R.B. Leveson-Gower

During efforts to explore the range of reactions catalyzed by the previously-engineered B12-dependent enzyme CarH*, we found that this enzyme catalyzes N-alkylation of aniline using ethyl diazoacetate but that B12 itself provides only trace conversion for this reaction. This observation suggested that the unique primary and second coordination sphere provided by CarH* accelerates non-native N-alkylation catalysis and that other B12-dependent proteins could provide further improvements in activity. We used a structural homology search to identify the corrinoid protein MtaC, which was reconstituted with B12 to generate a catalyst with significantly-improved aniline N-alkylation activity on a range of substrates. MtaC also displays remarkable thermal stability and organic solvent tolerance, remaining folded even in pure methanol. These results highlight how protein scaffolds can be used to impart new activity and other beneficial properties to metal catalysts and suggest that MtaC could serve as a useful platform for non-native B12 catalysis.

A route involving both enzymatic and spontaneous chemical reactions was designed for the synthesis of L-homophenylalanine from inexpensive building blocks. One enzyme in the cascade, EcQOR, was identified as the first ene reductase to catalyze the reduction of an unsaturated aromatic keto acid. This study shows the potential of introducing spontaneous chemical reactions into enzymatic cascades for the synthesis of valuable chemicals.

Abstract

L-Homophenylalanine (L-HPA) is a vital building block for the synthesis of numerous chiral drugs. However, the high cost of starting materials limits the industrial production of L-HPA. In this study, an enzymatic-spontaneous chemical cascade route for L-HPA production was designed based on retrosynthetic analysis. This route, using simple benzaldehyde and pyruvate as starting materials, is extremely cost-effective. The enzymes were screened and further assembled in E. coli, and TipheDH was identified as the rate-limiting enzyme. Therefore, TipheDH was engineered to improve its specific activity (by 82 %) and expression level (by 254 %), thus generating the best strain (W14). W14 exhibited the optimum enzyme activity ratio (1.7 : 1.1 : 1 : 1.8) and demonstrated production of 100.9 g L⁻¹ of L-HPA (with 94 % conversion, >99 % ee) in a 5-L reactor. This route effectively exploits the power of cascades and offers insight into avenues for synthesizing other valuable chemicals from inexpensive building blocks.

Nature Chemical Biology, Published online: 27 June 2022; doi:10.1038/s41589-022-01068-6

Several venomous predators and pathogens use insulins to capture prey and to manipulate host physiology. This Review provides an overview of the discovery and potential biomedical application of these and other weaponized hormones found in nature.

Nature Chemical Biology, Published online: 27 June 2022; doi:10.1038/s41589-022-01054-y

Sea stars and sea cucumbers biosynthesize protective glycosylated steroids and triterpenes via divergent oxidosqualene cyclases (OSCs) that produce these distinct saponins in different species as well as in different tissues of a single species.

Nature Catalysis, Published online: 24 June 2022; doi:10.1038/s41929-022-00799-y

Although pyrene-containing molecules have been studied for their optical properties, the outcome of their incorporation into mechanically interlocked structures remains underexplored. Here, the authors install pyrene units into homo[2]catenanes and investigate the formation of long-lived triplet states, which can be exploited for photocatalysis.

Come together: Asymmetric aminocatalysis plays a pivotal role on the development in stereoselective transformations, synergistically combined with organo-, metal, photoredox and electrocatalysis. In this scenario, the HOMO-raising and LUMO-lowering activation of carbonyl compounds open new gateways to complex architectures and new sustainable reactivities. Last but not least, this research area will keep driving the development of the whole organocatalysis, toward its synergistic combination with other activation strategies.

Abstract

Synergistic catalysis offers the unique possibility of simultaneous activation of both the nucleophile and the electrophile in a reaction. A requirement for this strategy is the stability of the active species towards the reaction conditions and the two concerted catalytic cycles. Since the beginning of the century, aminocatalysis has been established as a platform for the stereoselective activation of carbonyl compounds through HOMO-raising or LUMO-lowering. The burgeoning era of aminocatalysis has been driven by a deep understanding of these activation and stereoinduction modes, thanks to the introduction of versatile and privileged chiral amines. The aim of this review is to cover recent developments in synergistic strategies involving aminocatalysis in combination with organo-, metal-, photo-, and electro-catalysis, focusing on the evolution of privileged aminocatalysts architectures.

Ecotoxicity: Organocatalysis is a widely used method of green and sustainable chemistry. The toxicity of a library of selected organocatalysts is determined, and it is found that aminocatalysts are of low ecotoxicity, but thioureas and squaramides prove about 10-fold more toxic. Thus, the latter compounds may be harmful to the environment and need more thorough (eco)toxicological evaluation.

