An enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid via asymmetric hydrogenation

Microbial Lipases and Their Potential in the Production of Pharmaceutical Building Blocks

Processes involving lipases in obtaining active pharmaceutical ingredients (APIs) are crucial to increase the sustainability of the industry. Despite their lower production cost, microbial lipases are striking for their versatile catalyzing reactions beyond their physiological role. In the context of taking advantage of microbial lipases in reactions for the synthesis of API building blocks, this review focuses on: (i) the structural origins of the catalytic properties of microbial lipases, including the results of techniques such as single particle monitoring (SPT) and the description of its selectivity beyond the Kazlauskas rule as the "Mirror-Image Packing" or the "Key Region(s) rule influencing enantioselectivity" (KRIE); (ii) immobilization methods given the conferred operative advantages in industrial applications and their modulating capacity of lipase properties; and (iii) a comprehensive description of microbial lipases use as a conventional or promiscuous catalyst in key reactions in the organic synthesis (Knoevenagel condensation, Morita-Baylis-Hillman (MBH) reactions, Markovnikov additions, Baeyer-Villiger oxidation, racemization, among others). Finally, this review will also focus on a research perspective necessary to increase microbial lipases application development towards a greener industry.

Asymmetric Organocatalysis—A Powerful Technology Platform for Academia and Industry: Pregabalin as a Case Study

Enantioselective organocatalysis has quickly established itself as the third pillar of asymmetric catalysis. It is a powerful technology platform, and it has a tremendous impact in both academic and industrial settings. By focusing on pregabalin, as a case study, this Perspective aims to show how a process amenable to industry of a simple chiral molecule can be tackled in several different ways using organocatalysis.

Engineering of reaction specificity, enantioselectivity and catalytic activity of nitrilase for highly efficient synthesis of pregabalin precursor

Simultaneous evolution of multiple enzyme properties remains challenging in protein engineering. A chimeric nitrilase (BaNIT_M0 ) with high activity towards isobutylsuccinonitrile (IBSN) was previously constructed for biosynthesis of pregabalin precursor (S)-3-cyano-5-methylhexanoic acid ((S)-CMHA). However, BaNIT_M0 also catalyzed the hydration of IBSN to produce by-product (S)-3-cyano-5-methylhexanoic amide. In order to obtain industrial nitrilase with vintage performance, we carried out engineering of BaNIT_M0 for simultaneous evolution of reaction specificity, enantioselectivity and catalytic activity. The best variant V82L/M127I/C237S (BaNIT_M2 ) displayed higher enantioselectivity (E=515), increased enzyme activity (5.4-fold) and reduced amide formation (from 15.8% to 1.9 %) compared with BaNIT_M0 . Structure analysis and molecular dynamics simulations indicated that mutation M127I and C237S restricted the movement of E66 in the catalytic triad, resulting in decreased amide formation. Mutation V82L was incorporated to induce the reconstruction of the substrate binding region in the enzyme catalytic pocket, engendering the improvement of stereoselectivity. Enantio- and regio-selective hydrolysis of 150 g/L IBSN using 1.5 g/L E. coli cells harboring BaNIT_M2 as biocatalyst afforded (S)-CMHA with >99.0% ee and 45.9% conversion, which highlighted the robustness of BaNIT_M2 for efficient manufacturing of pregabalin. This article is protected by copyright. All rights reserved.

Reducing Challenges in Organic Synthesis with Stereoselective Hydrogenation and Tandem Catalysis

Tandem catalysis enables the rapid construction of complex architectures from simple building blocks. This Perspective shares our interest in combining stereoselective hydrogenation with transformations such as isomerization, oxidation, and epimerization to solve diverse challenges. We highlight the use of tandem hydrogenation for preparing complex natural products from simple prochiral building blocks and present tandem catalysis involving transfer hydrogenation and dynamic kinetic resolution. Finally, we underline recent breakthroughs and opportunities for asymmetric hydrogenation.

Tailor-made amino acids in the design of small-molecule blockbuster drugs

The role of amino acids (AAs) in modern health industry is well-appreciated. Residues of individual AAs, or their chemical modifications, such as diamines and amino alcohols, are frequently found in the structures of modern pharmaceuticals. The goal of this review article, is to emphasize that, currently, tailor-made AAs serve as key structural features in many most successful pharmaceuticals, so-called blockbuster drugs. In the present article, we profile 14 small-molecule drugs, underscoring the breadth of structural variety of AAs applications in numerous therapeutic areas. For each compound, we provide spectrum of biological activity, medicinal chemistry discovery, and synthetic approaches.

