Bioinspired design of a robust d 3-methylating agent

Photoinduced Nickel-Mediated Radical Coupling Reaction of Sodium Sulfinates with N-Hydroxyphthalimide Esters

Aryl methyl sulfones represent a privileged structural motif in modern drug discovery due to their diverse biological activities and metabolic stability. However, conventional synthetic approaches for these valuable compounds typically necessitate harsh reaction conditions, including elevated temperatures, strong oxidants, or air-sensitive reagents, which significantly limit their applicability in pharmaceutical synthesis. Herein, we present a novel and efficient strategy for the synthesis of aryl methyl/trideuterated methyl sulfones through nickel-mediated radical coupling, which involves the synergistic combination of methyl radicals generated from N-hydroxyphthalimide (NHP) esters and sulfonyl radicals derived from sodium sulfinates. This protocol establishes a versatile platform for the efficient synthesis of diverse aromatic methyl sulfones and their trideuterated analogues under mild reaction conditions, demonstrating good functional group compatibility and a broad substrate scope.

Photocatalytic and Chemoselective H/D Exchange at α-Thio C(sp3)-H Bonds

Deuterated compounds used in drug discovery and live-cell imaging have recently gained the attention of various scientific fields. Although hydrogen-deuterium (H/D) exchange reactions are straightforward deuteration methods, achieving perfect chemoselectivity is challenging. We report the highly chemoselective deuteration of α-thio C(sp3)-H bonds using a thioxanthone or anthraquinone organic photocatalyst bearing an aromatic ketone skeleton and D2O as an inexpensive deuterium source under 390 nm irradiation. Notably, incorporation of deuterium at the α-positions of the O/N atoms, benzylic positions, and aromatic rings was not observed. The present chemoselectivity was accomplished via a single electron transfer mechanism between the photocatalyst and S-containing substrates, as proven by laser-induced time-resolved transient absorption spectroscopic measurements. Furthermore, the proposed deuteration method could be applied to various S-containing substrates, including pharmaceuticals and biologically active compounds with high regioselectivities. The available deuterated compounds as novel deuterated alkylation reagents for future drug discovery and materials for Raman imaging were also demonstrated.

Unlocking the potential of hydrogen deuterium exchange via an iterative continuous-flow deuteration process

Labelled compounds bearing hydrogen isotopes are keystones in diverse areas constituting a multi-billion dollar global market including drugs, diagnostics, biology, toxicology and smart materials. While hydrogen deuterium exchange (HDE) methods hold promise as relevant tools for the late-stage and one-step preparation of deuterium-labelled compounds, they often fall short in achieving sufficient isotopic purity combined either with a site-selectivity or with a full deuteration process, highlighting the need for further development and optimisation. This report pinpoints an approach to unlock the potential of HDE using the concept of iterative runs in continuous-flow technology (recirculation process). This closed-loop process grants access now to deuterated compounds with high isotopic purities, labelled at a precise site or perdeuterated on demand, in a fast, productive, and environmentally friendly way.

Deuteration Degree Controllable Synthesis of Aryl Deuteromethyl Ethers Through Dual photoredox and Thiol Catalysis

Herein, we report a facile and efficient deuteration degree controllable method for the preparation of aryl deuteromethyl ethers through dual photoredox and thiol catalysis using phenols as the starting materials and inexpensive D2O and CDCl3 as the deuterium sources. All aryl d1, d2, and d3 deuteromethyl ethers can be precisely prepared with good to excellent yields and deuteration ratios. The reaction operates under mild conditions without the need for high temperatures or high loading of transition metal catalysts, and a wide range of functional groups are well tolerated.

Silver-Catalyzed 1,2-Thiosulfonylation of Alkenes: Development of a Nucleophilic d3-Methylthiolating Reagent

Development of robust d3-methylthiolating reagents represents an attractive synthetic method to access deuterated molecules in the field of drug discovery. Here, we report a straightforward strategy to prepare electrophilic S-methyl-d3 arylsulfonothioates in one-step without column purification. These reagents exhibit good radical reactivity toward silver-catalyzed vicinal thiosulfonylation of alkenes or 1,6-enynes on water. As a result, simultaneous incorporation of both SCD3 and ArSO2 units into unsaturated carbon-carbon bonds with 100% atom economy has been established. Moreover, the ATRA adducts with >99% D incorporation can serve as nucleophilic d3-methylthiolating synthons via retro-Michael addition under mild basic conditions, providing a good alternative in trideuteromethylthiolating alkyl iodides to access corresponding trideuteromethyl sulfides with high efficiency.

