Visible-light-mediated site-selective C(sp2)-H alkylation of tropones facilitates semi-synthesis of cephafortunoids A and B

The synthesis of functionalized tropones constitutes an underexplored chemical space, primarily due to the intrinsic structural properties of the aromatic nucleus. This predicament has impeded extensive investigation into their potential applications in organic and medicinal chemistry. Here, we report a mild and straightforward visible-light-mediated protocol for the α-site-selective C(sp2)-H alkylation of tropones, employing unactivated secondary amines as alkylating agents. This method yields up to 89% in 48 examples, and is significantly amenable to late-stage functionalization. The utility is showcased by the effective chemical transformation of fortunolide A into cephafortunoids A and B, representing the first synthetic entry to this unique class of C20 Cephalotaxus troponoids. Significantly, this achievement reinforces the chemical feasibility of the newly hypothesized biosynthesis involving direct methylation via radical S-adenosylmethionine (SAM)-dependent methyltransferases.

Dehomologative C-C Borylation of Aldehydes and Alcohols via a Rh-Catalyzed Dehydroformylation-Borylation Relay

The dehomologative conversion of linear or α-methyl aldehydes to vinyl boronates is achieved via a one-pot sequence of rhodium-catalyzed transfer dehydroformylation and transfer borylation of the resulting alkenes. Similarly, allylic or aliphatic alcohols are converted to vinyl boronates through a sequence involving, respectively, rhodium-catalyzed isomerization or transfer dehydrogenation to aldehyde intermediates, followed by dehydroformylation-borylation. The vinyl boronates can be further hydrogenated to alkyl boronates using the same rhodium precatalyst, enabling all five catalytic steps with a single catalyst system.

A unified approach to meta-selective methylation, mono-, di- and trifluoromethylation of arenes

Matched molecular series (MMS) are series of molecules that differ only by a single modification at a specific site. The synthesis of MMS is a desirable strategy in drug discovery campaigns. Small aliphatic motifs, notably methyl, mono-, di- and trifluoromethyl substituents (C1 units), are known to have profound effects on the physiochemical properties and/or potency of drug candidates. In this context, we herein report a unique strategy for achieving direct meta-selective methylation, mono-, di-, and trifluoromethylation from the same parent compound. This approach takes advantage of a highly meta-selective ruthenium(ii)-catalyzed alkylation, followed by a subsequent photocatalyzed protodecarboxylation or silver-mediated fluorodecarboxylation to reveal the (fluoro)methyl moiety. This method enables the late-stage access to MMS in small molecules bearing a variety of orienting groups as well as bio-relevant molecules containing complex functionalities, bypassing the need for de novo synthesis to access individual compounds in a series. Moreover, key physiochemical properties of drug candidates were successfully modulated, highlighting opportunities to accelerate medicinal chemistry programs in a sustainable fashion.

Synergistic LMCT and Ni Catalysis for Methylative Cross-Coupling Using tert-Butanol: Modulating Radical Pathways via Selective Bond Homolysis

Ligand-to-metal charge transfer (LMCT) excitation has emerged as a potent strategy for the selective generation of heteroatom-centered radicals, yet its full potential in modulating open-shell radical pathways remains underexplored. Here, we present a photocatalytic methylative cross-coupling reaction that capitalizes on the synergistic interplay between LMCT and Ni catalysis, enabling the use of tert-butanol as an efficient and benign methylating reagent. The electron-deficient ligand 2,6-ditrifluoromethyl benzoate facilitates Ce(IV)-mediated bond scission of tert-butanol, generating a methyl radical that is subsequently captured by the Ni catalytic cycle to form C-CH3 bonds. Under mild reaction conditions, this strategy affords efficient methylation of sp3 carbons adjacent to carbonyls and sp2 centers, demonstrating broad functional group tolerance and applicability in late-stage functionalization of bioactive molecules. Additionally, trideuteromethylative coupling can be facilely achieved using commercial tert-butanol-d10. This approach circumvents the need for traditional tert-butoxy radical precursors, such as peroxides, while strategically modulating the radical pathway to favor β-scission and suppress unwanted tert-butoxy radical formation in solution. Mechanistic studies reveal that the benzoate ligand plays a crucial role in enabling LMCT excitation and facilitating methyl radical generation, supporting a concerted Ce-OR and β-C-C bond homolysis mechanism, further evidenced by the modulation of regioselectivity in alkoxy radical-mediated β-scission.

Three-Component 1,2-Methylamidation of Alkynes via Coordinating Activation Strategy

The selective functionalization of carbon-carbon triple bonds with methyl groups remains a challenging task. Herein, the successful development of a novel copper-catalyzed three-component 1,2-methylamidation of carbon-carbon triple bond is reported. The readily available coupling partners, picolinamides and alkynes with dicumyl peroxide, serve as both the methyl source and oxidant in this difunctional strategy to access methylated enamides; the substrate scope is broad, demonstrating good functional group compatibility. The synthetic utility of the reaction is also demonstrated through the 1,2-methylamidation of alkynes via late-stage functionalization of substrates bearing biologically relevant molecules.

