An overview of late-stage functionalization in today’s drug discovery

Discovery and substrate specificity engineering of nucleotide halogenases

C2'-halogenation has been recognized as an essential modification to enhance the drug-like properties of nucleotide analogs. The direct C2'-halogenation of the nucleotide 2'-deoxyadenosine-5'-monophosphate (dAMP) has recently been achieved using the Fe(II)/α-ketoglutarate-dependent nucleotide halogenase AdaV. However, the limited substrate scope of this enzyme hampers its broader applications. In this study, we report two halogenases capable of halogenating 2'-deoxyguanosine monophosphate (dGMP), thereby expanding the family of nucleotide halogenases. Computational studies reveal that nucleotide specificity is regulated by the binding pose of the phosphate group. Based on these findings, we successfully engineered the substrate specificity of these halogenases by mutating second-sphere residues. This work expands the toolbox of nucleotide halogenases and provides insights into the regulation mechanism of nucleotide specificity.

Leveraging Language Model Multitasking To Predict C-H Borylation Selectivity

C-H borylation is a high-value transformation in the synthesis of lead candidates for the pharmaceutical industry because a wide array of downstream coupling reactions is available. However, predicting its regioselectivity, especially in drug-like molecules that may contain multiple heterocycles, is not a trivial task. Using a data set of borylation reactions from Reaxys, we explored how a language model originally trained on USPTO_500_MT, a broad-scope set of patent data, can be used to predict the C-H borylation reaction product in different modes: product generation and site reactivity classification. Our fine-tuned T5Chem multitask language model can generate the correct product in 79% of cases. It can also classify the reactive aromatic C-H bonds with 95% accuracy and 88% positive predictive value, exceeding purpose-developed graph-based neural networks.

Discovery of N-X anomeric amides as electrophilic halogenation reagents

Electrophilic halogenation is a widely used tool employed by medicinal chemists to either pre-functionalize molecules for further diversity or incorporate a halogen atom into drugs or drug-like compounds to solve metabolic problems or modulate off-target effects. Current methods to increase the power of halogenation rely on either the invention of new reagents or activating commercially available reagents with various additives such as Lewis or Brønsted acids, Lewis bases and hydrogen-bonding activators. There is a high demand for new reagents that can halogenate otherwise unreactive compounds under mild conditions. Here we report the invention of a class of halogenating reagents based on anomeric amides, taking advantage of the energy stored in the pyramidalized nitrogen of N-X anomeric amides as a driving force. These robust halogenating methods are compatible with a variety of functional groups and heterocycles, as exemplified on over 50 compounds (including 13 gram-scale examples and 1 flow chemistry scale-up).

Late-Stage Saturation of Drug Molecules

The available methods of chemical synthesis have arguably contributed to the prevalence of aromatic rings, such as benzene, toluene, xylene, or pyridine, in modern pharmaceuticals. Many such sp2-carbon-rich fragments are now easy to synthesize using high-quality cross-coupling reactions that click together an ever-expanding menu of commercially available building blocks, but the products are flat and lipophilic, decreasing their odds of becoming marketed drugs. Converting flat aromatic molecules into saturated analogues with a higher fraction of sp3 carbons could improve their medicinal properties and facilitate the invention of safe, efficacious, metabolically stable, and soluble medicines. In this study, we show that aromatic and heteroaromatic drugs can be readily saturated under exceptionally mild rhodium-catalyzed hydrogenation, acid-mediated reduction, or photocatalyzed-hydrogenation conditions, converting sp2 carbon atoms into sp3 carbon atoms and leading to saturated molecules with improved medicinal properties. These methods are productive in diverse pockets of chemical space, producing complex saturated pharmaceuticals bearing a variety of functional groups and three-dimensional architectures. The rhodium-catalyzed method tolerates traces of dimethyl sulfoxide (DMSO) or water, meaning that pharmaceutical compound collections, which are typically stored in wet DMSO, can finally be reformatted for use as substrates for chemical synthesis. This latter application is demonstrated through the late-stage saturation (LSS) of 768 complex and densely functionalized small-molecule drugs.

