Coevolution of the Activity and Thermostability of an ϵ-Keto Ester Reductase for Better Synthesis of an (R)-α-Lipoic Acid Precursor

Structure-Guided Engineering of Carbonyl Reductase LbCR to Simultaneously Enhance Catalytic Activity and Thermostability toward Bulky Ketones

(S)-2-Chloro-1-(2,4-dichlorophenyl)ethanol ((S)-TCPE) is an important building block for the synthesis of antifungal drug luliconazole. Herein, a carbonyl reductase (CR) from Levilactobacillus brevis (LbCR) was identified for synthesis of (S)-TCPE. Through comprehensive Ala scanning and site-saturated mutagenesis (SSM) targeting the residues surrounding the substrate-binding pocket, the "best" variant LbCRM4 (N96V/E145A/A202L/M206A) was developed, which displays a 26.0-fold increase in catalytic activity, 83.5-fold enhancement in half-life (t1/2) at 40 °C (101.4 h), excellent enantioselectivity (>99.9% e.e.), and broad substrate scope. Compared to the wild-type (WT) LbCR, catalytic efficiency (kcat/KM) of LbCRM4 was increased by 28.0 folds. Furthermore, a high concentration of TCAP (400 g/L) can be transformed (99.9% conversion) within 7 h by using LbCRM4 and an isopropanol/alcohol dehydrogenase/NADPH cofactor regeneration system, giving (S)-TCPE in >99.9% e.e., which is the highest recorded space-time yield (STY, 1288.9 g/L/day) to date. Molecular dynamics (MD) simulations and dynamic cross-correlation matrix analysis elucidated the substantial catalytic performance improvement of LbCRM4. Together, the development of LbCRM4 not only overcomes the trade-offs between catalytic activity and thermostability but also affords an efficient biocatalytic approach for the synthesis of (S)-TCPE featuring a record STY, laying a solid foundation for industrial manufacturing of luliconazole and other active pharmaceutical intermediates.

Microbial alcohol dehydrogenases: recent developments and applications in asymmetric synthesis

Alcohol dehydrogenases are a well-known group of enzymes in the class of oxidoreductases that use electron transfer cofactors such as NAD(P)+/NAD(P)H for oxidation or reduction reactions of alcohols or carbonyl compounds respectively. These enzymes are utilized mainly as purified enzymes and offer some advantages in terms of green chemistry. They are environmentally friendly and a sustainable alternative to traditional chemical synthesis of bulk and fine chemicals. Industry has implemented several whole-cell biocatalytic processes to synthesize pharmaceutically active ingredients by exploring the high selectivity of enzymes. Unlike the whole cell system where cofactor regeneration is well conserved within the cellular environment, purified enzymes require additional cofactors or a cofactor recycling system in the reaction, even though cleaner reactions can be carried out with fewer downstream work-up problems. The challenge of producing purified enzymes in large quantities has been solved in large part by the use of recombinant enzymes. Most importantly, recombinant enzymes find applications in many cascade biotransformations to produce several important chiral precursors. Inevitably, several dehydrogenases were engineered as mere recombinant enzymes could not meet the industrial requirements for substrate and stereoselectivity. In recent years, a significant number of engineered alcohol dehydrogenases have been employed in asymmetric synthesis in industry. In a parallel development, several enzymatic and non-enzymatic methods have been established for regenerating expensive cofactors (NAD+/NADP+) to make the overall enzymatic process more efficient and economically viable. In this review article, recent developments and applications of microbial alcohol dehydrogenases are summarized by emphasizing notable examples.

Application of Ketoreductase in Asymmetric Synthesis of Pharmaceuticals and Bioactive Molecules: An Update (2018-2020)

With the rapid development of genomic DNA sequencing, recombinant DNA expression, and protein engineering, biocatalysis has been increasingly and widely adopted in the synthesis of pharmaceuticals, bioactive molecules, fine chemicals, and agrochemicals. In this review, we have summarized the most recent advances achieved (2018-2020) in the research area of ketoreductase (KRED)-catalyzed asymmetric synthesis of chiral secondary alcohol intermediates to pharmaceuticals and bioactive molecules. In the first part, synthesis of chiral alcohols with one stereocenter through the bioreduction of four different ketone classes, namely acyclic aliphatic ketones, benzyl or phenylethyl ketones, cyclic aliphatic ketones, and aryl ketones, is discussed. In the second part, KRED-catalyzed dynamic reductive kinetic resolution and reductive desymmetrization are presented for the synthesis of chiral alcohols with two contiguous stereocenters.

Biocatalysis: Enzymatic Synthesis for Industrial Applications

Biocatalysis has found numerous applications in various fields as an alternative to chemical catalysis. The use of enzymes in organic synthesis, especially to make chiral compounds for pharmaceuticals as well for the flavors and fragrance industry, are the most prominent examples. In addition, biocatalysts are used on a large scale to make specialty and even bulk chemicals. This review intends to give illustrative examples in this field with a special focus on scalable chemical production using enzymes. It also discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.