Iron-Catalyzed Site-Selective Bromination of Benzylic C(sp3)-H Bonds

An iron-catalyzed chemo- and site-selective benzylic C-H bromination has been described. The practical approach uses the C-H substrate as the limiting reagent and commercially available iron(II) bromide at a loading of 1 mol % as the catalyst without the involvement of any extrinsic ligand. The simple and mild reaction can be readily scaled up to gram quantity with good functional group tolerance, offering a convenient route for the late-stage diversification of complex bioactive natural products and pharmaceutical molecules through sequential benzylic C-H bromination.

Precision installation of silyl synthetic handles within arenes by regiocontrolled ruthenium C(sp 2)-H functionalization

The site-selective functionalization of C(sp 2)-H bonds represents a powerful strategy for the synthesis of structurally diverse compounds with broad applicability. Here we report efficient regioselective catalytic methods for the formation of benzyltrimethylsilanes through ruthenium-catalysed C(sp 2)-H silylmethylation. The developed protocols enable selective functionalization at both ortho and meta positions within arenes bearing N-based directing groups. The resulting silylmethyl compounds can undergo diverse transformations, including nucleophilic aromatic substitution, carbonyl addition, olefination and desilylation. Significantly, the regiodivergent installation of silylmethyl synthetic handles allows for the synthesis of the pharmaceutical losmapimod and could further be applied in direct late-stage functionalizations. Mechanistically, an essential role for biscyclometallated ruthenium(II) species has been found, with the formation of intermediate ruthenium(III) species indicated by paramagnetic NMR experiments. These synthetic inventions and mechanistic elucidations signify a transformative step within ruthenium-catalysed C(sp 2)-H functionalization, enabling diverse syntheses and providing a framework for future development.

Regiospecific 2,3-Dialkylindole Synthesis Enabled by Alkylpalladium 1,2-Migration to In Situ Formed Aldimine

2,3-Dialkylindoles play crucial roles in natural products and pharmaceuticals, but the step-efficient and regioselective construction of such privileged structures remains a long-standing challenge. Here, we report a regiospecific non-Fischer indole synthesis through chemoselective 1,2-migratory addition of alkylpalladium to an aldimine intermediate, formed in situ through a palladium hydride-triggered sequential isocyanide and intramolecular olefin insertion. This unprecedented 1,2-migratory addition leads to formal C═C bond cleavage and isocyano carbon insertion between the two sp2 carbons, offering a novel approach to specific 2,3-dialkyl substituted N─H free indoles from readily available alkyl substituted 1-isocyano-2-vinylbenzenes.

Catalytic Reductive Amination and Tandem Amination-Alkylation of Esters Enabled by a Cationic Iridium Complex

Reported herein is a convenient and efficient method for one-pot, catalytic reductive amination, as well as the first multi-component tandem reductive amination-functionalization of bench-stable and readily available common carboxylic esters. This method is based on the cationic [Ir(COD)2]BArF-catalyzed chemoselective hydrosilylation of esters, followed by one-pot acid-mediated amination and nucleophilic addition. The reaction was conducted under mild conditions at a very low catalyst loading (0.1 mol % of Ir), which could be further reduced to 0.001 mol %, as demonstrated by a reaction at a 15 g scale. The method is highly versatile, allowing the use of esters with or without α-protons for the N-mono-alkylation of primary and secondary amines to produce diverse secondary and tertiary amines, as well as α-branched/functionalized amines. The method is highly chemoselective and tolerates a variety of functional groups such as bromo, trifluoromethyl, ester, and cyano groups. The value of the method was demonstrated by the one-step catalytic synthesis of two bio-relevant N-mono-methyl α-amino esters and the antiparkinsonian agent piribedil, as well as by the use of two shorter chain triglycerides as alkylating feedstock.

Non-enzymatic methylcyclization of alkenes

Methyltransferases are a broad class of enzymes that catalyse the transfer of methyl groups onto a wide variety of substrates and functionalities. In their most striking variant, bifunctional methyltransferase-cyclases both transfer a methyl group onto alkenes and induce cyclization (methylcyclization). Although recent years have seen substantial advances in the methylation of alkenes, especially hydromethylation, the reactivity demonstrated by bifunctional methyltransferase-cyclases in nature has yet to be developed into a synthetically viable method. Here we report a silver(I)-mediated electrophilic methylcyclization that rivals selectivities found in enzymes while not being limited by their inherent substrate specificity. Our method benefits from the use of commercial reagents, is applicable to a wide range of substrates, including heterocycles, and affords unique structures that are difficult to access via conventional synthetic methods. Furthermore, computational studies have been utilized to unravel the underlying mechanism and ultimately support a stepwise cationic reaction pathway with a rate-limiting methyltransfer.

