Tandem Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis

Enzyme-Immobilized Porous Crystals for Environmental Applications

Developing efficient technologies to eliminate or degrade contaminants is paramount for environmental protection. Biocatalytic decontamination offers distinct advantages in terms of selectivity and efficiency; however, it still remains challenging when applied in complex environmental matrices. The main challenge originates from the instability and difficult-to-separate attributes of fragile enzymes, which also results in issues of compromised activity, poor reusability, low cost-effectiveness, etc. One viable solution to harness biocatalysis in complex environments is known as enzyme immobilization, where a flexible enzyme is tightly fixed in a solid carrier. In the case where a reticular crystal is utilized as the support, it is feasible to engineer next-generation biohybrid catalysts functional in complicated environmental media. This can be interpreted by three aspects: (1) the highly crystalline skeleton can shield the immobilized enzyme against external stressors. (2) The porous network ensures the high accessibility of the interior enzyme for catalytic decontamination. And (3) the adjustable and unambiguous structure of the reticular framework favors in-depth understanding of the interfacial interaction between the framework and enzyme, which can in turn guide us in designing highly active biocomposites. This Review aims to introduce this emerging biocatalysis technology for environmental decontamination involving pollutant degradation and greenhouse gas (carbon dioxide) conversion, with emphasis on the enzyme immobilization protocols and diverse catalysis principles including single enzyme catalysis, catalysis involving enzyme cascades, and photoenzyme-coupled catalysis. Additionally, the remaining challenges and forward-looking directions in this field are discussed. We believe that this Review may offer a useful biocatalytic technology to contribute to environmental decontamination in a green and sustainable manner and will inspire more researchers at the intersection of the environment science, biochemistry, and materials science communities to co-solve environmental problems.

Interfacing Whole Cell Biocatalysis with a Biocompatible Pictet-Spengler Reaction for One-Pot Syntheses of Tetrahydroisoquinolines and Tryptolines

Biocatalytic processes are highly selective and specific. However, their utility is limited by the comparatively narrow scope of enzyme-catalysed transformations. To expand product scope, we are developing biocompatible processes that combine biocatalytic reactions with chemo-catalysis in single-flask processes. Here, we show that a chemocatalysed Pictet-Spengler annulation can be interfaced with biocatalysed alcohol oxidation. This two-step, one-pot cascade reaction converts tyramine and aliphatic alcohols to tetrahydroisoquinoline alkaloids in aqueous buffer at mild pH. Tryptamine derivatives are also efficiently converted to tryptolines. Optimization of stoichiometry, pH, reaction time, and whole-cell catalyst deliver the tetrahydroisouinolines and tryptolines in >90 % and >40 % isolated yield, respectively, with excellent regioselectivity.

Introducing Savie: A Biodegradable Surfactant Enabling Chemo- and Biocatalysis and Related Reactions in Recyclable Water

Savie is a biodegradable surfactant derived from vitamin E and polysarcosine (PSar) developed for use in organic synthesis in recyclable water. This includes homogeneous catalysis (including examples employing only ppm levels of catalyst), heterogeneous catalysis, and biocatalytic transformations, including a multistep chemoenzymatic sequence. Use of Savie frequently leads to significantly higher yields than do conventional surfactants, while obviating the need for waste-generating organic solvents.

Effective Production of Selected Dioxolanes by Sequential Bio- and Chemocatalysis Enabled by Adapted Solvent Switching

Most combinations of chemo- and biocatalysis take place in aqueous media or require a solvent change with complex intermediate processing. Using enzymes in the same organic solvent as the chemocatalyst eliminates this need. Here, it was shown that a complete chemoenzymatic cascade to form dioxolanes could be carried out in a purely organic environment. The result, including downstream processing, was compared with a classical mode, shifting solvent. First, a two-step enzyme cascade starting from aliphatic aldehydes to chiral diols (3,4-hexanediol and 4,5-octanediol) was run either in an aqueous buffer or in the potentially biobased solvent cyclopentyl methyl ether. Subsequently, a ruthenium molecular catalyst enabled the conversion to dioxolanes [e. g., (4S,5S)-dipropyl-1,3-dioxolane]. Importantly, the total synthesis of this product was not only highly stereoselective but also based on the combination of biomass, CO₂ , and hydrogen, thus providing an important example of a bio-hybrid chemical.