Late-stage meta-C-H alkylation of pharmaceuticals to modulate biological properties and expedite molecular optimisation in a single step

Catalysed C-H activation has emerged as a transformative platform for molecular synthesis and provides new opportunities in drug discovery by late-stage functionalisation (LSF) of complex molecules. Notably, small aliphatic motifs have gained significant interest in medicinal chemistry for their beneficial properties and applications as sp3-rich functional group bioisosteres. In this context, we disclose a versatile strategy with broad applicability for the ruthenium-catalysed late-stage meta-C(sp2)-H alkylation of pharmaceuticals. This general protocol leverages numerous directing groups inherently part of bioactive scaffolds to selectivity install a variety of medicinally relevant bifunctional alkyl units within drug compounds. Our strategy enables the direct modification of unprotected lead structures to quickly generate an array of pharmaceutically useful analogues without resorting to de novo syntheses. Moreover, productive late-stage modulation of key biological characteristics of drug candidates upon remote C-H alkylation proves viable, highlighting the major benefits of our approach to offer in drug development programmes.

Light-Driven Radiochemistry with Fluorine-18, Carbon-11 and Zirconium-89

This review discusses recent advances in light-driven radiochemistry for three key isotopes: fluorine-18, carbon-11, and zirconium-89, and their applications in positron emission tomography (PET). In the case of fluorine-18, the predominant approach involves the use of cyclotron-produced [18F]fluoride or reagents derived thereof. Light serves to activate either the substrate or the fluorine-18 labeled reagent. Advancements in carbon-11 photo-mediated radiochemistry have been leveraged for the radiolabeling of small molecules, achieving various transformations, including 11C-methylation, 11C-carboxylation, 11C-carbonylation, and 11C-cyanation. Contrastingly, zirconium-89 photo-mediated radiochemistry differs from fluorine-18 and carbon-11 approaches. In these cases, light facilitates a postlabeling click reaction, which has proven valuable for the labeling of large biomolecules such as monoclonal antibodies (mAbs). New technological developments, such as the incorporation of photoreactors in commercial radiosynthesizers, illustrate the commitment the field is making in embracing photochemistry. Taken together, these advances in photo-mediated radiochemistry enable radiochemists to apply new retrosynthetic strategies in accessing novel PET radiotracers.

Late-stage guanine C8-H alkylation of nucleosides, nucleotides, and oligonucleotides via photo-mediated Minisci reaction

Chemically modified nucleosi(ti)des and functional oligonucleotides (ONs, including therapeutic oligonucleotides, aptamer, nuclease, etc.) have been identified playing an essential role in the areas of medicinal chemistry, chemical biology, biotechnology, and nanotechnology. Introduction of functional groups into the nucleobases of ONs mostly relies on the laborious de novo chemical synthesis. Due to the importance of nucleosides modification and aforementioned limitations of functionalizing ONs, herein, we describe a highly efficient site-selective alkylation at the C8-position of guanines in guanosine (together with its analogues), GMP, GDP, and GTP, as well as late-stage functionalization of dinucleotides and single-strand ONs (including ssDNA and RNA) through photo-mediated Minisci reaction. Addition of catechol to assist the formation of alkyl radicals via in situ generated boronic acid catechol ester derivatives (BACED) markedly enhances the yields especially for the reaction of less stable primary alkyl radicals, and is the key to success for the post-synthetic alkylation of ONs. This method features excellent chemoselectivity, no necessity for pre-protection, wide range of substrate scope, various free radical precursors, and little strand lesion. Downstream applications in disease treatment and diagnosis, or as biochemical probes to study biological processes after linking with suitable fluorescent compounds are expected.

Late-stage modification of complex drug: Base-controlled Pd-catalyzed regioselective synthesis and bioactivity of arylated osimertinibs

Achieving regioselective synthesis in complex molecules with multiple reactive sites remains a tremendous challenge in synthetic chemistry. Regiodivergent palladium-catalyzed C─H arylation of complex antitumor drug osimertinib with various aryl bromides via the late-stage functionalization strategy was demonstrated here. This reaction displayed a switch in regioselectivity under complete base control. Potassium carbonate (K2CO3) promoted the arylation of acrylamide terminal C(sp2)-H, affording 34 derivatives. Conversely, sodium tert-butoxide (t-BuONa) mediated the aryl C(sp2)-H arylation of the indole C2 position, providing 27 derivatives. The derivative 3r containing a 3-fluorophenyl group at the indole C2 position demonstrated similar inhibition of EGFRT790M/L858R and superior antiproliferative activity in H1975 cells compared to osimertinib, as well as similar antiproliferative activity in A549 cells and antitumor efficacy in xenograft mouse model bearing H1975 cells. This approach provides a "one substrate-multi reactions-multiple products" strategy for the structural modification of complex drug molecules, creating more opportunities for the fast screening of pharmaceutical molecules.