Design, synthesis, in-vitro and in-silico studies of novel N-heterocycle based hydrazones as α-glucosidase inhibitors

Diabetes mellitus has dominated the globe as a chronic health condition and has become a major global health concern. The inhibition of the key metabolic enzymes of carbohydrates digestion including α-amylase and α-glucosidase are the promising targets for the treatment of diabetes via delaying glucose absorption. Therefore, nitrogen containing saturated heterocycle (pyrrolidinyl, piperidinyl and N-methylpiperazinyl) based hydrazones derivatives 5-23 were synthesized through two step reactions and evaluated for their anti-diabetic potential. All compounds exhibited potent α-glucosidase inhibitory capability ranging (IC50 = 10.26-47.35 µM), as compared to acarbose (IC50 = 871.40 ± 1.24 µM). Interestingly these derivatives also exhibited significant inhibitory capability against α-amylase with IC50 values in the range 25.81-76.05 µM. Mechanistic study on the most potent compound indicated a competitive type of inhibition with a Ki value of 8.30 ± 0.0076 µM. Molecular docking was performed to predict binding interactions between receptor proteins and moiety. In QSAR analysis, through use of QSARINS different 1D and 2D descriptors were used to generate different models that enabled further identification of structural requirements that contributed to activity. pIC50 values were also predicted by QSAR model. Furthermore, in-silico ADMET and BOILED-egg model analysis showed that all analogues exhibited passive GI absorption, and all showed BBB penetration.

Harnessing the Magic Methyl Effect: Discovery of CLPP-2068 as a Novel HsClpP Activator for the Treatment of Diffuse Large B-Cell Lymphoma

The "magic methyl effect" has facilitated the successful development of numerous pharmaceutical compounds. During the development of HsClpP activators, we found that incorporating methyl groups into the bicyclic imipridone scaffolds significantly enhanced the activator activity at the enzymatic level. Further structure-activity relationship studies led to the identification of a highly promising compound, CLPP-2068, which exhibited an EC50 value of 50.4 nM. Cryo-electron microscopy techniques and computational analyses demonstrated that the introduction of methyl groups facilitated the formation of additional CH-π interactions between CLPP-2068 and HsClpP, thereby lowering the energy barriers during the binding process. Furthermore, additional pharmaceutical analyses indicated that CLPP-2068 exhibited favorable pharmacokinetic properties and effectively mitigated the potential hERG toxicity observed in imipridone-based HsClpP activators. Collectively, CLPP-2068, developed using the magic methylation strategy, holds potential as a therapeutic agent for the treatment of diffuse large B-cell lymphoma, thereby expanding the clinical indications for HsClpP activators.

Catalytic Asymmetric Synthesis and Applications of Stereogenic β'-Methyl Enones and β,β'-Dimethyl Ketones

The "Magic Methyl" effect has received tremendous interest in medicinal chemistry due to the significant pharmacological and physical modification of properties that have been observed upon introducing a methyl group, especially, a stereogenic methyl group into potential chiral drug candidates. The prevalence of stereogenic β-methyl ketone structural motifs in bioactive compounds and natural products has long motivated the development of enantioselective strategies toward their synthesis. Herein, we have rationally designed a Rh-catalyzed asymmetric monohydrogenation of readily-available β'-methylene conjugated enones with high efficiency and remarkable site-selectivity and enantioselectivity control for the practical construction of enantioenriched β'-methyl unsaturated enones that are difficult to access by other methods. Control experiments revealed that the conjugated C=C bond in β'-methylene conjugated enones plays a significant role in enhancing the reactivity of monohydrogenation. This methodology is applicable for the preparation of chiral β,β'-dimethyl ketones through consecutive double asymmetric hydrogenation of β,β'-dimethylene ketones. Detailed mechanistic investigation and DFT studies further provided strong support for a unique processive catalysis pathway for double asymmetric hydrogenation. The synthetic utilities have been demonstrated in the concise synthesis of several key intermediates for bioactive molecules, asymmetric total synthesis of natural products (S)-(+)-ar-Turmerone and (S)-(+)-dihydro-ar-Turmerone, and two C2-symmetric chiral spirocyclic diol frameworks.

Visible-Light-Induced C(sp3)-H Activation for Minisci Alkylation of Pyrimidines Using CHCl3 as Radical Source and Oxidant

A highly efficient Minisci reaction of pyrimidines with alkyl radical generated from visible-light-induced activation of simple C(sp3)-H feedstocks such as (cyclo)alkanes, ethers, alcohols, esters, and amides is reported. A mechanistic study revealed that alkyl radical was generated via hydrogen atom transfer (HAT) of C(sp3)-H with dichloromethyl radical (·CHCl2), which was generated by photoreduction of chloroform.

Cyclic Sulfoximines as Methyl and Perdeuteromethyl Transfer Agents and Their Applications in Photoredox Catalysis

Benzo[1,3,2]dithiazole-1,1,3-trioxides are bench-stable and easy-to-use reagents. In photoredox catalysis, they generate methyl and perdeuteromethyl radicals which can add to a variety of radical acceptors, including olefins, acrylamides, quinoxalinones, isocyanides, enol silanes, and N-Ts acrylamide. As byproduct, a salt is formed which can be regenerated to the original methylating agent. Flow chemistry provides an option for reaction scale-up further underscoring the synthetic usefulness of these methylation reagents. Mechanistic investigations suggest a single-electron transfer (SET) pathway induced by photoredox catalysis.

Photoredox-Catalyzed C-H Methylation of N-Heteroarenes Enabled by N,N-Dimethylethanolamine

A visible-light-driven radical C-H methylation of N-heteroarenes that is efficient and additive- and catalyst-free and employs readily available N,N-dimethylethanolamine as the methyl source has been developed. The transformation offers the benefits of broad substrate scope, mild reaction conditions, and operational simplicity. A photoactive electron donor-acceptor (EDA) complex between N-heteroarenes and N,N-dimethylethanolamine is essential for this transformation, as revealed by mechanistic investigations.