Expanding the Synthetic Toolbox through Metal-Enzyme Cascade Reactions

The combination of metal-, photo-, enzyme-, and/or organocatalysis provides multiple synthetic solutions, especially when the creation of chiral centers is involved. Historically, enzymes and transition metal species have been exploited simultaneously through dynamic kinetic resolutions of racemates. However, more recently, linear cascades have appeared as elegant solutions for the preparation of valuable organic molecules combining multiple bioprocesses and metal-catalyzed transformations. Many advantages are derived from this symbiosis, although there are still bottlenecks to be addressed including the successful coexistence of both catalyst types, the need for compatible reaction media and mild conditions, or the minimization of cross-reactivities. Therefore, solutions are here also provided by means of catalyst coimmobilization, compartmentalization strategies, flow chemistry, etc. A comprehensive review is presented focusing on the period 2015 to early 2022, which has been divided into two main sections that comprise first the use of metals and enzymes as independent catalysts but working in an orchestral or sequential manner, and later their application as bionanohybrid materials through their coimmobilization in adequate supports. Each part has been classified into different subheadings, the first part based on the reaction catalyzed by the metal catalyst, while the development of nonasymmetric or stereoselective processes was considered for the bionanohybrid section.

Green Synthesis of Spirooxindoles via Lipase-Catalyzed One-Pot Tandem Reaction in Aqueous Media

The development of non-natural enzymatic catalysis is important for multicomponent tandem organic transformations. However, the delicate acting environments of biological enzymes still present some challenges in the synthesis of spirooxindole skeleton via enzymatic catalysis. To address these issues, a lipase-catalyzed method was developed for the synthesis of spirooxindole frameworks. Using easily available isatins, cycloketones, and malononitriles as substrates, mild reaction conditions, and a reasonable reaction time, moderate to good yields (67–92%) and excellent functional group tolerance were accomplished via this protocol. The related mechanism explanation is also speculated in this paper.

Where Chemocatalysis Meets Biocatalysis: In Water

Chemoenzymatic catalysis, by definition, involves the merging of sequential reactions using both chemocatalysis and biocatalysis, typically in a single reaction vessel. A major challenge, the solution to which, however, is associated with numerous advantages, is to run such one-pot processes in water: the majority of enzyme-catalyzed processes take place in water as Nature's reaction medium, thus enabling a broad synthetic diversity when using water due to the option to use virtually all types of enzymes. Furthermore, water is cheap, abundantly available, and environmentally friendly, thus making it, in principle, an ideal reaction medium. On the other hand, most chemocatalysis is routinely performed today in organic solvents (which might deactivate enzymes), thus appearing to make it difficult to combine such reactions with biocatalysis toward one-pot cascades in water. Several creative approaches and solutions that enable such combinations of chemo- and biocatalysis in water to be realized and applied to synthetic problems are presented herein, reflecting the state-of-the-art in this blossoming field. Coverage has been sectioned into three parts, after introductory remarks: (1) Chapter 2 focuses on historical developments that initiated this area of research; (2) Chapter 3 describes key developments post-initial discoveries that have advanced this field; and (3) Chapter 4 highlights the latest achievements that provide attractive solutions to the main question of compatibility between biocatalysis (used predominantly in aqueous media) and chemocatalysis (that remains predominantly performed in organic solvents), both Chapters covering mainly literature from ca. 2018 to the present. Chapters 5 and 6 provide a brief overview as to where the field stands, the challenges that lie ahead, and ultimately, the prognosis looking toward the future of chemoenzymatic catalysis in organic synthesis.

Chemo-Biocascade Reactions Enabled by Metal–Organic Framework Micro-Nanoreactor

The one-pot combination of biocatalytic and chemocatalytic reactions represents an economically and ecologically attractive concept in the emerging cascade processes for manufacturing. The mutual incompatibility of biocatalysis and chemocatalysis, however, usually causes the deactivation of catalysts, the mismatching of reaction dynamic, and further challenges their integration into concurrent chemo-biocascades. Herein, we have developed a convenient strategy to construct versatile functional metal–organic framework micro-nanoreactors (MOF–MNRs), which can realize not only the encapsulation and protection of biocatalysts but also the controllable transmission of substances and the mutual communication of the incompatible chemo-biosystems. Importantly, the MOFs serving as the shell of MNRs have the capability of enriching the chemocatalysts on the surface and improving the activity of the chemocatalysts to sufficiently match the optimum aqueous reaction system of biocatalysts, which greatly increase the efficiency in the combined concurrent chemo-biocatalysis. Such strategy of constructing MOF–MNRs provides a unique platform for connecting the “two worlds” of chemocatalysis and biocatalysis.

Recent Advances in Biocatalysis for Drug Synthesis

Biocatalysis is constantly providing novel options for the synthesis of active pharmaceutical ingredients (APIs). In addition to drug development and manufacturing, biocatalysis also plays a role in drug discovery and can support many active ingredient syntheses at an early stage to build up entire scaffolds in a targeted and preparative manner. Recent progress in recruiting new enzymes by genome mining and screening or adapting their substrate, as well as product scope, by protein engineering has made biocatalysts a competitive tool applied in academic and industrial spheres. This is especially true for the advances in the field of nonribosomal peptide synthesis and enzyme cascades that are expanding the capabilities for the discovery and synthesis of new bioactive compounds via biotransformation. Here we highlight some of the most recent developments to add to the portfolio of biocatalysis with special relevance for the synthesis and late-stage functionalization of APIs, in order to bypass pure chemical processes.