Enantioconvergent and enantiodivergent catalytic hydrogenation of isomeric olefins

The asymmetric catalytic hydrogenation of olefins is one of the most widely studied and utilised transformations in asymmetric synthesis. This straightforward and atom-economical strategy can provide excellent enantioselectivity for a broad variety of substrates and is widely relevant for both industrial applications and academic research. In many instances the hydrogenation is stereospecific in the regard that the E-Z-geometry of the olefin governs the stereochemistry of the hydrogenation, producing an enantiodivergent outcome. Interestingly, the possibility to hydrogenate E- and Z-isomer mixtures to a single stereoisomer in an enantioconvergent manner has been reported. This avoids the need for synthesis of geometrically pure alkene starting materials and therefore constitutes a significant practical advantage. This review article aims to provide an overview of the different stereochemical outcomes in the hydrogenation of olefins. Although the field is well developed and selectivity models have been proposed for a number of catalytic systems, an organized collection of enantioconvergent results, as opposed to the more common enantiodivergent case, might promote new investigation into these phenomena.

Access to chiral cyano-containing five-membered rings through enantioconvergent rhodium-catalyzed cascade cyclization of a diastereoisomeric E/Z mixture of 1,6-enynes

In contrast to the intermolecular rhodium-catalyzed asymmetric 1,4-addition of organometallic reagents to activated alkenes, the asymmetric arylative cyclization of a diastereoisomeric E/Z mixture of 1,6-enynes afforded only one major enantiomer.

Chiral Sulfinyl-Based Olefin Ligands for Rhodium-Catalysed Asymmetric Conjugate Addition of Arylboronic Acids to Cyanoalkenes

A rhodium/sulfinyl-based olefin ligand-catalysed asymmetric conjugate addition of arylboronic acids to cyanoalkenes without activation groups has been developed, where p-tolylsulfinyl-functionalised olefin ligands have been shown to be effective and with moderate enantioselectivities. This is the first example of applying chiral sulfinyl-based olefin ligands in the catalytic asymmetric addition to cyanoalkenes.

Biocatalysis for synthesis of pharmaceuticals

Chirality is a key factor in the safety and efficacy of many drug products and thus the production of single enantiomers of drug intermediates and drugs has become important and state of the art in the pharmaceutical industry. There has been an increasing awareness of the enormous potential of microorganisms and enzymes (biocatalysts) for the transformation of synthetic chemicals with high chemo-, regio- and enatioselectivities providing products in high yields and purity. In this article, biocatalytic processes are described for the synthesis of key chiral intermediates for development pharmaceuticals.

Asymmetric Hydrogenation of β-Aryloxy/Alkoxy Cinnamic Nitriles and Esters

A highly efficient and enantioselective hydrogenation of β-aryloxy/alkoxy cinnamic nitriles and esters under mild conditions has been realized by using a rhodium catalyst with a chiral f-spiroPhos ligand. The method provides efficient access to the asymmetric synthesis of a variety of chiral β-oxy-functionalized nitriles and esters with excellent enantioselectivities (up to 99.9% ee) and high turnover numbers (TON of up to 50000). This methodology has also been successfully applied to the concise and practical synthesis of the chiral pharmaceutical nisoxetine.

Solvents and sustainable chemistry

Solvents are widely recognized to be of great environmental concern. The reduction of their use is one of the most important aims of green chemistry. In addition to this, the appropriate selection of solvent for a process can greatly improve the sustainability of a chemical production process. There has also been extensive research into the application of so-called green solvents, such as ionic liquids and supercritical fluids. However, most examples of solvent technologies that give improved sustainability come from the application of well-established solvents. It is also apparent that the successful implementation of environmentally sustainable processes must be accompanied by improvements in commercial performance.

Exploiting Enzymatic Dynamic Reductive Kinetic Resolution (DYRKR) in Stereocontrolled Synthesis

Over the past two decades, the domains of both frontline synthetic organic chemistry and process chemistry and have seen an increase in crosstalk between asymmetric organic/organometallic approaches and enzymatic approaches to stereocontrolled synthesis. This review highlights the particularly auspicious role for dehydrogenase enzymes in this endeavor, with a focus on dynamic reductive kinetic resolutions (DYRKR) to "deracemize" building blocks, often setting two stereocenters in so doing. The scope and limitations of such dehydrogenase-mediated processes are overviewed, as are future possibilities for the evolution of enzymatic DYRKR.