Pnictogen and Chalcogen Salts as Alkylating Agents

Alkylation reactions and their products are considered crucial in various contexts. Synthetically, the alkylation of a nucleophile is usually promoted using hazardous alkyl halides. Here, we aim to highlight the potential of pnictogen (ammonium or phosphonium) and chalcogen salts (sulfonium, selenonium, and telluronium) to function as alkylating agents. These compounds can be considered as non-volatile electrophilic alkyl reservoirs. We will center our discussion on the strategies developed in recent years to expand the synthetic utility of these salts in terms of transferable alkyl groups, substrate scope, and product selectivity.

Diastereoselective Hydrodifluoromethylation of Alkenyl N-Heterocycles via Photocatalytic Radical-Polar Crossover

A diastereoselective hydrodifluoromethylation of N-heteroaryl alkenes was successfully established. This method was applicable to an array of N-heteroaryl substrates with both cyclic and acyclic alkenes while displaying tolerance to a variety of functional groups. The conditions were also expanded to obtain hydrotrifluoromethylated products with similar results. Initial mechanistic studies suggest that the final protonation step is accessed through a radical-polar crossover process.

Sustainable C-H Methylation Employing Dimethyl Carbonate

The use of CO2 and CO2-derived chemicals offers society sustainable and biocompatible chemistry for a variety of applications, ranging from materials to medicines. In this context, dimethyl carbonate (DMC) stands out owing to its low toxicity, high biodegradability, tunable reactivity, and sustainable production. Further, the ability of DMC to act as an ambient electrophile at varied temperatures and reaction conditions in order to produce methoxycarbonylated (via BAC2) and methylated products (via BAL2) is very promising. While the methylation of hetero-H (N-, O-, and S-methylation) with DMC is established and well-reviewed, the C-H methylation reaction with DMC is limited, and there is no specific literature detailing the C-methylation reaction using DMC, creating new opportunities as well as challenges in the same domain. In this context, the present perspective focuses on the new breakthroughs, recent advances, and trends in C-H methylation reactions employing DMC. A critical analysis of the mechanistic course of reactions under each category was undertaken. We believe this timely perspective will offer an in-depth analysis of existing literature with critical remarks, which will certainly inspire fellow researchers across disciplines to understand and pursue cutting-edge research in the area of C-H methylation (alkylation) using DMC and related organic carbonates.

Ru(II)-Catalyzed Sustainable C-H Methylation of Indolines with Organoboranes in Ethanol

A sustainable protocol for Ru(II)-catalyzed regioselective C(sp2)-H methylation of indolines in the presence of ethanol has been explored. A wide array of substituted indolines were successfully methylated via the developed protocol with good to excellent yields. Deuterium labeling experiments suggested the reversible nature of the C-H activation step. Kinetic isotope effect studies revealed that C-H activation might be the rate-determining step. Gram scale reaction and post-transformation reactions of the methylated product demonstrated the potential of the developed protocol.

Discovery of a Potent, Orally Active, and Long-Lasting P2X7 Receptor Antagonist as a Preclinical Candidate for Delaying the Progression of Chronic Kidney Disease

Chronic kidney disease (CKD) is a condition characterized by functional deterioration with sustained inflammation and progressive fibrosis of the kidneys affecting over 800 million people worldwide. The P2X7 receptor (P2X7R) plays a key role in CKD progression. Our previous P2X7R antagonists demonstrated good efficacy for treating kidney injury but were limited by low oral exposure and short half-life, restricting their application. This study reports the optimization of P2X7R antagonists for better oral pharmacokinetics. The candidate compound 13a with the respective IC50 of 34.86 and 25.28 nM against human and murine P2X7R, administered orally at 10 mg/kg in mice, exhibits a remarkably long half-life of 161.64 h, with a high exposure of 1,163,980.55 μg·h/L. Oral administration of 13a (0.3 or 1.0 mg/kg, twice weekly) significantly reduced renal injury and fibrosis in unilateral ureteral obstruction and adenine diet-induced mice models, highlighting its potential for delaying the progression of CKD.

A Modified Arbuzov-Michalis Reaction for Selective Alkylation of Nucleophiles

The alkylation of nucleophiles is among the most fundamental and well-developed transformations in chemistry. However, to achieve selective alkylation of complex substrates remains a nontrivial task. We report herein a general and selective alkylation method without using strong acids, bases, or metals. In this method, the readily available phosphinites/phosphites, in combination with ethyl acrylate, function as effective alkylating agents. Various nucleophilic groups, including alcohols, phenols, carboxylic acids, imides, and thiols can be alkylated. This method can be applied in the late-stage alkylation of natural products and pharmaceutical agents, achieving chemo- and site-selective modification of complex substrates. Experimental studies indicate the relative reactivity of a nucleophile depends on its acidity and its steric environment. Mechanistic studies suggest the reaction pathway resembles that of the Arbuzov-Michalis reaction.