Chiral aldehyde induced tandem conjugated addition-lactamization reaction for constructing full-substituted pyroglutamic acids

A catalytic asymmetric tandem reaction including a chiral aldehyde catalyzed conjugated addition and an intramolecular lactamization is reported in this work. Under the optimal reaction conditions, various full-substituted pyroglutamic acids...

Polymer-templated supramolecular co-assemblies of proteins and metal oxide clusters as versatile platform for chemo-enzymatic catalysis

The hybridization of enzymes and inorganics in controlled manner is challenging, however, critical for the development of chemo-enzymatic cascade catalyst with high efficiency and selectivity. Here, proteins and metal oxide clusters can be facilely co-assembled on the surface of colloid of poly(4-vinylpyridine) (P4VP) via hydrogen bonding, due to their enriched surface hydrogen bonding donors. The co-assembly method can be generally applied for preparing chemo-enzymatic catalyst within the selected database of various proteins and metal oxide clusters while the assembly units retain their structures and activities. Typically, a 2.5 nm metal oxide cluster {Mo₇₂Fe₃₀}, with peroxidase-like activity, are complexed with glucose oxidase (GOX) on P4VP for the catalysis against the oxidization of o-dianisidine (ODA) with the existence of glucose. Due to the synergistic effects of chemical and enzymatic catalysis, the co-assemblies show even higher ODA oxidation activity compared to GOX/catalase bi-enzymatic system, confirming the effectiveness of the co-assembly protocol for cascade catalysis and enabling its applications in rapid glucose detection and biomass conversion.

Organocatalytic Cascade Reaction of Aliphatic Enals and Benzoylnitromethane: Synthesis of Enantioenriched Tetrasubstituted Cyclohexene Carbaldehyde

A new example of the reactivity of enals with benzoylnitromethane was studied in a Michael-Michael-Aldol-Dehydration quadruple organocascade reaction. The reaction unexpectedly yielded a tetrasubstituted cyclohexene carbaldehyde with excellent enantiomeric excess when crotonaldehyde was used as the Michael-acceptor, whereas using (E)-Hex-2-enal as the Michael-acceptor formed a cyclic hemiacetal by steering the reaction into the intramolecular formation of the same intermediate via a Michael-Heterocyclization domino reaction.

A comparative study on flavour components and therapeutic properties of unfermented and fermented defatted soybean meal extract

Microbial fermentation of plant material alters the composition of volatile and non-volatile plant natural products. We investigated the antioxidant, anticancer, and antiviral properties of extracts of defatted soybean meal fermented with Aspergillus fumigatus F-993 or A. awamori FB-133 using in vitro methods. Gas chromatography-mass spectrometry analysis of soybean meal fermented with A. awamori FB-133 and A. fumigatus F-993 identified 26 compounds with 11,14-octadecadienoic acid and methyl ester (63.63%) and 31 compounds with butylated hydroxytoluene (66.83%) and δ-myrcene (11.43%) as main constituents, respectively. The antioxidant activities of DSM extract were 3.362 ± 0.05 and 2.11 ± 0.02 mmol TE/mL, FDSM treated with A. awamori FB-133 were 4.763 ± 0.05 and 3.795 ± 0.03 mmol TE/mL and FDSM treated with A. fumigatus F-993 were 4.331 ± 0.04 and 3.971 ± 0.02 mmol TE/mL as determined by ABTS and FRAP assays, respectively. Both fermented extracts had better antioxidant activity than the unfermented extract as shown by multiple antioxidant activity assays. The concentration of fermented extracts required for 50% inhibition of cell viability was significantly lower than that of the unfermented extract when tested against the human liver cancer cell line HepG2 as shown by cell viability assays, indicating strong anticancer activity. The IC50 values for DSM, FDSM with A. fumigatusF-993 and FDSM with A. awamori FB-133 were27, 16.88 and 8.60 μg/mL, respectively. The extract of FDSM with A. awamori FB-133 showed the strongest anticancer activity, compared to DSM and FDSM with A. FumigatusF-993 extracts. Fermented extracts also reduced hepatitis A virus titres to a greater extent than unfermented extracts, thus showing strong antiviral property. Hepatitis A virus titres were reduced by 2.66 and 3 log10/0.1 mL by FDSM with A. fumigatusF-993 and FDSM by A.awamori FB-133, respectively, compared to DSM (5.50 log10/0.1 mL). Thus, the fermentation of soybean meal with A. fumigatusF-993 or A. awamori FB-133 improves the therapeutic effect of soybean extracts, which can be used in traditional medicine.

