Braca

Nature Chemistry, Published online: 28 February 2024; doi:10.1038/s41557-024-01463-7

Developing a generalizable method for blocking and rescuing tryptophan (Trp) interactions would enable the gain-of-function manipulation of various Trp-containing proteins but has so far been challenging. Now a genetically encoded N1-vinyl-caged Trp capable of rapid and bioorthogonal decaging enables site-specific activation of Trp on a protein of interest within living cells.

Nature Synthesis, Published online: 07 March 2024; doi:10.1038/s44160-024-00492-x

Multicomponent catalytic reactions that generate enantioenriched boronic esters are underdeveloped. Now an N-heterocyclic carbene–nickel catalyst promotes enantioselective alkene 1,2-carboboration to access multifunctional alkylboronates, bearing a tertiary or quaternary β-stereocentre.

Synlett
DOI: 10.1055/a-2256-2980

Presented here is a detailed account of the development and implementation of macrocyclic cobaloxime complexes as sulfur-free, catalytic chain transfer agents (CTAs) in crosslinking photopolymerizations. Although much of this review is dedicated to understanding the fundamentals of catalytic chain transfer (CCT) in photopolymerizations, its impact on network topology and resultant mechanical properties, future goals of applying this technology to multimaterial 3D printing are also discussed. It is our long-term ambition for catalytic, sulfur-free CTAs to supplant existing consumptive, sulfur-based agents to provide new, unexplored, and not currently possible to fabricate photopolymeric materials with a specific eye towards application in dentistry, additive manufacturing, and responsive materials.1 Introduction2 History of Catalytic Chain Transfer (CCT)3 Understanding Catalyst Purity and Chain Transfer Activity4 Evidencing CCT in a Crosslinking Photopolymerization5 Comparing Cobalt(II)-Catalysts to Other Relevant CTAs6 Performance of Cobalt(II)-Catalysts in Commercial Resins7 Limitations of Approach and Looking Forward
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

To unravel why computational design fails in creating viable enzymes, while directed evolution (DE) succeeds, our research delves into the laboratory evolution of Protoglobin. DE has adapted this protein to efficiently catalyze carbene transfer reactions. We show that the previously proposed enhanced substrate access and binding alone cannot account for increased yields during DE. The 3D electric field in the entire active site is tracked through protein dynamics, clustered using the affinity propagation algorithm, and subjected to principal component analysis. This analysis reveals notable changes in the electric field with DE, where distinct field topologies influence transition state energetics and mechanism. A chemically meaningful field component emerges and takes the lead during DE and facilitates crossing the barrier to carbene transfer. Our findings underscore intrinsic electric field dynamic's influence on enzyme function, the ability of the field to switch mechanisms within the same protein, and the crucial role of the field in enzyme design.

Cerium photoredox catalysis has emerged as a powerful strategy to activate molecules under mild conditions. Radical intermediates are formed using visible light and simple complexes of the earth-abundant lanthanide. However, it remains a major challenge to achieve stereocontrol in these reactions. Here, we report an artificial photoenzyme enabling this chemistry inside a protein. We utilize a de novo designed protein scaffold that tightly binds lanthanide ions in its central cavity. Upon visible-light irradiation, the cerium-dependent enzyme catalyzes the radical C–C bond cleavage of 1,2-diols in aqueous solution. Protein engineering led to variants with improved photostability and initial stereoselectivity. The photoenzyme cleaves a range of aromatic and aliphatic substrates, including lignin surrogates. Surface display of the protein scaffold on E. coli facilitates whole-cell photobiocatalysis. Furthermore, we show that also natural lanthanide-binding proteins are suitable for this approach. Our study thus demonstrates a new-to-nature enzymatic photoredox activity with broad catalytic potential.

Nature Communications, Published online: 04 March 2024; doi:10.1038/s41467-024-46123-z

The authors previously showed that a histidine nucleophile and a flexible arginine can work in synergy to accelerate the Morita Baylis-Hillman (MBH) reaction. Here, they report another efficient MBHase that employs a non-canonical Nδ-methylhistidine nucleophile paired with a catalytic glutamate, providing an alternative mechanistic solution for MBH catalysis.

Nature Communications, Published online: 02 March 2024; doi:10.1038/s41467-024-46188-w

Epoxides are prominent small-ring O-heterocycles found in a variety of bioactive natural products and pharmaceuticals. Here, the authors report a silver carbene strategy to achieve O-to-C atom exchange of epoxides in a single step, affording diverse fluoroalkylcyclopropanes.