Late-stage modification of bioactive compounds: Improving druggability through efficient molecular editing

Synthetic chemistry plays an indispensable role in drug discovery, contributing to hit compounds identification, lead compounds optimization, candidate drugs preparation, and so on. As Nobel Prize laureate James Black emphasized, "the most fruitful basis for the discovery of a new drug is to start with an old drug"1. Late-stage modification or functionalization of drugs, natural products and bioactive compounds have garnered significant interest due to its ability to introduce diverse elements into bioactive compounds promptly. Such modifications alter the chemical space and physiochemical properties of these compounds, ultimately influencing their potency and druggability. To enrich a toolbox of chemical modification methods for drug discovery, this review focuses on the incorporation of halogen, oxygen, and nitrogen-the ubiquitous elements in pharmacophore components of the marketed drugs-through late-stage modification in recent two decades, and discusses the state and challenges faced in these fields. We also emphasize that increasing cooperation between chemists and pharmacists may be conducive to the rapid discovery of new activities of the functionalized molecules. Ultimately, we hope this review would serve as a valuable resource, facilitating the application of late-stage modification in the construction of novel molecules and inspiring innovative concepts for designing and building new drugs.

Predictive Minisci late stage functionalization with transfer learning

Structural diversification of lead molecules is a key component of drug discovery to explore chemical space. Late-stage functionalizations (LSFs) are versatile methodologies capable of installing functional handles on richly decorated intermediates to deliver numerous diverse products in a single reaction. Predicting the regioselectivity of LSF is still an open challenge in the field. Numerous efforts from chemoinformatics and machine learning (ML) groups have made strides in this area. However, it is arduous to isolate and characterize the multitude of LSF products generated, limiting available data and hindering pure ML approaches. We report the development of an approach that combines a message passing neural network and 13C NMR-based transfer learning to predict the atom-wise probabilities of functionalization for Minisci and P450-based functionalizations. We validated our model both retrospectively and with a series of prospective experiments, showing that it accurately predicts the outcomes of Minisci-type and P450 transformations and outperforms the well-established Fukui-based reactivity indices and other machine learning reactivity-based algorithms.

A decade of USFDA-approved small molecules as anti-inflammatory agents: Recent trends and Commentaries on the "industrial" perspective

Inflammation is the human body's defence process against various pathogens, toxic substances, irradiation, and physically injured cells that have been damaged. Inflammation is characterized by swelling, pain, redness, heat, as well as diminished tissue function. Multiple important inflammatory markers determine the prognosis of inflammatory processes, which include likes of pro-inflammatory cytokines which are controlled by nuclear factor kappa-B (NF-kB), mitogen-activated protein kinase (MAPK), Janus kinase signal transducer and activator of transcription (JAK-STAT) pathway, all of which are activated in response to the stimulation of specific receptors. Besides these, the cyclooxygenase (COX) enzyme family also plays a significant role in inflammation. The current review is kept forth to compile a summary of small molecules-based drugs approved by the USFDA during the study period of 2013-2023. A thorough discussion has also been made to focus on biologics, macromolecules, and small chemical entities approved during this study period and their greener synthetic routes with a brief discussion on the chemical spacing parameters of anti-inflammatory drugs. The compilation is expected to assist the medicinal chemist and the scientist actively engaged in drug discovery and development of anti-inflammatory agents from newer perspectives during the current years.

A Universal, Continuous Assay for SAM-dependent Methyltransferases

Enzyme-catalyzed late-stage functionalization (LSF), such as methylation of drug molecules and lead structures, enables direct access to more potent active pharmaceutical ingredients (API). S-adenosyl-l-methionine-dependent methyltransferases (MTs) can play a key role in the development of new APIs, as they catalyze the chemo- and regioselective methylation of O-, N-, S- and C-atoms, being superior to traditional chemical routes. To identify suitable MTs, we developed a continuous fluorescence-based, high-throughput assay for SAM-dependent methyltransferases, which facilitates screening using E. coli cell lysates. This assay involves two enzymatic steps for the conversion of S-adenosyl-l-homocysteine into H2 S to result in a selective fluorescence readout via reduction of an azidocoumarin sulfide probe. Investigation of two O-MTs and an N-MT confirmed that this assay is suitable for the determination of methyltransferase activity in E. coli cell lysates.