Electrochemical Skeletal Indole Editing via Nitrogen Atom Insertion by Sustainable Oxygen Reduction Reaction

Skeletal molecular editing gained considerable recent momentum and emerged as a uniquely powerful tool for late-stage diversifications. Thus far, superstoichiometric amounts of costly hypervalent iodine(III) reagents were largely required for skeletal indole editing. In contrast, we herein show that electricity enables sustainable nitrogen atom insertion reactions to give bio-relevant quinazoline scaffolds without stoichiometric chemical redox-waste product. The transition metal-free electro-editing was enabled by the oxygen reduction reaction (ORR) and proved robust on scale, while tolerating a variety of valuable functional groups.

Silane-mediated, facile C-H and N-H methylation using formaldehyde

The use of (para)-formaldehyde for the methylation/alkylation of C(sp2)-H and N-H bonds, utilizing a combination of silane and hexafluoroisopropanol (HFIP) as activators, is reported. Overcoming the complexity of C(sp2)-H methylation on aryl and indole substrates, the process utilizes a Friedel-Crafts alkylation, followed by silane as a hydride donor, under a mild acidic medium. The method has been employed for the synthesis of the antifungal drug butenafine and a derivative of the non-steroidal anti-inflammatory drug (NSAID) flurbiprofen.

13-Methylpalmatine improves myocardial infarction injury by inhibiting CHOP-mediated cross-talk between endoplasmic reticulum and mitochondria

Myocardial infarction (MI) is a leading cause of morbidity and mortality worldwide, and endoplasmic reticulum stress (ERS) and mitochondrial Ca2+ overload have been involved in apoptotic cardiomyocyte death during MI. 13-Methylpalmatine (13-Me-PLT) is a natural isoquinoline alkaloid isolated from Coptis chinensis and has not been systematically studied for their potential pharmacological effects in cardiovascular diseases. We conducted the present study to elucidate whether 13-Me-PLT modulates MI pathology in animal MI and cellular hypoxic models, employing state-of-the-art molecular techniques. The results demonstrated that 13-Me-PLT preserved post-ischemic cardiac function and alleviated cardiomyocyte apoptosis. 13-Me-PLT decreased ERS and the communication between ER and mitochondria, which serves as a protective mechanism against mitochondrial Ca2+ overload and structural and functional injuries to mitochondria. Our data revealed mitigating mitochondrial Ca2+ overload and apoptosis by inhibiting CHOP-mediated Ca2+ transfer between inositol 1,4,5-trisphosphate receptor (IP3R) in ER and VDAC1 in mitochondria as an underlying mechanism for 13-Me-PLT action. Furthermore, 13-Me-PLT produced superior effects in alleviating cardiac dysfunction and apoptosis post-MI to diltiazem and palmatine. Collectively, our research suggests that the CHOP/IP3R/VDAC1 signaling pathway mediates ER-mitochondrial Ca2+ transfer and 13-Me-PLT activates this axis to maintain cellular and organellar Ca2+ homeostasis, protecting against ischemic myocardial injury. These findings may offer an opportunity to develop new agents for the therapy of ischemic heart disease.

Catalytic undirected methylation of unactivated C(sp3)-H bonds suitable for complex molecules

In pharmaceutical discovery, the "magic methyl" effect describes a substantial improvement in the pharmacological properties of a drug candidate with the incorporation of methyl groups. Therefore, to expedite the synthesis of methylated drug analogs, late-stage, undirected methylations of C(sp3)-H bonds in complex molecules would be valuable. However, current methods for site-selective methylations are limited to activated C(sp3)-H bonds. Here we describe a site-selective, undirected methylation of unactivated C(sp3)-H bonds, enabled by photochemically activated peroxides and a nickel(II) complex whose turnover is enhanced by an ancillary ligand. The methodology displays compatibility with a wide range of functional groups and a high selectivity for tertiary C-H bonds, making it suitable for the late-stage methylation of complex organic compounds that contain multiple alkyl C-H bonds, such as terpene natural products, peptides, and active pharmaceutical ingredients. Overall, this method provides a synthetic tool to explore the "magic methyl" effect in drug discovery.

Leveraging long-lived arenium ions in superacid for meta-selective methylation

Electrophilic aromatic substitution is one of the most mechanistically studied reactions in organic chemistry. However, precluded by innate substituent effects, the access to certain substitution patterns remains elusive. While selective C-H alkylation of biorelevant molecules is eagerly awaited, especially for the insertion of a methyl group whose magic effect can boost lead molecules potency, one of the most obvious strategies would rely on electrophilic aromatic substitution. Yet, the historical Friedel-Crafts methylation remains to date poorly selective and limited to activated simple aromatics. Here, we report the development of a selective electrophilic methylation enabling the direct access to highly desirable 1,3-disubstituted arenes. This study demonstrates that this reaction is driven by the generation of long-lived arenium intermediates generated by protonation in superacid and can be applied to a large variety of functionalized (hetero)aromatics going from standard building blocks to active pharmaceutical ingredients.

