of drugs and drug intermediates in the last decade. Screening of novel biocatalysts from the natural genome space is the growing trend to replenish the harsh chemical synthetic routes, commonly used in the pharmaceutical and chemical industry. Here, we report a novel ketoreductase (KERD) and a nitrile reductase isolated from the PCR based library generated from the genome of Rhodococcus ruber and Bacillus subtilis, respectively. Both the proteins are hypothetical in nature as there is no putative homology found in the database, although both the enzymes have significant activity towards the synthesis of chiral alcohols and amines. Enzyme activity over a wide range of substrates (aromatic and aliphatic) for both the novel catalysts was observed. From the unique gene sequence to activity over a broad range of substrate and >99% conversion at higher concentrations (100 mM and above) entitles both the hypothetical enzymes as novel. The novel KERD has shown >99% selectivity for the synthesis of (S)-phenylethanol which makes it a potential candidate for industrial catalysis. The novel nitrile reductase has also shown promising activity for the synthesis of (R)-2-phenylethanolamine, which is a difficult moiety to synthesize chemically. In this report, starting from a homology based library, two highly potent whole cell biocatalysts are obtained.

Efficient biosynthesis of ethyl (R)-4-chloro-3-hydroxybutyrate using a stereoselective carbonyl reductase from Burkholderia gladioli

Background

Ethyl (R)-4-chloro-3-hydroxybutyrate ((R)-CHBE) is a versatile chiral precursor for many pharmaceuticals. Although several biosynthesis strategies have been documented to convert ethyl 4-chloro-3-oxobutanoate (COBE) to (R)-CHBE, the catalytic efficiency and stereoselectivity are still too low to be scaled up for industrial applications. Due to the increasing demand of (R)-CHBE, it is essential to explore more robust biocatalyst capable of preparing (R)-CHBE efficiently.

Results

A stereoselective carbonyl reductase toolbox was constructed and employed into the asymmetric reduction of COBE to (R)-CHBE. A robust enzyme designed as BgADH3 from Burkholderia gladioli CCTCC M 2012379 exhibited excellent activity and enantioselectivity, and was further characterized and investigated in the asymmetric synthesis of (R)-CHBE. An economical and satisfactory enzyme-coupled cofactor recycling system was created using recombinant Escherichia coli cells co-expressing BgADH3 and glucose dehydrogenase genes to regenerate NADPH in situ. In an aqueous/octanol biphasic system, as much as 1200 mmol COBE was completely converted by using substrate fed-batch strategy to afford (R)-CHBE with 99.9 % ee at a space-time yield per gram of biomass of 4.47 mmol∙L⁻¹∙h⁻¹∙g DCW⁻¹.

Conclusions

These data demonstrate the promising of BgADH3 in practical synthesis of (R)-CHBE as a valuable chiral synthon. This study allows for the further application of BgADH3 in the biosynthesis of chiral alcohols, and establishes a preparative scale process for producing (R)-CHBE with excellent enantiopurity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-016-0301-x) contains supplementary material, which is available to authorized users.

Highly enantioselective bioreduction of 1-(3,4-difluorophenyl)-3-nitropropan-1-one: key intermediate of ticagrelor

A simple, highly effective and economical whole-cell mediated process was developed for the biocatalytic reduction of a ketone, intermediate in the synthesis of platelet inhibiting drug ticagrelor.