Light-Driven Enantioselective Carbene-Catalyzed Radical-Radical Coupling

An enantioselective carbene-catalyzed radical-radical coupling of acyl imidazoles and racemic Hantzsch esters is disclosed. This method involves the coupling of an N-heterocyclic carbene-derived ketyl radical and a secondary sp3 -carbon radical and allows access to chiral α-aryl aliphatic ketones in moderate-to-good yields and enantioselectivities without any competitive epimerization. The utility of this protocol is highlighted by the late-stage functionalization of various pharmaceutical compounds and is further demonstrated by the transformation of the enantioenriched products to biologically relevant molecules. Computational investigations reveal the N-heterocyclic carbene controls the double-facial selectivity of the ketyl radical and the alkyl radicals, respectively.

Drug Discovery Based on Oxygen and Nitrogen (Non-)Heterocyclic Compounds Developed @LAQV-REQUIMTE/Aveiro

Artur Silva's research group has a long history in the field of medicinal chemistry. The development of new synthetic methods for oxygen (mostly polyphenols, e.g., 2- and 3-styrylchromones, xanthones, flavones) and nitrogen (e.g., pyrazoles, triazoles, acridones, 4-quinolones) heterocyclic compounds in order to be assessed as antioxidant, anti-inflammatory, antidiabetic, and anticancer agents has been the main core work of our research interests. Additionally, the synthesis of steroid-type compounds as anti-Alzheimer drugs as well as of several chromophores as important dyes for cellular imaging broadened our research scope. In this review article, we intend to provide an enlightened appraisal of all the bioactive compounds and their biological properties that were synthesized and studied by our research group in the last two decades.

Synthesis and Insecticidal Activity Study of Azidopyridryl Containing Dichlorolpropene Ether Derivatives

Pyridalyl, as a novel insecticide with an unknown mode of action, has shown excellent control efficacy against lepidopterous larvae and thrips. Previous modifications of this compound have mostly focused on the pyridine moiety, with limited information available about modifications to other parts of pyridalyl. In this paper, we report the synthesis and insecticidal activity of a series of azidopyridryl-containing dichlorolpropene ether derivatives, based on modifications to the middle alkyl chain of pyridalyl. Screening results for insecticidal activity indicate that our synthesized compounds show moderate to high activities at the tested concentrations against P. xylostella. Particularly, compound III-10 exhibits a LC50 value of 0.831 mg L-1, compared to the LC50 value of pyridalyl at 2.021 mg L-1. Furthermore, compound III-10 also displays a relatively broad insecticidal spectrum against Lepidoptera pests M. separata, C. suppressalis, O. nubilalis, and C. medinalis. Finally, in field trials, III-10 demonstrates better control efficiency against Chilo suppressalis compared to pyridalyl. Overall, our findings suggest that the modification of the middle alkyl chain of pyridalyl may be a promising approach for developing insecticides with improved efficacy.

Carbon-Carbon Bond Cleavage for Late-Stage Functionalization

Late-stage functionalization (LSF) introduces functional group or structural modification at the final stage of the synthesis of natural products, drugs, and complex compounds. It is anticipated that late-stage functionalization would improve drug discovery's effectiveness and efficiency and hasten the creation of various chemical libraries. Consequently, late-stage functionalization of natural products is a productive technique to produce natural product derivatives, which significantly impacts chemical biology and drug development. Carbon-carbon bonds make up the fundamental framework of organic molecules. Compared with the carbon-carbon bond construction, the carbon-carbon bond activation can directly enable molecular editing (deletion, insertion, or modification of atoms or groups of atoms) and provide a more efficient and accurate synthetic strategy. However, the efficient and selective activation of unstrained carbon-carbon bonds is still one of the most challenging projects in organic synthesis. This review encompasses the strategies employed in recent years for carbon-carbon bond cleavage by explicitly focusing on their applicability in late-stage functionalization. This review expands the current discourse on carbon-carbon bond cleavage in late-stage functionalization reactions by providing a comprehensive overview of the selective cleavage of various types of carbon-carbon bonds. This includes C-C(sp), C-C(sp2), and C-C(sp3) single bonds; carbon-carbon double bonds; and carbon-carbon triple bonds, with a focus on catalysis by transition metals or organocatalysts. Additionally, specific topics, such as ring-opening processes involving carbon-carbon bond cleavage in three-, four-, five-, and six-membered rings, are discussed, and exemplar applications of these techniques are showcased in the context of complex bioactive molecules or drug discovery. This review aims to shed light on recent advancements in the field and propose potential avenues for future research in the realm of late-stage carbon-carbon bond functionalization.