Nature Chemistry, Published online: 01 March 2024; doi:10.1038/s41557-024-01472-6

Although generally perceived as an old-fashioned and unselective tool to build molecules, the photochemistry community is now re-discovering the power of UV light and is using key mechanistic information to develop new catalytic processes driven by visible light. This Perspective discusses the progress and impact of UV light in organic synthesis.

Communications Chemistry, Published online: 28 February 2024; doi:10.1038/s42004-024-01130-5

Ipatasertib is a potent Akt (protein kinase B) inhibitor synthesized via a chemoenzymatic process. Here, the authors use mutational scanning and algorithm-aided enzyme engineering to optimize a ketoreductase from Sporidiobolus salmonicolor and generate a 10-amino acid substituted variant exhibiting a 64-fold higher kcat and improved yield for the relevant alcohol intermediate, with ≥ 98% conversion and a diastereomeric excess of 99.7% (R,R-trans) from 100 g L−1 ketone after 30 h.

Synlett
DOI: 10.1055/a-2268-4678

The manganese(I)-catalyzed allylation of the amino acid tryptophan is realized under exceedingly mild conditions using water as a sustainable and non-hazardous reaction medium, instead of classical organic solvents, with great potential for green and sustainable chemistry. Synthetically useful α,β-unsaturated esters can be accessed by reaction with Morita–Baylis–Hillman (MBH) adducts following a fast C–H activation approach. The robustness of this procedure is reflected by kinetic analysis at different reaction temperatures and reduced catalyst loadings are employed.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

A cooperative NHC/nickel catalytic methodology has been developed for the synthesis of ketones employing aromatic aldehydes and tertiary alkyl iodides. All key steps of the postulated catalytic cycle were validated with comprehensive stoichiometric and electrochemical studies, including reduction of NiII by the deprotonated Breslow intermediate, Ni0 promoted halogen-atom abstraction to generate transient tertiary alkyl radicals and coupling between the latter with the persistent acyl thiazolium radical intermediate. Such broadly proposed and accepted, yet elusive, acyl thiazolium radical intermediate has been isolated and stud-ied by a single-crystal X-ray diffraction study.

Nature Catalysis, Published online: 20 February 2024; doi:10.1038/s41929-024-01109-4

The direct cross-electrophile coupling of (hetero)aryl halides and pseudohalides is challenging. Now this reaction is facilitated by a visible light-induced palladium catalytic system that differentiates the reactants on the basis of the bond dissociation enthalpy affording unsymmetrical (hetero)biaryls.

Relying on ubiquitous alkenes, carboamination reactions enable the difunctionalization of the double bond by the concurrent formation of a C–N and a C–C single bond. In the past years, several groups have reported on elegant strategies for the carboamination of alkenes relying on homogeneous catalysts or enzymes. Herein, we report on an artificial metalloenzyme for the enantioselective carboamination of dihydrofuran. Genetic optimization, combined with a Bayesian optimization of catalytic performance, afforded the disubstituted tetrahydrofuran product in up to 22 TON and 85% ee. X-ray analysis of the evolved artificial carboaminase shed light on critical amino acid residues that affect catalytic performance.

Nature Communications, Published online: 17 February 2024; doi:10.1038/s41467-024-45867-y

Stoichiometric amounts of metal reductant and the requirement of a directing group limit the application of transition metal-catalyzed reductive difunctionalization of alkenes with alkyl halides. Here, the authors report a reductive difunctionalization of alkenes via a radical-anion relay with Na2S2O4 as both reductant and sulfone-source.

Nature Chemistry, Published online: 13 February 2024; doi:10.1038/s41557-023-01435-3

The use of biocatalysis to support early-stage drug discovery campaigns remains largely untapped. Here, engineered biocatalysts enable the synthesis of sp3-rich polycyclic compounds through an intramolecular cyclopropanation of benzothiophenes, affording a class of complex scaffolds potentially useful for fragment-based drug discovery campaigns.

Antimicrobial resistance is an urgent global public health problem that has made the search for new antibiotics essential. Ribosomally synthesized and post-translationally modified peptides are a promising new class of antibiotics and in this work, we report site-selective modification of their dehydroamino acids by β-amination in order to increase water solubility: the singly modified thiopeptide Thiostrepton showed an increase up to 35-fold and minimum inhibitory concentration tests demonstrated that the antimicrobial activity was still good, albeit lower than the natural peptide.

Abstract

We report the efficient and site selective modification of non-canonical dehydroamino acids in ribosomally synthesized and post-transationally modified peptides (RiPPs) by β-amination. The singly modified thiopeptide Thiostrepton showed an up to 35-fold increase in water solubility, and minimum inhibitory concentration (MIC) assays showed that antimicrobial activity remained good, albeit lower than the unmodified peptide. Also the lanthipeptide nisin could be modified using this method.