Identification of an ε-Keto Ester Reductase for the Efficient Synthesis of an (R )-α-Lipoic Acid Precursor

Enantioselective Transformations in the Synthesis of Therapeutic Agents

The proportion of approved chiral drugs and drug candidates under medical studies has surged dramatically over the past two decades. As a consequence, the efficient synthesis of enantiopure pharmaceuticals or their synthetic intermediates poses a profound challenge to medicinal and process chemists. The significant advancement in asymmetric catalysis has provided an effective and reliable solution to this challenge. The successful application of transition metal catalysis, organocatalysis, and biocatalysis to the medicinal and pharmaceutical industries has promoted drug discovery by efficient and precise preparation of enantio-enriched therapeutic agents, and facilitated the industrial production of active pharmaceutical ingredient in an economic and environmentally friendly fashion. The present review summarizes the most recent applications (2008-2022) of asymmetric catalysis in the pharmaceutical industry ranging from process scales to pilot and industrial levels. It also showcases the latest achievements and trends in the asymmetric synthesis of therapeutic agents with state of the art technologies of asymmetric catalysis.

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.

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

In this work, we have identified a significantly improved variant (S131Y/Q252I) of the natural ϵ-keto ester reductase CpAR2 from Candida parapsilosis for efficiently manufacturing (R)-8-chloro-6-hydroxyoctanoic acid [(R)-ECHO] through co-evolution of activity and thermostability. The activity of the variant CpAR2_S131Y/Q252I towards the ϵ-keto ester ethyl 8-chloro-6-oxooctanoate was improved to 214 U mg^-1 -from 120 U mg^-1 in the case of the wild-type enzyme (CpAR2_WT )-and the half-deactivating temperature (T₅₀ , for 15 min incubation) was simultaneously increased by 2.3 °C in relation to that of CpAR2_WT . Consequently, only 2 g L^-1 of lyophilized E. coli cells harboring CpAR2_S131Y/Q252I and a glucose dehydrogenase (GDH) were required in order to achieve productivity similar to that obtained in our previous work, under optimized reaction conditions (530 g L^-1  d^-1 ). This result demonstrated a more economical and efficient process for the production of the key (R)-α-lipoic acid intermediate ethyl 8-chloro-6-oxooctanoate.

Preparation of Chitosan Molecularly Imprinted Polymers and the Recognition Mechanism for Adsorption of Alpha-Lipoic Acid

Two effective molecularly imprinted polymers for the adsorption of alpha-lipoic acid (ALA) were synthesized by the cross-linking of chitosan with epichlorohydrin (ECH) and glutaraldehyde (GLU), respectively, in the presence of ALA as template molecules. Investigations on the molar ratios of ALA and chitosan (–NH₂) in the preparation of chitosan molecularly imprinted polymers (MIPs) were carried out with a factor of ALA rebinding capabilities. The surface morphology and chemical properties of the polymers were characterized. The optimized MIPs crosslinked by ECH (MIPs–ECH) and MIPs crosslinked by GLU (MIPs–GLU) had adsorption capabilities of 12.09 mg/g and 19.72 mg/g for ALA, respectively. The adsorption behaviors of two kinds of chitosan MIPs including adsorption kinetics and isotherms were investigated in detail. Adsorption and kinetic binding experiments showed that the prepared MIPs–ECH and MIPs–GLU had selective adsorption and excellent affinity for ALA. In addition, the possible binding models between ALA and chitosan oligosaccharide were predicted by molecular dynamics simulation.

Characterization of a Carbonyl Reductase from Rhodococcus erythropolis WZ010 and Its Variant Y54F for Asymmetric Synthesis of (S)-N-Boc-3-Hydroxypiperidine

The recombinant carbonyl reductase from Rhodococcus erythropolis WZ010 (ReCR) demonstrated strict (S)-stereoselectivity and catalyzed the irreversible reduction of N-Boc-3-piperidone (NBPO) to (S)-N-Boc-3-hydroxypiperidine [(S)-NBHP], a key chiral intermediate in the synthesis of ibrutinib. The NAD(H)-specific enzyme was active within broad ranges of pH and temperature and had remarkable activity in the presence of higher concentration of organic solvents. The amino acid residue at position 54 was critical for the activity and the substitution of Tyr54 to Phe significantly enhanced the catalytic efficiency of ReCR. The k_cat/K_m values of ReCR Y54F for NBPO, (R/S)-2-octanol, and 2-propanol were 49.17 s⁻¹ mM⁻¹, 56.56 s⁻¹ mM⁻¹, and 20.69 s⁻¹ mM⁻¹, respectively. In addition, the (S)-NBHP yield was as high as 95.92% when whole cells of E. coli overexpressing ReCR variant Y54F catalyzed the asymmetric reduction of 1.5 M NBPO for 12 h in the aqueous/(R/S)-2-octanol biphasic system, demonstrating the great potential of ReCR variant Y54F for practical applications.

Asymmetric bioreduction of β-ketoesters derivatives by Kluyveromyces marxianus: influence of molecular structure on the conversion and enantiomeric excess

This study presents the bioreduction of six β-ketoesters by whole cells of Kluyveromyces marxianus and molecular investigation of a series of 13 β-ketoesters by hologram quantitative structure-activity relationship (HQSAR) in order to relate with conversion and enantiomeric excess of β-stereogenic-hydroxyesters obtained by the same methodology. Four of these were obtained as (R)-configuration and two (S)-configuration, among them four compounds exhibited >99% enantiomeric excess. The β-ketoesters series LUMO maps showed that the β-carbon of the ketoester scaffold are exposed to undergo nucleophilic attack, suggesting a more favorable β-carbon side to enzymatic reduction based on adopted molecular conformation at the reaction moment. The HQSAR method was performed on the β-ketoesters derivatives separating them into those provided predominantly (R)- or (S)-β-hydroxyesters. The HQSAR models for both (R)- and (S)-configuration showed high predictive capacity. The HQSAR contribution maps suggest the importance of β-ketoesters scaffold as well as the substituents attached therein to asymmetric reduction, showing a possible influence of the ester group carbonyl position on the molecular conformation in the enzyme catalytic site, exposing a β-carbon side to the bioconversion to (S)- and (R)-enantiomers.

A green-by-design system for efficient bio-oxidation of an unnatural hexapyranose into chiral lactone for building statin side-chains

An improved dehydrogenase LeADH_{I87F/N235H/P236H} was co-expressed with a NADPH oxidase in E. coli for bio-oxidation of a key statin side-chain precursor.

Microwave-Assisted Resolution of α-Lipoic Acid Catalyzed by an Ionic Liquid Co-Lyophilized Lipase

The combination of the ionic liquid co-lyophilized lipase and microwave irradiation was used to improve enzyme performance in enantioselective esterification of α-lipoic acid. Effects of various reaction conditions on enzyme activity and enantioselectivity were investigated. Under optimal condition, the highest enantioselectivity (E = 41.2) was observed with a high enzyme activity (178.1 μmol/h/mg) when using the ionic liquid co-lyophilized lipase with microwave assistance. Furthermore, the ionic liquid co-lyophilized lipase exhibited excellent reusability under low power microwave.