Electronically flexible PYA ligands for efficient palladium-catalyzed α-arylation of ketones

Palladium-catalyzed cross-coupling chemistry and in particular ketone α-arylation has been relying on a rather narrow range of supporting ligands with almost no alternatives to phosphines and N-heterocyclic carbenes. Here we introduce a class of well-defined palladium(II) complexes supported by N,N'-chelating and electronically flexible pyridylidene amide (PYA)-pyridyl ligands as catalysts for efficient α-arylation of ketones. Steric and electronic variations of the N,N'-bidentate ligand indicate that the introduction of an ortho-methyl group on the pyridinum heterocycle of the PYA ligand enhances the arylation rate and prevents catalyst deactivation, reaching turnover numbers up to 7300 and turnover frequencies of almost 10 000 h-1, which is similar to that of the best phosphine complexes known to date. Introducing a shielding xylyl substituent accelerates catalysis further, however at the expense of lower selectivity towards arylated ketones. Substrate scope investigations revealed that both electron-rich and -poor aryl bromides as well as a broad range of electronically and sterically modified ketones are efficiently converted, including aliphatic ketones. Mechanistic investigations using Hammett and Eyring analyses indicated that both, oxidative addition and reductive elimination are relatively fast, presumably as a consequence of the electronic flexibility of the PYA ligand, while enolate coordination was identified as the turnover-limiting step.

Ambient-Temperature, Metal-Free, CDI-Mediated Ex-Situ Conversion of Acids to Amides: A Useful Late-Stage Strategy

An efficient ex-situ method for the amidation of carboxylic acids mediated by CDI has been disclosed herewith. This metal-free strategy is performed at ambient temperature and can be applied effectively for late-stage modification of amino acids and APIs.

C3-Functionalization of indoles with α-heteroaryl-substituted methyl alcohols

The transition metal-free Cs2CO3/Oxone®-mediated C3-alkylation of indoles proceeds in moderate to high yields with a variety of C4-C7 functionalized indoles and is applicable to 2-, 3- and 4-hydroxymethyl pyridines and related electron-deficient heterocycles, permitting novel late-stage drug functionalizations. Preliminary mechanistic studies support a hydrogen autotransfer-type chain process starting with an initial oxidation of the alcohol to the corresponding aldehyde, followed by a subsequent condensation onto indole and reduction/hydride delivery from another equivalent of the primary alcohol.

Electrochemical Late-Stage Functionalization

Late-stage functionalization (LSF) constitutes a powerful strategy for the assembly or diversification of novel molecular entities with improved physicochemical or biological activities. LSF can thus greatly accelerate the development of medicinally relevant compounds, crop protecting agents, and functional materials. Electrochemical molecular synthesis has emerged as an environmentally friendly platform for the transformation of organic compounds. Over the past decade, electrochemical late-stage functionalization (eLSF) has gained major momentum, which is summarized herein up to February 2023.

Divergent access to 5,6,7-perifused cycles

Nitrogen-containing heterocycles are the key components in many pharmaceuticals and functional materials. In this study, we report a transition metal-catalyzed high-order reaction sequence for synthesizing a structurally unique N-center 5,6,7-perifused cycle (NCPC). The key characteristics include the formation of a seven-membered ring by the 8π electrocyclization of various alkenes and aromatic heterocycles as π-components, in which metal carbene species are generated that further induce the cleavage of the α-C-H or -C-C bond. Specifically, the latter can react with various nucleophilic reagents containing -O, -S, -N, and -C. The stereo-controlled late-stage modification of some complicated pharmaceuticals indicates the versatility of this protocol.

Late-stage Functionalization for Improving Drug-like Molecular Properties

The development of late-stage functionalization (LSF) methodologies, particularly C-H functionalization, has revolutionized the field of organic synthesis. Over the past decade, medicinal chemists have begun to implement LSF strategies into their drug discovery programs, allowing for the drug discovery process to become more efficient. Most reported applications of late-stage C-H functionalization of drugs and drug-like molecules have been to rapidly diversify screening libraries to explore structure-activity relationships. However, there has been a growing trend toward the use of LSF methodologies as an efficient tool for improving drug-like molecular properties of promising drug candidates. In this review, we have comprehensively reviewed recent progress in this emerging area. Particular emphasis is placed on case studies where multiple LSF techniques were implemented to generate a library of novel analogues with improved drug-like properties. We have critically analyzed the current scope of LSF strategies to improve drug-like properties and commented on how we believe LSF can transform drug discovery in the future. Overall, we aim to provide a comprehensive survey of LSF techniques as tools for efficiently improving drug-like molecular properties, anticipating its continued uptake in drug discovery programs.