The malonyl/acetyl-transferase from murine fatty acid synthase is a promiscuous engineering tool for editing polyketide scaffolds

Modular polyketide synthases (PKSs) play a vital role in the biosynthesis of complex natural products with pharmaceutically relevant properties. Their modular architecture makes them an attractive target for engineering to produce platform chemicals and drugs. In this study, we demonstrate that the promiscuous malonyl/acetyl-transferase domain (MAT) from murine fatty acid synthase serves as a highly versatile tool for the production of polyketide analogs. We evaluate the relevance of the MAT domain using three modular PKSs; the short trimodular venemycin synthase (VEMS), as well as modules of the PKSs deoxyerythronolide B synthase (DEBS) and pikromycin synthase (PIKS) responsible for the production of the antibiotic precursors erythromycin and pikromycin. To assess the performance of the MAT-swapped PKSs, we analyze the protein quality and run engineered polyketide syntheses in vitro. Our experiments include the chemoenzymatic synthesis of fluorinated macrolactones. Our study showcases MAT-based reprogramming of polyketide biosynthesis as a facile option for the regioselective editing of substituents decorating the polyketide scaffold.

Strategies for Using Quaternary Ammonium Salts as Alternative Reagents in Alkylations

Alkylation reactions are pivotal in organic chemistry, with wide-ranging utilization across various fields of applied synthetic chemistry. However, conventional reagents employed in alkylations often pose substantial health and exposure risks. Quaternary ammonium salts (QAS) present a promising alternative for these transformations offering significantly reduced hazards as they are non-cancerogenic, non-mutagenic, non-flammable, and non-corrosive. Despite their potential, their use in direct organic transformations remains relatively unexplored. This review outlines strategies for utilizing QAS as alternative reagents in alkylation reactions, providing researchers with safer approaches to chemical synthesis.

Modular Approach to Highly Substituted 3-Methylpyridones

A method has been developed for the rapid synthesis of highly substituted 3-methylpyridones via the condensation of Baylis-Hillman amines and ketones under benzoic acid catalysis. The process features readily available starting materials, broad substrate scope, high functional group tolerance, excellent regioselectivity, and gram-scale synthesis. We envision that this on-demand construction of 3-methylpyridones will provide exciting opportunities in biological research, therapeutics, and material sciences.

Molecular Motors' Magic Methyl and Its Pivotal Influence on Rotation

Molecular motors have found a wide range of applications, powering a transition from molecules to dynamic molecular systems for which their motion must be precisely tuned. To achieve this adjustment, strategies involving laborious changes in their design are often used. Herein, we show that control over a single methyl group allows a drastic change in rotational properties. In this regard, we present the straightforward asymmetric synthesis of β-methylated first-generation overcrowded-alkene-based molecular motors. Both enantiomers of the new motors were prepared in good yields and high enantiopurities, and these motors were thoroughly studied by variable-temperature nuclear magnetic resonance (VT-NMR), ultraviolet-visible (UV-vis), and circular dichroism (CD) spectroscopy, showing a crucial influence of the methylation pattern on the rotational behavior of the motors. Starting from a common chiral precursor, we demonstrate that subsequent methylation can drastically reduce the speed of the motor and reverse the direction of the rotation. We show for the first time that complete unidirectionality can be achieved even when the energy difference between the stable and metastable states is small, resulting in the coexistence of both states under ambient conditions without hampering the energy ratcheting process. This discovery opens the way for the design of more advanced first-generation motors.

A Guide for Mono-Selective N-Methylation, N-Ethylation, and N-n-Propylation of Primary Amines, Amides, and Sulfonamides and Their Applicability in Late-Stage Modification

This review provides a comprehensive overview of mono-alkylation methodologies targeting crucial nitrogen moieties - amines, amides, and sulfonamides - found in organic building blocks and pharmaceuticals. Emphasizing the intersection of chemical precision with drug discovery, the central challenge addressed is achieving one-pot mono-selective short-chain N-alkylations (methylations, ethylations, and n-propylations), preventing undesired overalkylation. Additionally, sustainable, safe, and benign alternatives to traditional alkylating agents, including alcohols, carbon dioxide, carboxylic acids, nitriles, alkyl phosphates, quaternary ammonium salts, and alkyl carbonates, are explored. This review, categorized by the nature of the alkylating agent, aids researchers in selecting suitable methods for mono-selective N-alkylation.

Harnessing alcohols as sustainable reagents for late-stage functionalisation: synthesis of drugs and bio-inspired compounds

Alcohol is ubiquitous with unparalleled structural diversity and thus has wide applications as a native functional group in organic synthesis. It is highly prevalent among biomolecules and offers promising opportunities for the development of chemical libraries. Over the last decade, alcohol has been extensively used as an environmentally friendly chemical for numerous organic transformations. In this review, we collectively discuss the utilisation of alcohol from 2015 to 2023 in various organic transformations and their application toward intermediates of drugs, drug derivatives and natural product-like molecules. Notable features discussed are as follows: (i) sustainable approaches for C-X alkylation (X = C, N, or O) including O-phosphorylation of alcohols, (ii) newer strategies using methanol as a methylating reagent, (iii) allylation of alkenes and alkynes including allylic trifluoromethylations, (iv) alkenylation of N-heterocycles, ketones, sulfones, and ylides towards the synthesis of drug-like molecules, (v) cyclisation and annulation to pharmaceutically active molecules, and (vi) coupling of alcohols with aryl halides or triflates, aryl cyanide and olefins to access drug-like molecules. We summarise the synthesis of over 100 drugs via several approaches, where alcohol was used as one of the potential coupling partners. Additionally, a library of molecules consisting over 60 fatty acids or steroid motifs is documented for late-stage functionalisation including the challenges and opportunities for harnessing alcohols as renewable resources.

