Braca

The evolution of a promiscuous enzyme for its various activities often results in catalytically specialized variants. This is an important natural mechanism to ensure the proper functioning of natural metabolic networks. It also acts as both a curse and blessing for enzyme engineers, where enzymes that have undergone directed evolution may exhibit exquisite selectivity at the expense of a diminished overall catalytic repertoire. We previously performed two independent directed evolution campaigns on a promiscuous artificial enzyme that leverages the unique properties of a non-canonical amino acid (ncAA) para- aminophenylalanine (pAF) as catalytic residue, resulting in two evolved variants which are both catalytically specialized. Here, we combine mutagenesis, crystallography and computation to reveal the molecular basis of the specialization phenomenon. In one evolved variant, an unexpected change in quaternary structure biases substrate dynamics to promote enantioselective catalysis, whilst the other demonstrates synergistic cooperation between natural side chains and the pAF residue to form semi-synthetic catalytic machinery. Our analysis provides valuable insights for the future engineering of effective artificial enzymes which employ either the widely used LmrR scaffold or pAF catalytic residue.

Nature, Published online: 29 August 2024; doi:10.1038/s41586-024-07988-8

Synthesis of non-canonical amino acids through dehydrogenative tailoring

Nature Chemistry, Published online: 28 August 2024; doi:10.1038/s41557-024-01608-8

Catalytic asymmetric radical dearomatization has remained a daunting task due to the challenges in exerting stereocontrol over highly reactive radical intermediates. Now, using metalloredox biocatalysis, new-to-nature radical dearomatases P450rad1–P450rad5 have been engineered to facilitate asymmetric dearomatization of a broad spectrum of aromatic substrates, including indoles, pyrroles and phenols.

Gold, in contrast to other transition metals, offers a unique reactivity profile and has emerged as an efficient tool in the field of synthetic organic chemistry. This review will focus on recent advances in gold-catalyzed Heck and Suzuki-type reactions, particularly those facilitated by photocatalysts and ligand design.

Abstract

Transition metal-catalyzed Suzuki and Heck reactions are two of the most common carbon-carbon bond formation reactions. Gold, unlike other transition metals (Pd, Ni, and Cu), offers unique reactivity profiles, and has emerged as an efficient tool in the field of synthetic organic chemistry. This mini-review focused on the recent work in gold-catalyzed Heck and Suzuki-type reactions, especially by photocatalysts or ligand design, which show reactivities and features distinct from other transition metals. These discoveries will further facilitate the development of gold redox catalysis as well as applications in organic synthesis, biochemistry, and medicinal chemistry.

Publication date: 17 October 2024

Source: Tetrahedron, Volume 166

Author(s): Zixiu Liu, Xinhan Li, Qingling Ou, Yunyan Meng, Jianbin Xu, Baomin Fan

The trifluoromethyl (–CF3) group represents a highly prevalent functionality in pharmaceuticals. Over the past few decades, significant advances have been made in the development of synthetic methods for trifluoromethylation. In contrast, there are currently no metalloenzymes known to catalyze the formation of C(sp3)‒CF3 bonds. In this work, we demonstrate that a nonheme iron enzyme, hydroxymandelate synthase from Amycolatopsis orientalis (AoHMS), is capable of generating CF3 radicals from hypervalent iodine(III) reagents and directing them for enantioselective alkene trifluoromethyl azidation. A high-throughput screening (HTS) platform based on Staudinger ligation was established, enabling the rapid evaluation of AoHMS variants for this abiological transformation. The final optimized variant accepts a range of alkene substrates, producing the trifluoromethyl azidation products in up to 73% yield and 96:4 enantiomeric ratio (e.r.). The biocatalytic platform can be further extended to alkene pentafluoroethyl azidation and diazidation by altering the iodine(III) reagent. In addition, anion competition experiments provide insights into the radical rebound process for this abiological transformation. This study not only expands the catalytic repertoire of metalloenzymes for radical transformations but also creates a new enzymatic space for organofluorine synthesis.

Nature Chemical Biology, Published online: 16 August 2024; doi:10.1038/s41589-024-01707-0

Boron is a common element found in various minerals; however, it is not used in life-creating machinery in nature. In a new study, boron enzymes have been created by introducing a boronic acid-containing non-canonical amino acid into an artificial enzyme scaffold. Further development via directed evolution enabled the selection of new-to-nature stereoselective chemistry.

Publication date: 8 August 2024

Source: Chem, Volume 10, Issue 8

Author(s): Zhi Zou, Bradley Higginson, Thomas R. Ward

This study demonstrates the efficient synthesis of various heterocycles using the metal hydrogen atom transfer (MHAT)/ radical-polar crossover (RPC) method, emphasizing its versatility under mild conditions with high functional group tolerance. By distinguishing between cyclization and annulation, we underscore the complexity and efficiency of this approach in constructing intricate molecular architectures. Notably, the incorporation of an acetone solvent in the formation of cyclic acetal dioxanes from homoallylic alcohols reveals a novel annulation mechanism. Extensive substrate scope analysis and density functional theory calculations provide insights into reaction pathways, highlighting the critical role of cationic alkylcobalt(IV) intermediates and collidine in product selectivity. This study elucidates the mechanisms of the MHAT/RPC method and showcases its potential as a robust alternative to conventional synthetic strategies.