Synthesis, structure-activity relationship, and biological evaluation of quinolines for development of anticancer agents

Tetrahydro-β-carbolines (THβCs) are a kind of natural alkaloids with multiple pharmaceutical activities. Herein, a focused compound library derived from THβCs was synthesized and their anticancer activities were studied in several cancer cell lines. Among them, three compounds showed considerable anticancer activities with low micromolar to submicromolar IC₅₀ values. The abilities to induce apoptosis and alter mitochondrial membrane potential levels, which are comparable to those of the commercial anticancer drug adriamycin, were confirmed by one representative compound (21) on the B16/F10 cell line. Our preliminary structure-activity relationship studies indicated that alkylamines with suitable lengths are very important for potency improvement.

An update on late-stage functionalization in today's drug discovery

INTRODUCTION

Late-stage functionalization (LSF) allows for the introduction of new chemical groups toward the end of a synthetic sequence, which means new molecules can be rapidly accessed without laborious de novo chemical synthesis. Over the last decade, medicinal chemists have begun to implement LSF strategies into their drug discovery programs, affording benefits such as efficient access to diverse libraries to explore structure-activity relationships and the improvement of physicochemical and pharmacokinetic properties.

AREAS COVERED

An overview of the key advancements in LSF methodology development from 2019 to 2022 and their applicability to drug discovery is provided. In addition, several examples from both academia and industry where LSF methodologies have been applied by medicinal chemists to their drug discovery programs are presented.

EXPERT OPINION

Utilization of LSF by medicinal chemists is on the rise, both in academia and in industry. The maturation of the LSF field to produce methodologies bearing increased regioselectivity, scope, and functional group tolerance is envisaged to narrow the gap between methodology development and medicinal chemistry research. The authors predict that the sheer versatility of these techniques in facilitating challenging chemical transformations of bioactive molecules will continue to increase the efficiency of the drug discovery process.

6-[(2S,3R)-3-(2,4-Difluorophenyl)-3-hydroxy-4-(1H-1,2,4-triazol-1-yl)butan-2-yl]-5-fluoropyrimidine-4-carbaldehyde

Voriconazole (VN) is an antifungal drug indicated for the treatment of several fungal infections. Due to its side effects, some works involving late-stage functionalization of VN have been reported in the literature. Here, we disclose a new VN derivative, the 6-[(2S,3R)-3-(2,4-difluorophenyl)-3-hydroxy-4-(1H-1,2,4-triazol-1-yl)butan-2-yl]-5-fluoropyrimidine-4-carbaldehyde (VN-CHO). This compound results from the photoredox-catalyzed hydroxymethylation of VN, affording a hydroxymethylated derivative (VN-CH2OH), followed by oxidation of the former CH2OH group. VN-CHO was obtained in good yield (70% yield) and its structure was unveiled by 1D (1H and 13C) and 2D (HSQC and HMBC) NMR techniques. The introduction of a formyl group in VN structure creates a very promising site for further functionalization in a molecule which originally does not have many active sites.

The recent advances in cobalt-catalyzed C(sp3)-H functionalization reactions

Over the past decades, reactions involving C-H functionalization have become a hot theme in organic transformations because they have a lot of potential for the streamlined synthesis of complex molecules. C(sp³)-H bonds are present in most organic species. Since organic molecules have massive significance in various aspects of life, the exploitation and functionalization of C(sp³)-H bonds hold enormous importance. In recent years, the first-row transition metal-catalyzed direct and selective functionalization of C-H bonds has emerged as a simple and environmentally friendly synthetic method due to its low cost, unique reactivity profiles and easy availability. Therefore, research advancements are being made to conceive catalytic systems that foster direct C(sp³)-H functionalization under benign reaction conditions. Cobalt-based catalysts offer mild and convenient reaction conditions at a reasonable expense compared to conventional 2^nd and 3^rd-row transition metal catalysts. Consequently, the probing of Co-based catalysts for C(sp³)-H functionalization is one of the hot topics from the outlook of an organic chemist. This review primarily focuses on the literature from 2018 to 2022 and sheds light on the substrate scope, selectivity, benefits and limitations of cobalt catalysts for organic transformations.

Late-stage functionalization of 5-nitrofurans derivatives and their antibacterial activities

Structure modification of drugs is a reliable way to optimize lead compounds, among which the most striking and direct method is late-stage functionalization (LSF). Here, we employed the Cu-catalyzed C-H LSF to modify 5-nitrofuran drugs. A series of modifications have been carried out including hydroxylation, methylation, azidination, cyanation, arylation, etc. Antibacterial activities of all compounds in vitro were measured. The results showed that compound 1 and compound 18 were the most active among all compounds. Meanwhile, the cell cytotoxicity assays of potent compounds 1, 3, 4, 5 & 18 and the parent drug FZD were conducted.