Electro-oxidative Methylation of 2-Isocyanobiaryls Using N,N-dimethylformamide (DMF) as Carbon Source: Synthesis of 6-Methylphenanthridines

A benign electrochemical method to access 6-methylphenanthridines from 2-isocyanobiaryls using N,N-dimethylformamide (DMF) as a methyl source is reported. The protocol operates at ambient temperature without the need for harmful methylating reagents. Mechanistic studies suggested that DMF delivered a methylene synthon, followed by reduction at the cathode and tautomerization. The method offers environmental benefits by avoiding metal-based reagents and harsh conditions.

Methyl-Containing Pharmaceuticals

This Special Issue, which focused on methyl-containing pharmaceuticals, collected different papers and reviews on this topic [...].

Triplet Energy Transfer Mechanism in Copper Photocatalytic N- and O-Methylation

Methylation reactions are chemically simple but challenging to perform under mild and non-toxic conditions. A photochemical energy transfer strategy was merged with copper catalysis to enable fast reaction times of minutes and broad applicability to N-heterocycles, (hetero-)aromatic carboxylic acids, and drug-like molecules in high yields and good functional group tolerance. Detailed mechanistic investigations, using kinetic analysis, aprotic MS, UV/Vis, and luminescence quenching experiments revealed a triplet-triplet energy transfer mechanism between hypervalent iodine(III) reagents and readily available photosensitizers.

Redefining the Synthetic Logic of Medicinal Chemistry. Photoredox-Catalyzed Reactions as a General Tool for Aliphatic Core Functionalization

C(sp3)-rich aliphatic motifs in drug molecules are strongly associated with clinical success. Historically, the availability of compound libraries based on C(sp3)-rich cores has been limited due to the challenging direct functionalization of aliphatic rings. Instead, most small molecule drug-like libraries are diversified around central aromatic rings. Herein, we present a general approach to the synthesis of diversified libraries featuring aliphatic core rings via photoredox catalysis under mild conditions.

4-(Azolyl)-Benzamidines as a Novel Chemotype for ASIC1a Inhibitors

Acid-sensing ion channels (ASICs) play a key role in the perception and response to extracellular acidification changes. These proton-gated cation channels are critical for neuronal functions, like learning and memory, fear, mechanosensation and internal adjustments like synaptic plasticity. Moreover, they play a key role in neuronal degeneration, ischemic neuronal injury, seizure termination, pain-sensing, etc. Functional ASICs are homo or heterotrimers formed with (ASIC1-ASIC3) homologous subunits. ASIC1a, a major ASIC isoform in the central nervous system (CNS), possesses an acidic pocket in the extracellular region, which is a key regulator of channel gating. Growing data suggest that ASIC1a channels are a potential therapeutic target for treating a variety of neurological disorders, including stroke, epilepsy and pain. Many studies were aimed at identifying allosteric modulators of ASIC channels. However, the regulation of ASICs remains poorly understood. Using all available crystal structures, which correspond to different functional states of ASIC1, and a molecular dynamics simulation (MD) protocol, we analyzed the process of channel inactivation. Then we applied a molecular docking procedure to predict the protein conformation suitable for the amiloride binding. To confirm the effect of its sole active blocker against the ASIC1 state transition route we studied the complex with another MD simulation run. Further experiments evaluated various compounds in the Enamine library that emerge with a detectable ASIC inhibitory activity. We performed a detailed analysis of the structural basis of ASIC1a inhibition by amiloride, using a combination of in silico approaches to visualize its interaction with the ion pore in the open state. An artificial activation (otherwise, expansion of the central pore) causes a complex modification of the channel structure, namely its transmembrane domain. The output protein conformations were used as a set of docking models, suitable for a high-throughput virtual screening of the Enamine chemical library. The outcome of the virtual screening was confirmed by electrophysiological assays with the best results shown for three hit compounds.

Mechanistic Insights into the Origins of Selectivity in a Cu-Catalyzed C-H Amidation Reaction

The catalytic transformation of C-H to C-N bonds offers rapid access to fine chemicals and high-performance materials, but achieving high selectivity from undirected aminations of unactivated C(sp3)-H bonds remains an outstanding challenge. We report the origins of the reactivity and selectivity of a Cu-catalyzed C-H amidation of simple alkanes. Using a combination of experimental and computational mechanistic studies and energy decomposition techniques, we uncover a switch in mechanism from inner-sphere to outer-sphere coupling between alkyl radicals and the active Cu(II) catalyst with increasing substitution of the alkyl radical. The combination of computational predictions and detailed experimental validation shows that simultaneous minimization of both Cu-C covalency and alkyl radical size increases the rate of reductive elimination and that both strongly electron-donating and electron-withdrawing substituents on the catalyst accelerate the selectivity-determining C-N bond formation process as a result of a change in mechanism. These findings offer design principles for the development of improved catalyst scaffolds for radical C-H functionalization reactions.

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.