Abstract

The importance of asymmetric organocatalysis in contemporary organic synthesis is widely acknowledged. However, there are practically no data on the environmental safety of organocatalysts, although this aspect is crucial for the sustainability of all new materials, chemicals, and technologies. To start to fill this data-gap, a library of 26 organocatalysts containing hydrogen-bonding catalysts [(thio)ureas and squaramides] and aminocatalysts (primary or secondary amines) was evaluated for their toxicity using the naturally luminescent Vibrio fischeri bacteria (ISO assay; one of the most widely used ecotoxicity tests). Thioureas and squaramides were shown to be relatively toxic: none of them was ranked as “not harmful” (i. e., half maximal effective concentration EC₅₀>100 mg L⁻¹), whereas the presence of the trifluoromethyl moiety increased their toxic effect. Importantly, the aminocatalysts, whose EC₅₀ values ranged from 25 to >300 mg L⁻¹, could be considered remarkably more environmentally safe or green alternatives.

The combination of small molecule catalysis and enzyme catalysis represents an underexploited area of research with huge potential in asymmetric synthetic chemistry due to both compatibility in reaction conditions and complementary reactivity. In this manuscript, we describe the telescopic synthesis of chiral nitro alcohols starting from commercially available benzaldehyde derivatives via the one-pot three-step chemoenzymatic cascade combination of a Wittig reaction, chiral thiourea-catalysed asymmetric conjugate addition, and a ketoreductase-mediated reduction to access the corresponding target compounds in moderate to excellent overall isolated yields (36-80%) and high diastereomeric and enantiomeric ratios (up to >97:3). This represents the first example of the combination of an organocatalysed asymmetric conjugate addition via iminium ion activation and a bioreduction step catalysed by ketoreductases.

Nature, Published online: 22 June 2022; doi:10.1038/s41586-022-04862-3

Global ocean microbiome survey reveals the bacterial family ‘Candidatus Eudoremicrobiaceae’, which includes some of the most biosynthetically diverse microorganisms in the ocean environment.

A PluriZyme with transaminase and esterase activities was constructed by combining computational and laboratory design methods. The enzyme can perform cascade reactions in a single protein scaffold. Experimental evidence is presented for the catalytic efficiency of both the native transaminase and the artificial esterase active site and their synergistic action to transform β-keto esters into enantiopure β-amino acids.

Abstract

Engineering dual-function single polypeptide catalysts with two abiotic or biotic catalytic entities (or combinations of both) supporting cascade reactions is becoming an important area of enzyme engineering and catalysis. Herein we present the development of a PluriZyme, TR₂E₂, with efficient native transaminase (k _cat: 69.49±1.77 min⁻¹) and artificial esterase (k _cat: 3908–0.41 min⁻¹) activities integrated into a single scaffold, and evaluate its utility in a cascade reaction. TR₂E₂ (pH_opt: 8.0–9.5; T _opt: 60–65 °C) efficiently converts methyl 3-oxo-4-(2,4,5-trifluorophenyl)butanoate into 3-(R)-amino-4-(2,4,5-trifluorophenyl)butanoic acid, a crucial intermediate for the synthesis of antidiabetic drugs. The reaction proceeds through the conversion of the β-keto ester into the β-keto acid at the hydrolytic site and subsequently into the β-amino acid (e.e. >99 %) at the transaminase site. The catalytic power of the TR₂E₂ PluriZyme was proven with a set of β-keto esters, demonstrating the potential of such designs to address bioinspired cascade reactions.

Spatial control over chemical reactions is a ubiquitous feature shared by all living organisms. In the present article, we describe the design of a proteinaceous, synthetic capsid based on the well-described bacterial nanocompartment encapsulin. Our engineered virus-like particle carries a dual functional artificial metalloenzyme (ArM) as non-native guest protein. This ArM, created from a fusion protein of HaloTag and monomeric rhizavidin, serves as catalyst for a fully bioorthogonal, linear, two-step reaction cascade. A ruthenium-catalyzed alloc deprotection is followed by a gold-catalyzed, ring-closing hydroamination reaction leading to indoles and phenanthridines with up to 67 % overall yield in aqueous solutions.

Nature Communications, Published online: 22 June 2022; doi:10.1038/s41467-022-31293-5

The activation of aziridines is typically achieved via reaction with strong Lewis acids or transition metals. Here, the authors report that cooperative Se ∙ ∙∙O and Se ∙ ∙∙N noncovalent interactions can activate sulfonyl-protected aziridines, which enables their use in cycloaddition reactions with nonactivated alkenes.

Nature Catalysis, Published online: 16 June 2022; doi:10.1038/s41929-022-00800-8

Flavin-dependent halogenases catalyse the challenging regioselective halogenation of aromatic compounds, but display low efficiency. Now, a tryptophan-halogenase with multiple catalytic improvements is obtained by engineering the intermediate transfer tunnel connecting the enzyme´s two active sites.