Photoredox-Mediated Deoxygenative Radical Additions of Aromatic Acids to Vinyl Boronic Esters and gem-Diborylalkenes

A new method to access β-keto-gem-diborylalkanes, by direct deoxygenative radical addition of aromatic carboxylic acids to gem-dibortlalkenes, is described. The reaction proceeds under mild photoredox catalysis and involves the photochemical C-O bond activation of aromatic carboxylic acids in the presence of PPh₃ . It generates an acyl radical, which further undergoes an additional reaction with gem-diborylalkenes to form an α-gem-diboryl alkyl radical intermediate, which then reduces to the corresponding anion, which after protonation, affords the β-keto-gem-diborylalkane product. Moreover, the same scenario has been extended to the vinyl boronic esters, for example, gem-(Ar, Bpin)-alkenes, and gem-(Alkyl, Bpin)-alkenes. Importantly, this protocol provides a general platform for the late-stage functionalization of bio-active and drug molecules containing a carboxylic acid group.

Transition-metal-catalyzed C-H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

The last decade has witnessed the emergence of innovative synthetic tools for the synthesis of fluorinated molecules. Among these approaches, the transition-metal-catalyzed functionalization of various scaffolds with a panel of fluorinated groups (XR_F, X = S, Se, O) offered straightforward access to high value-added compounds. This review will highlight the main advances made in the field with the transition-metal-catalyzed functionalization of C(sp²) and C(sp³) centers with SCF₃, SeCF₃, or OCH₂CF₃ groups among others, by C-H bond activation. The scope and limitations of these transformations are discussed in this review.

Manganese-Catalyzed Regioselective C-H Lactonization and Hydroxylation of Fatty Acids with H2O2

Herein, we report the direct selective C-H lactonization of fatty acids (C5-C16), catalyzed by manganese(II) complexes bearing bis-amino-bis-pyridine ligands. The catalyst system uses the environmentally benign hydrogen peroxide as oxidant and exhibits high efficiency (100-200 TON), providing under optimized conditions γ-lactones in 60-90% yields. Remarkably, by changing the reaction conditions, the oxidation of hexanoic acid can be diverted toward formation of δ-caprolactone in up to 67% yield. Furthermore, the possibility of obtaining (ω-1)-hydroxy derivatives from linear C7-C10 acids in up to 48% yields has been demonstrated.

A late-stage functionalization tool: sulfonyl fluoride mediated deoxymethylation of phenols

The late-stage functionalization of drugs and natural products has been identified as a promising approach to accelerate the discovery of new bioactive compounds. Due to the presence of the "Magic Methyl Effect", the direct deoxymethylation of phenolic hydroxyl groups, which are widespread in natural molecules, is a challenging task. A mild and rapid strategy for direct phenol deoxymethylation under metal catalysis using SO₂F₂ is described in this paper, while good functional group tolerance and high chemoselectivity allow this strategy to be one of the powerful tools for LSF. The power of this new platform is showcased through gram-scale and orthogonal experiments.

Use of engineered cytochromes P450 for accelerating drug discovery and development

Numerous steps in drug development, including the generation of authentic metabolites and late-stage functionalization of candidates, necessitate the modification of often complex molecules, such as natural products. While it can be challenging to make the required regio- and stereoselective alterations to a molecule using purely chemical catalysis, enzymes can introduce changes to complex molecules with a high degree of stereo- and regioselectivity. Cytochrome P450 enzymes are biocatalysts of unequalled versatility, capable of regio- and stereoselective functionalization of unactivated CH bonds by monooxygenation. Collectively they catalyze over 60 different biotransformations on structurally and functionally diverse organic molecules, including natural products, drugs, steroids, organic acids and other lipophilic molecules. This catalytic versatility and substrate range makes them likely candidates for application as potential biocatalysts for industrial chemistry. However, several aspects of the P450 catalytic cycle and other characteristics have limited their implementation to date in industry, including: their lability at elevated temperature, in the presence of solvents, and over lengthy incubation times; the typically low efficiency with which they metabolize non-natural substrates; and their lack of specificity for a single metabolic pathway. Protein engineering by rational design or directed evolution provides a way to engineer P450s for industrial use. Here we review the progress made to date toward engineering the properties of P450s, especially eukaryotic forms, for industrial application, and including the recent expansion of their catalytic repertoire to include non-natural reactions.

