LongLarf

Publication date: 8 February 2024

Source: Chem, Volume 10, Issue 2

Author(s): George H. Hutchins, Sebastian Kiehstaller, Pascal Poc, Abigail H. Lewis, Jisun Oh, Raya Sadighi, Nicholas M. Pearce, Mohamed Ibrahim, Ivana Drienovská, Anouk M. Rijs, Saskia Neubacher, Sven Hennig, Tom N. Grossmann

Nature Synthesis, Published online: 02 November 2023; doi:10.1038/s44160-023-00431-2

Atroposelective metathesis catalyzed by artificial enzymes in aqueous solution would provide an attractive and sustainable route to drug molecules and other compounds of interest. We demonstrate that this is possible using artificial metalloenzymes harboring a ruthenium cofactor.

Abstract

Atropisomers – separable conformers that arise from restricted single-bond rotation – are frequently encountered in medicinal chemistry. However, preparing such compounds with the desired configuration can be challenging. Herein, we present a biocatalytic strategy for achieving atroposelective synthesis relying on artificial metalloenzymes (ArMs). Based on the biotin-streptavidin technology, we constructed ruthenium-bearing ArMs capable of producing atropisomeric binaphthalene compounds through ring-closing metathesis in aqueous media. Further, we show that atroposelectivity can be fine-tuned by engineering two close-lying amino acid residues within the streptavidin host protein. The resulting ArMs promote product formation with enantiomeric ratios of up to 81 : 19, while small-molecule catalysts for atroposelective metathesis under aqueous reaction conditions are yet unknown. This study represents the first demonstration that stereoselective metathesis can be achieved by an artificial metalloenzyme.

Together we are strong: Covalent homodimerization by disulfide engineering of the tryptophan halogenases Thal and PyrH leads to a significant increase in thermostability while retaining activity.

Abstract

Flavin-dependent halogenases allow halogenation of electron-rich aromatic compounds under mild reaction conditions even at electronically unfavored positions with high regioselectivity. In order to expand the application of halogenases, the enzymes need to be improved in terms of stability and efficiency. A previous study with the tryptophan 6-halogenase Thal demonstrated that thermostable Thal variants tend to form dimers in solution while the wild type is present as a monomer. Based on this a dimeric Thal variant was generated that is covalently linked by disulfide bonds. Introducing two cysteine residues at the dimer interface resulted in the variant Thal CC with significantly increased thermostability (▵T ₅₀=15.7 K) and stability over time at elevated temperature compared to the wild type. By introducing the homologous mutations into the tryptophan 5-halogenase PyrH, we were able to show that the stabilization by covalent dimerization can also be transferred to other halogenases. Moreover, it was possible to further increase the thermostability of PyrH by inserting cysteine mutations at alternative sites of the dimer interface.

Nature, Published online: 01 November 2023; doi:10.1038/s41586-023-06613-4

This review emphasizes and comprehensively analyses representative examples of palladium(II)-catalyzed late-stage C−H activation reactions and demonstrates their efficacy in converting C−H bonds at multiple positions within drug (derivative) molecules into diverse functional groups. Specifically, this study elucidates the notable strides made in the realm of late-stage C−H activation of drug (derivatives) molecules employing Pd (II) catalysts.

Abstract

This review comprehensively analyses representative examples of Pd(II)-catalyzed late-stage C−H activation reactions and demonstrates their efficacy in converting C−H bonds at multiple positions within drug (derivative) molecules into diverse functional groups. These transformative reactions hold immense potential in medicinal chemistry, enabling the efficient and selective functionalization of specific sites within drug molecules, thereby enhancing their pharmacological activity and expanding the scope of potential drug candidates. Although notable articles have focused on late-stage C−H functionalization reactions of drug-like molecules using transition-metal catalysts, reviews specifically focusing on late-stage C−H functionalization reactions of drug (derivative) molecules using Pd(II) catalysts are required owing to their prominence as the most widely utilized metal catalysts for C−H activation and their ability to introduce a myriad of functional groups at specific C−H bonds. The utilization of Pd-catalyzed C−H activation methodologies demonstrates impressive success in introducing various functional groups, such as cyano (CN), fluorine (F), chlorine (Cl), aromatic rings, olefin, alkyl, alkyne, and hydroxyl groups, to drug (derivative) molecules with high regioselectivity and functional-group tolerance. These breakthroughs in late-stage C−H activation reactions serve as invaluable tools for drug discovery and development, thereby offering strategic options to optimize drug candidates and drive the exploration of innovative therapeutic solutions.

The multi-step reduction of carboxy groups to methyl groups commonly used in organic synthesis is simplified by a new metal-free catalyst system. It uses boronic acids to catalyze the single-step reduction of esters, carboxylic acids and carbamates to methyl groups. High-yield, multifunctional product formation is achieved under mild conditions using ammonia borane as the hydrogen donor.