Come together: Asymmetric aminocatalysis plays a pivotal role on the development in stereoselective transformations, synergistically combined with organo-, metal, photoredox and electrocatalysis. In this scenario, the HOMO-raising and LUMO-lowering activation of carbonyl compounds open new gateways to complex architectures and new sustainable reactivities. Last but not least, this research area will keep driving the development of the whole organocatalysis, toward its synergistic combination with other activation strategies.

Abstract

Synergistic catalysis offers the unique possibility of simultaneous activation of both the nucleophile and the electrophile in a reaction. A requirement for this strategy is the stability of the active species towards the reaction conditions and the two concerted catalytic cycles. Since the beginning of the century, aminocatalysis has been established as a platform for the stereoselective activation of carbonyl compounds through HOMO-raising or LUMO-lowering. The burgeoning era of aminocatalysis has been driven by a deep understanding of these activation and stereoinduction modes, thanks to the introduction of versatile and privileged chiral amines. The aim of this review is to cover recent developments in synergistic strategies involving aminocatalysis in combination with organo-, metal-, photo-, and electro-catalysis, focusing on the evolution of privileged aminocatalysts architectures.

A visible light mediated Arbuzov type reaction of thiophenols and phosphites to access phosphorothioates under mild metal-free conditions was demonstrated.

Abstract

We hereby disclose, a visible light mediated addition of sulfenyl radicals to trialkyl phosphites to access functionalized phosphorothioates. The use of cheap and readily available Eosin Y as a photocatalyst under mild energy efficient conditions bypassing the use of external oxidants forms the chief highlight of the work. The protocol is scalable and mechanistic studies indicate that the reaction proceeds through an ionic-Arbuzov like pathway from phosphoranyl radicals.

Diastereomeric intermediates can be separated by ion mobility mass spectrometry. Monitoring of the kinetics of the intermediates allows the prediction of the overall reaction enantioselectivity. The experiments can be performed in a small scale and do not require an isolation of the products.

Abstract

Enantioselective reactions are at the core of chemical synthesis. Their development mostly relies on prior knowledge, laborious product analysis and post-rationalization by theoretical methods. Here, we introduce a simple and fast method to determine enantioselectivities based on mass spectrometry. The method is based on ion mobility separation of diastereomeric intermediates, formed from a chiral catalyst and prochiral reactants, and delayed reactant labeling experiments to link the mass spectra with the reaction kinetics in solution. The data provide rate constants along the reaction paths for the individual diastereomeric intermediates, revealing the origins of enantioselectivity. Using the derived kinetics, the enantioselectivity of the overall reaction can be predicted. Hence, this method can offer a rapid discovery and optimization of enantioselective reactions in the future. We illustrate the method for the addition of cyclopentadiene (CP) to an α,β-unsaturated aldehyde catalyzed by a diarylprolinol silyl ether.

A small artificial hydrolase that mimics the active centre of chymotrypsin and N-terminal hydrolases is able to perform, for the first time, the transesterification of ethyl acetate with methanol under neutral conditions and at room temperature. This artificial enzyme also catalysed the transesterification of important neurotransmitter acetylcholine into methyl acetate and choline.

Abstract

The synthesis of small molecules able to mimic the active site of hydrolytic enzymes has been largely pursued in recent decades. The high reaction rates and specificity shown by natural hydrolases present an attractive target, and yet the preparation of suitable small-molecule mimics remains challenging, requiring activated substrates to achieve productive outcomes. Here we present small synthetic artificial enzymes which mimic the catalytic site and the oxyanion hole of chymotrypsin and N-terminal hydrolases and are able to perform, for the first time, the transesterification of a non-activated ester such as ethyl acetate with methanol under mild and neutral reaction conditions.

Isothiouronyl radical cations have been identified as a new class of radical catalysts for the covalent activation of vinylcyclopropanes. Their generation by photoredox catalysis from N,N,N,N-tetrasubstituted thioureas provides a modular, versatile and practical platform to achieve covalent radical catalysis.

Abstract

Thiyl radicals offer unique catalytic patterns for the direct covalent activation of alkenes. However, important limitations in terms of structural diversity and handling have hampered the routine use of thiyl radicals in covalent radical catalysis. Herein, we report a new class of cationic sulfur-centered radicals to achieve covalent radical catalysis. Their generation from highly modular thioureas by photoredox catalysis make their utilization very simple and reliable. The synthetic potential and the versatility of the catalytic system were finally evaluated in a (3+2)-radical cascade between vinylcyclopropanes and olefins.

Herein we describe a method for combining supramolecular catalysis with imininum-based organocatalysis in the Diels–Alder cycloaddition reaction. Notably, both cage and L-proline are required for the reaction to occur, implying that encap-sulation of the substrates and co-catalyst are necessary for the reaction to occur. We explore the substrate scope for a va-riety of E-cinnamaldehydes and dienes. Finally, we probe the supramolecular assembly processes responsible for the observed catalysis using NMR spectroscopic methods, determining that the reaction is negative order in the cinnamalde-hyde substrate and experiences product inhibition.