Progress on structural modification of Tetrandrine with wide range of pharmacological activities

Tetrandrine (Tet), derived from the traditional Chinese herb Fangji, is a class of natural alkaloids with the structure of bisbenzylisoquinoline, which has a wide range of physiological activities and significant pharmacfological effects. However, studies and clinical applications have revealed a series of drawbacks such as its poor water solubility, low bioavailability, and the fact that it can be toxic to humans. The results of many researchers have confirmed that chemical structural modifications and nanocarrier delivery can address the limited application of Tet and improve its efficacy. In this paper, we summarize the anti-tumor efficacy and mechanism of action, anti-inflammatory efficacy and mechanism of action, and clinical applications of Tet, and describe the progress of Tet based on chemical structure modification and nanocarrier delivery, aiming to explore more diverse structures to improve the pharmacological activity of Tet and provide ideas to meet clinical needs.

Zinc-Mediated Transformation of 1,3-Diols to Cyclopropanes for Late-Stage Modification of Natural Products and Medicinal Agents

A method for incorporating cyclopropane motifs into complex molecules has been developed. Herein we report a zinc dust-mediated cross-electrophile coupling reaction of 1,3-dimesylates to synthesize cyclopropanes. 1,3-Dimesylates can be readily accessed from 1,3-diols, a functionality prevalent in many natural products and medicinal agents. The reaction conditions are mild, such that functional groups, including amides, esters, heterocycles, and alkenes, are tolerated. Notably, we have demonstrated late-stage cyclopropanation of statin medicinal agents.

Nickel-catalyzed hydrogenative coupling of nitriles and amines for general amine synthesis

Efficient and general methods for the synthesis of amines remain in high demand in the chemical industry. Among the many known processes, catalytic hydrogenation is a cost-effective and industrially proven reaction and currently used to produce a wide array of such compounds. We report a homogeneous nickel catalyst for hydrogenative cross coupling of a range of aromatic, heteroaromatic, and aliphatic nitriles with primary and secondary amines or ammonia. This general hydrogenation protocol is showcased by straightforward and highly selective synthesis of >230 functionalized and structurally diverse amines including pharmaceutically relevant and chiral products, as well as ¹⁵N-isotope labeling applications.

Diastereo- and Enantioselective Silver-Catalyzed [3+3] Cycloaddition and Kinetic Resolution of Azomethine Imines with Activated Isocyanides

In contrast to the well-established [3+2] cycloaddition reactions, the catalytic enantioselective [3+n] (n≥3) cycloaddition reaction of activated isocyanides for the preparation of six-membered or larger ring systems has remained underdeveloped. Herein, we report the first example of highly diastereo- and enantioselective [3+3] cycloaddition of activated isocyanides with azomethine imines. By employing silver catalysis, a wide range of biologically important bicyclic 1,2,4-triazines were obtained in high yields (up to 99 %) with good to excellent stereoselectivities (up to >20 : 1 dr, 99 % ee). In addition, the same catalytic system could be applied to both the late-stage functionalization of complex bioactive molecules and the kinetic resolution of racemic azomethine imines, further highlighting its versatility and synthetic utility.

C−H Methylation Using Sustainable Approaches

C−H methylation of sp2 and sp3 carbon centers is significant in many biological processes. Methylated drug candidates show unique properties due to the change in solubility, conformation and metabolic activities. Several photo-catalyzed, electrochemical, mechanochemical and metal-free techniques that are widely utilized strategies in medicinal chemistry for methylation of arenes and heteroarenes have been covered in this review.

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.

Taming Shapeshifting Anions: Total Synthesis of Ocellatusone C

Guided by a synthetic design aimed at late-stage diversification, we report the preparation of unusual shapeshifting anions and their subsequent application to the total synthesis of the polyketide natural product ocellatusone C. Site-selective core functionalization of a readily accessible bicyclo[3.3.1]nonane architecture sets the stage for shape-selective side chain installation via a nonfluxional π-allyl Pd-complex derived from a barbaralyl-type anion. Several interesting chemical findings, including substituent-dependent bridged bicycloisomerism and the isolation of a stabilized, 3° carbon-bound Pd-ketone enolate complex, are reported.

Continuous-flow synthesis of alkyl zinc sulfinates for the direct photofunctionalization of heterocycles

A sustainable strategy for the alkylation of heterocycles is presented. The protocol relies on the in situ generation and further in-line use of alkyl zinc sulfinates through a continuous-flow system. The environmentally friendly character of the protocol is assured by the use of a green solvent mixture, the presence of a metal free oxidant and low waste generation.