Abstract

Carboxy to methyl reduction is an important transformation in organic synthesis, yet existing methodologies often require multi-step procedures or use hazardous metal hydrides. Herein, a metal-free catalytic system is reported for the one-step reduction of esters, carboxylic acids, and carbamates to a methyl group, in the presence of catalytic amounts of boronic acids. By using ammonia borane as a hydrogen donor, a wide range of products bearing different functional groups can be obtained in high yields under relatively mild conditions. Mechanistic studies and control experiments elucidate the complexity of the mechanism and provide an explanation for the observed selectivity.

Sustainable strategies inspired by the innate structural features of lignin were developed for the synthesis of diverse biologically active compounds, including tetrahydroisoquinolines, quinazolinones, dopamine and the natural product tetrahydropapaveroline. The synthetic approach enabled the rapid assessment of relevant biological activities through in vitro and in vivo studies and computational similarity searches, with multiple promising hits identified.

Abstract

Deriving active pharmaceutical agents from renewable resources is crucial to increasing the economic feasibility of modern biorefineries and promises to alleviate critical supply-chain dependencies in pharma manufacturing. Our multidisciplinary approach combines research in lignin-first biorefining, sustainable catalysis, and alternative solvents with bioactivity screening, an in vivo efficacy study, and a structural-similarity search. The resulting sustainable path to novel anti-infective, anti-inflammatory, and anticancer molecules enabled the rapid identification of frontrunners for key therapeutic indications, including an anti-infective against the priority pathogen Streptococcus pneumoniae with efficacy in vivo and promising plasma and metabolic stability. Our catalytic methods provided straightforward access, inspired by the innate structural features of lignin, to synthetically challenging biologically active molecules with the core structure of dopamine, namely, tetrahydroisoquinolines, quinazolinones, 3-arylindoles and the natural product tetrahydropapaveroline. Our diverse array of atom-economic transformations produces only harmless side products and uses benign reaction media, such as tunable deep eutectic solvents for modulating reactivity in challenging cyclization steps.

The stepwise dearomative functionalization reaction of pyridines generates highly substituted piperidines, featuring diverse functional handles, with excellent site-, regio-, and diastereoselectivity. The origin of the unprecedented selectivities and additional insights into the reaction mechanism are discussed based on combined experimental mechanistic studies and density functional theory computations.

Abstract

Nitrogen heterocycles play a vital role in pharmaceuticals and natural products, with the six-membered aromatic and aliphatic architectures being commonly used. While synthetic methods for aromatic N-heterocycles are well-established, the synthesis of their aliphatic functionalized analogues, particularly piperidine derivatives, poses a significant challenge. In that regard, we propose a stepwise dearomative functionalization reaction for the construction of highly decorated piperidine derivatives with diverse functional handles. We also discuss challenges related to site-selectivity, regio- and diastereoselectivity, and provide insights into the reaction mechanism through mechanistic studies and density functional theory computations.

Despite the unique reactivity of vitamin B12 and its derivatives, B12-dependent enzymes remain underutilized in biocatalysis. In this study, we repurpose the B12-dependent transcription factor CarH to enable non-native radical cyclization reactions. An engineered variant of this enzyme, CarH*, catalyzes the formation γ- and δ-lactams via either redox-neutral or reductive ring closure with marked enhancement of reactivity and selectivity relative to the free B12 cofactor. CarH* also catalyzes an unusual spirocyclization via dearomatization of pendant arenes to produce bicyclic 1,3-diene products instead of 1,4-dienes provided by existing methods. These results and associated mechanistic studies highlight the importance of protein scaffolds for controlling the reactivity of B12 and expanding the synthetic utility of B12-dependent enzymes.

Broad screening of the substrate specificity of SIRT7 revealed a strong preference for the cleavage of long-chain acyllysine modifications. The activity was substantially increased in the presence of oligonucleotides or nucleosome particles. Finally, random nonstandard peptide integrated discovery (RaPID) delivered a cyclopeptide with potency in the sub-micromolar range and selectivity for SIRT7, which binds and stabilizes SIRT7 in cells.

Abstract

The sirtuins are NAD⁺-dependent lysine deacylases, comprising seven isoforms (SIRT1–7) in humans, which are involved in the regulation of a plethora of biological processes, including gene expression and metabolism. The sirtuins share a common hydrolytic mechanism but display preferences for different ϵ-N-acyllysine substrates. SIRT7 deacetylates targets in nuclei and nucleoli but remains one of the lesser studied of the seven isoforms, in part due to a lack of chemical tools to specifically probe SIRT7 activity. Here we expressed SIRT7 and, using small-angle X-ray scattering, reveal SIRT7 to be a monomeric enzyme with a low degree of globular flexibility in solution. We developed a fluorogenic assay for investigation of the substrate preferences of SIRT7 and to evaluate compounds that modulate its activity. We report several mechanism-based SIRT7 inhibitors as well as de novo cyclic peptide inhibitors selected from mRNA-display library screening that exhibit selectivity for SIRT7 over other sirtuin isoforms, stabilize SIRT7 in cells, and cause an increase in the acetylation of H3 K18.