Non-enzymatic synthesis of C-methylated fluostatins: discovery and reaction mechanism

Two C-methylated fluostatins (FSTs) B3 (1) and B4 (2) were synthesized from flavin-mediated nonenzymatic epoxide ring-opening reactions of FST C. The structures of 1 and 2 were elucidated by HRESIMS, NMR, and ECD spectroscopic analyses. A subsequent 13C labeling study demonstrated that the C-methyl groups of 1 and 2 were derived from DMSO and enabled the mechanistic proposal of a nonenzymatic C-methylation.

Visible-light photocatalyzed C-N bond activation of tertiary amines: a three-component approach to synthesize quinazolines

A metal-free three-component approach has been developed to prepare 2,4-disubstituted quinazolines from o-acylanilines, trialkylamines and ammonium chloride under visible-light using eosin Y as the photocatalyst. The notable features of this work include (i) the use of tertiary amines as an alkyl synthon and triethanolamine as a C2-OH synthon; (ii) good functional group tolerance with 52%-98% yields; (iii) proof of concept with o-amino benzaldehyde as a substrate to deliver 2-methyl quinazoline 3pa; and (iv) gram-scale synthesis of compounds 3ga, 3ja and 3ma. A reductive quenching mechanism was proposed based on the control studies and redox potential values.

Ruthenium(II)-Catalyzed Hydrogenation and Tandem (De)Hydrogenation via Metal-Ligand Cooperation: Base- and Solvent-Assisted Switchable Selectivity

A versatile, selective, solvent (methanol vs ethanol)- and base (potassium vs lithium carbonate)-assisted switchable synthesis of saturated ketone and α-methyl saturated ketone from α,β-unsaturated ketone is developed. Mechanistic aspects, evaluated from spectroscopic studies, in situ monitoring of the reaction progress, control studies, and labeling studies, further indicate the involvement of a tandem dehydrogenation-condensation-hydrogenation sequence in the reaction, in which the interconvertible coordination mode (imino N → Ru and amido N-Ru) of coordinated imidazole with Ru(II)-para-cymene is crucial, without which the efficiency and selectivity of the catalyst are completely lost. The catalyst demonstrates good efficiency, selectivity, and functional group tolerance and displays a broad scope (69 examples) for monomethylation and hydrogenation of unsaturated chalcones, double methylation of ketones, and N-methylation of amines.

Regioselective Thiol-yne Reaction of Thiol with ((Methyl-d3)sulfonyl)ethyne: Synthesis of (2-((Methyl-d3)sulfonyl)vinyl)sulfides

Herein, we have developed a new method for the synthesis of ((methyl-d3)sulfonyl)ethyne, which is cost-effective and environmentally friendly and can be synthesized at the gram level. As an ideal thiol-yne reagent, it can be reacted with various types of thiols to afford (Z)- and (E)-type vinyl sulfides under different conditions with high selectivity. In addition, it can complete the conformational transition from Z- to E-type products under suitable conditions, and can also carry out further derivatization smoothly. The deuterium content of all products was greater than 99%. The preliminary mechanistic studies support the visible light-mediated radical course, and herein provide a novel and efficient synthetic strategy for the direct introduction of deuterated methyl groups, enriching the methods for the construction of C-S bond-containing compounds.

Photo-Induced C-H Methylation Reactions

Direct C-H methylation is a highly valuable approach for introducing methyl groups into organic molecules, particularly in pharmaceutical chemistry. Among the various methodologies available, photo-induced methylation stands out as an exceptional choice due to its mild reaction conditions, energy efficiency, and compatibility with functional groups. This article offers a comprehensive review of photochemical strategies employed for the direct and selective methylation of C(sp3 )-H, C(sp2 )-H, and C(sp)-H bonds in various organic molecules. The discussed methodologies encompass transition-metal-based photocatalysis, organophotocatalysis, as well as other metal-free approaches, including electron donor-acceptor (EDA)-enabled transformations. Importantly, a wide range of easily accessible agents such as tert-butyl peroxide, methanol, DMSO, methyl tert-butyl ether, TsOMe, N-(acetoxy)phthalimide, acetic acid, methyl halides, and even methane can serve as effective methylating reagents for modifying diverse targets. These advancements in photochemical C-H methylation are anticipated to drive further progress in the fields of organic synthesis, photocatalysis, and pharmaceutical development, opening up exciting avenues for creating novel organic molecules and discovering new drug compounds.

Late-Stage C-H Activation of Drug (Derivative) Molecules with Pd(ll) Catalysis

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.

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.

Organo-photoredox-Catalyzed Selective Mono- and Bis-C-H Alkylation of Electron-Rich (Hetero)Arenes

Herein, we disclose a simple strategy for the C-H alkylation of electron-rich (hetero)arenes with alkyl bromides employing visible-light-mediated organo-photocatalytic SET processes. The generality of this method has been evidenced by the inclusion of a variety of alkyl radicals (α-alkyl-carbonyl, benzyl, cyanomethyl) as well as diverse biologically active electron-rich arenes and (hetero)arenes under mild conditions. The extent of alkylation with alkyl bromides was found to be controlled by introducing Zn(OAc)2 as a bromide scavenger, ensuring the blocking of potential bromo-arene byproduct formation under photoredox conditions. In addition, a sequential C-H alkylation strategy for selective bis-alkylation has also been developed via chronological incorporation of different alkyl radical precursors in one pot quite efficiently.

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.