Green chemistry approaches as sustainable alternatives to conventional strategies in the pharmaceutical industry

Green chemistry is a rapidly developing field for the sustainable development of future science and technology. Incorporating green chemistry into the synthesis of active pharmaceutical ingredients and intermediates is of ongoing importance to the pharmaceutical industry.

Diasteroselective conjugate addition of diethylaluminum cyanide to a conjugated N-enoyl system: an alternative synthesis of (S)-pregabalin

We have explored in this work the conjugate addition of diethylaluminum cyanide (Nagata’s reagent) to an N-enoyl system bearing the (R)-4-phenyl-2-oxazolidinone chiral auxiliary. Since this method provided a practical synthesis of γ-amino acids, we report the conjugate addition of diethylaluminum cyanide as the key step in the synthesis of (S)-pregabalin 1 in a five-step sequence of reactions from commercially available starting materials.

Synthesis of optically active β- or γ-alkyl-substituted alcohols through copper-catalyzed asymmetric allylic alkylation with organolithium reagents

An efficient one-pot synthesis of optically active β-alkyl-substituted alcohols through a tandem copper-catalyzed asymmetric allylic alkylation (AAA) with organolithium reagents and reductive ozonolysis is presented. Furthermore, hydroboration-oxidation following the Cu-catalyzed AAA leads to the corresponding homochiral γ-alkyl-substituted alcohols.

Rhodium-catalysed asymmetric hydrogenation as a valuable synthetic tool for the preparation of chiral drugs

During the last few decades, rhodium-catalysed asymmetric hydrogenation of diverse alkene classes has emerged as a powerful synthetic tool in the pharmaceutical industry, contributing to the manufacturing of chiral drugs, recent drug candidates for clinical trials, and major synthetic precursors of drugs. Numerous efficient chiral rhodium complexes, most of which are derived from enantiopure phosphorus ligands, have been employed for the preparation of chiral drugs and intermediates thereof. This review article is intended to provide an updated overview of the most striking contributions in this field, organised according to substrate class: acrylate derivatives, itaconate derivatives, α-substituted enamides, α-arylenol acetates, and minimally functionalised olefins.

Improved production of Pseudomonas sp. ECU1011 acetyl esterase by medium design and fed-batch fermentation

We optimized culture medium and batch-fed fermentation conditions to enhance production of an acetyl esterase from Pseudomonas sp. ECU1011 (PSAE). This enzyme enantioselectively deacetylates α-acetoxyphenylacetic acid. The medium was redesigned by single-factor and statistical optimization. The addition of ZnSO(4) enhanced enzyme production by 37%. Yeast extract concentration was directly associated with the enzyme production. The fermentation was scaled up in a 5-l fermenter with the optimized medium, and the correlations between enzyme production and dissolved oxygen, pH, and feeding strategy were investigated. The fermentation process was highly oxygen-demanding, pH sensitive and mandelic acid-inducible. The fermentation pH was controlled at 7.5 by a pH and dissolved oxygen feedback strategy. Feeding mandelic acid as both a pH regulator and an enzyme inducer increased the enzyme production by 23%. The results of the medium redesign experiments were confirmed and explained in fed-batch culture experiments. Mathematical models describing the fermentation processes indicated that the enzyme production was strongly associated with cell growth. The optimized pH and dissolved oxygen stat fed-batch process resulted high volumetric production of PSAE (4166 U/l, 7.2-fold higher than the initial) without enantioselectivity decline. This process has potential applications for industrial production of chiral mandelic acid or its derivatives.

Efficient, enantioselective assembly of silanediol protease inhibitors

A five-step assembly of silicon-protected dipeptide mimics from commercially available reagents is described. This methodology makes silanediol protease inhibitors readily available for the first time. The sequence features asymmetric hydrosilylation, a novel reduction of a silyl ether to a silyllithium reagent, and addition of this dianion to a sulfinimine, to produce the complete inhibitor skeleton with full control of stereochemistry. Oxidation of the primary alcohol to an acid completes the synthesis.