The onset of Darwinian evolution represents a key step in the transition of chemical systems into living ones. Here, we show the emergence of Darwinian evolution in two systems of self-replicating molecules, where natural selection favors replicator mutants best capable of catalyzing the production of the precursors required for their own replication. Such selection for protometabolic activity was observed in a system where trimer and hexamer replicators compete for common resources, as well as in a system of different hexamer replicator mutants. An out-of-equilibrium replication-destruction regime was implemented in a flow reactor, where replication from continuously supplied dithiol building blocks needs to keep up with “destruction” by outflow. Selection occurred based on the ability of the mutants to activate a cofactor that photocatalytically produces singlet oxygen which, in turn, enhances the rate by which dithiol building blocks are converted into disulfide-based replicator precursors. Selection was based on a functional trait (catalytic activity) opening up Darwinian evolution as a tool for catalyst development. This work functionally integrates self-replication with protometabolism and Darwinian evolution and marks a further advance in the de-novo synthesis of life.

Nature, Published online: 08 August 2024; doi:10.1038/d41586-024-02557-5

Stress leads to disarray of the gut microbiome, which in turn causes inflammation and a drop in the body’s ability to fend off infection.

Asymmetric Catalysis. The design and evolution of an enzyme for the asymmetric Michael addition of cyclic ketones to nitroolefins by enamine catalysis is reported by Zhi Zhou et al. in their Communication (e202404312).

A cobalt-catalyzed intramolecular Markovnikov hydroalkoxycarbonylation and hydroaminocarbonylation of unactivated alkenes has been developed, enabling highly chemo- and regioselective synthesis of α-alkylated γ-lactones as well as α-alkylated γ-lactams under mild reaction conditions. Mechanistic studies suggest the reaction proceeds through a CO-mediated hydrogen atom transfer (HAT) and radical-polar crossover (RPC) process.

Abstract

A cobalt-catalyzed intramolecular Markovnikov hydroalkoxycarbonylation and hydroaminocarbonylation of unactivated alkenes has been developed, enabling highly chemo- and regioselective synthesis of α-alkylated γ-lactones and α-alkylated γ-lactams in good yields. The mild reaction conditions allow use of mono-, di- and trisubstituted alkenes bearing a variety of functional groups. Preliminary mechanistic studies suggest the reaction proceeds through a CO-mediated hydrogen atom transfer (HAT) and radical-polar crossover (RPC) process, in which a cationic acylcobalt(IV) complex is proposed as the key intermediate.

Nature Synthesis, Published online: 05 August 2024; doi:10.1038/s44160-024-00630-5

Publisher Correction: Combining an artificial metathase with a fatty acid decarboxylase in a whole cell for cycloalkene synthesis

Abstract

The rapid development of photo-synergistic transition metal catalytic systems has provided a green paradigm to complement thermal transition metal catalytic methods. However, the most commonly used iridium or ruthenium complexes involve expensive in nature, in contrast to the abundant copper elements in the earth's crust, which are highly valued for their unique electronic structure and light-absorbing properties. Recently, the application of copper and photocatalytic synergistic strategies in radical cyclization reactions has progressed considerably, leading to a renaissance in the synthesis of functional natural products, drugs and their analogues, but summary work addressing this aspect has not been reported. In this review, we briefly analyze the effect of ligand choice on copper complexes and some inorganic copper salts and even on light sources. We then summarize the copper and photocatalytic synergistic strategies in radical cyclization reactions and classify them into three categories, C, N and O radicals, according to the class of the central atom of the radical in each work, and in each category will be elaborated in turn from coordination cyclization via Cu catalysts, direct radical cyclization and other cyclization mode. For individual more complex reactions, the mechanisms are explored and briefly discussed.

The catalytic repertoire of nature has been expanded over the past decades by the introduction of artificial metalloenzymes. These are enzymes containing a synthetic metal complex or a non-native metal ion. However, combining noble metal catalysis and enzymes remains challenging due to the lack of suitable ligands to bind these complexes. So far, noble metal artificial metalloenzyme design mostly involves in vitro approaches of ligand anchoring, like covalent modification of a cysteine residue or via supramolecular assembly. Here, we show a facile strategy to anchor a variety of 4d and 5d-transition metal complexes via genetic incorporation of a thiophenolic metal-binding ligand. We created a methodology to efficiently incorporate 4-mercaptophenylalanine in a protein scaffold using the stop codon suppression technology. The incorporated non-canonical amino acid was capable of binding a variety of noble metal complexes. To showcase the catalytic applications of this methodology, we developed an artificial hydroaminase by binding gold ions to the thiophenol-containing protein. The benefit of in vivo incorporation of the ligand is demonstrated by the susceptibility of catalytic activity to the microenvironment around the metal site, which can be modulated by changing the position of the ligand within the protein or by mutation of residues in its proximity.