Integrating biocatalysis with chemocatalysis for selective transformations

The integration of biocatalysis with chemocatalysis combines the excellent selectivity of the former with the robust reactivity of the latter and offers many advantages, such as lower cost, higher yield, enhanced selectivity, as well as less waste generation. In spite of the challenge of incompatibilities between different classes of catalysts, recent advances in synthetic chemistry and biology provide ample opportunities for multistep cascade transformations that combine biocatalysis and chemocatalysis. Herein, we review recent progress in merging biocatalysis with chemocatalysis, highlighting selected examples of photo-/electricity-driven biotransformations and recently developed strategies for addressing the catalyst incompatibility issue.

The various levels of integration of chemo- and bio-catalysis towards hybrid catalysis

Hybrid catalysis is an emerging concept that combines chemo- and biocatalysts in a wide variety of approaches. Combining the specifications and advantages of multiple disciplines, it is a very promising way to diversify tomorrow's catalysis.

Developing Multicompartment Biopolymer Hydrogel Beads for Tandem Chemoenzymatic One-Pot Process

Chemoenzymatic processes have been gaining interest to implement sustainable reaction steps or even create new synthetic routes. In this study, we combined Grubbs’ second-generation catalyst with pig liver esterase and conducted a chemoenzymatic one-pot process in a tandem mode. To address sustainability, we encapsulated the catalysts in biopolymer hydrogel beads and conducted the reaction cascade in an aqueous medium. Unfortunately, conducting the process in tandem led to increased side product formation. We then created core-shell beads with catalysts located in different compartments, which notably enhanced the selectivity towards the desired product compared to homogeneously distributing both catalysts within the matrix. Finally, we designed a specific large-sized bead with a diameter of 13.5 mm to increase the diffusion route of the Grubbs’ catalyst-containing shell. This design forced the ring-closing metathesis to occur first before the substrate could diffuse into the pig liver esterase-containing core, thus enhancing the selectivity to 75%. This study contributes to addressing reaction-related issues by designing specific immobilisates for chemoenzymatic processes.

Asymmetric and Selective Biocatalysis

The synthesis of compounds or chiral building-blocks with the desired configuration is one of the greatest challenges of chemistry and is of great interest in different fields such as analytical chemistry and especially in fine and pharmaceutical chemistry. [...]

Expanding the boundary of biocatalysis: design and optimization of in vitro tandem catalytic reactions for biochemical production

Biocatalysts have been increasingly used in the synthesis of fine chemicals and medicinal compounds due to significant advances in enzyme discovery and engineering. To mimic the synergistic effects of cascade reactions catalyzed by multiple enzymes in nature, researchers have been developing artificial tandem enzymatic reactions in vivo by harnessing synthetic biology and metabolic engineering tools. There is also growing interest in the development of one-pot tandem enzymatic or chemo-enzymatic processes in vitro due to their neat and concise catalytic systems and product purification procedures. In this review, we will briefly summarize the strategies of designing and optimizing in vitro tandem catalytic reactions, highlight a few representative examples, and discuss the future trend in this field.

Tandem Biocatalysis Unlocks the Challenging de Novo Production of Plant Natural Products

Intimate partnership: Knowledge of the biocatalytic cascades in different cellular compartments is limited, but deciphering these systems in nature can be used to inspire synthetic strategies. Two studies report new insights into the biosynthesis of alkaloids and sesterterpenoids in plants. This highlight presents these novel biotransformations to illustrate how tandem biocatalysis can impact the future of natural product production.

Overcoming the Incompatibility Challenge in Chemoenzymatic and Multi-Catalytic Cascade Reactions

Multi-catalytic cascade reactions bear a great potential to minimize downstream and purification steps, leading to a drastic reduction of the produced waste. In many examples, the compatibility of chemo- and biocatalytic steps could be easily achieved. Problems associated with the incompatibility of the catalysts and their reactions, however, are very frequent. Cascade-like reactions can hardly occur in this way. One possible solution to combine, in principle, incompatible chemo- and biocatalytic reactions is the defined control of the microenvironment by compartmentalization or scaffolding. Current methods for the control of the microenvironment of biocatalysts go far beyond classical enzyme immobilization and are thus believed to be very promising tools to overcome incompatibility issues and to facilitate the synthetic application of cascade reactions. In this Minireview, we will summarize recent synthetic examples of (chemo)enzymatic cascade reactions and outline promising methods for their spatial control either by using bio-derived or synthetic systems.