Radical Cascade Cyclization of N-(o-Cyanobiaryl)acrylamides with Sulfonium Salts via Synergetic Photoredox and Copper Catalysis

As the magic methyl effect is well acknowledged in pharmaceutical molecules, the development of simple and efficient methods for the installment of methyl groups on complex molecules is highly coveted. Hence, we provide a general strategy for radical cascade cyclization of N-(o-cyanobiaryl)acrylamides by utilizing sulfonium salts as the sources of methyl radical and merging photoredox and copper catalysis. This novel protocol can access a wide variety of methylation or remote thioether-substituted benzo-fused N-heterocycle derivatives, which can be easily transformed into diverse highly valuable sulfone and sulfoximine compounds via late-stage diversification. Moreover, to further demonstrate the synthetic utility of this conversion, the methyl(phenyl)sulfide, which serves as both raw material and byproduct, can be recovered and reused in this transformation. The scale-up experiment for the one-pot two-step process directly offers the target product in good yield under the standard conditions.

Hydrodeuteroalkylation of Unactivated Olefins Using Thianthrenium Salts

Isotopically labeled alkanes play a crucial role in organic and pharmaceutical chemistry. While some deuterated methylating agents are readily available, the limited accessibility of other deuteroalkyl reagents has hindered the synthesis of corresponding products. In this study, we introduce a nickel-catalyzed system that facilitates the synthesis of various deuterium-labeled alkanes through the hydrodeuteroalkylation of d2-labeled alkyl TT salts with unactivated alkenes. Diverging from traditional deuterated alkyl reagents, alkyl thianthrenium (TT) salts can effectively and selectively introduce deuterium at α position of alkyl chains using D2O as the deuterium source via a single-step pH-dependent hydrogen isotope exchange (HIE). Our method allows for high deuterium incorporation, and offers precise control over the site of deuterium insertion within an alkyl chain. This technique proves to be invaluable for the synthesis of various deuterium-labeled compounds, especially those of pharmaceutical relevance.

Deuterated Alkyl Sulfonium Salt Reagents; Importance of H/D Exchange Methods in Drug Discovery

Deuterated drugs (heavy drugs) have recently been spotlighted as a new modality for small-molecule drugs because the pharmacokinetics of pharmaceutical drugs can be enhanced by replacing C-H bonds with more stable C-D bonds at metabolic positions. Therefore, deuteration methods for drug candidates are a hot topic in medicinal chemistry. Among them, the H/D exchange reaction (direct transformation of C-H bonds to C-D bonds) is a useful and straightforward method for creating novel deuterated target molecules, and over 20 reviews on the synthetic methods related to H/D exchange reactions have been published in recent years. Although various deuterated drug candidates undergo clinical trials, approved deuterated drugs possess CD3 groups in the same molecule. However, less diversification, except for the CD3 group, is a problem for future medicinal chemistry. Recently, we developed various deuterated alkyl (dn-alkyl) sulfonium salts based on the H/D exchange reaction of the corresponding hydrogen form using D2O as an inexpensive deuterium source to introduce CD3, CH3CD2, and ArCH2CD2 groups into drug candidates. This concept summarises recent reviews related to H/D exchange reactions and novel reagents that introduce the CD3 group, and our newly developed electrophilic dn-alkyl reagents are discussed.

Trideuteromethylthiolation through Reaction of Arynes, S-Methyl-d3 Sulfonothioate with Sulfonamides or Amides: Access to Trideuteromethylated Sulfilimines

A direct and practical three-component tandem reaction of arynes, S-methyl-d3 sulfonothioate with sulfonamides or amides is developed. The reaction is highly efficient and chemoselective, which allows mild synthesis of trideuteromethylated sulfilimines with broad substrate scope and good functional group compatibility, giving the products in good to excellent yields with 92%-99% deuterium incorporation. Mechanism studies disclosed sulfenamide that generated in situ is the key intermediate for the reaction. This protocol provides potential method for introduction of -SCD3 moiety for deuteration of marked drugs and drug candidates containing sulfilimine skeleton.

Selective Methylation of Nucleosides via an In Situ Generated Methyl Oxonium

A very mild and efficient procedure has been developed for the preparation of N-methylated uridine, pseudouridine, guanosine and inosine derivatives. This process was compatible with free hydroxyls within the ribose and did not require precautions on the protection or deprotection of other functionalities. The key to this extremely mild methylation without protection relied on the in situ generated methyl oxonium from the Wittig reagent and methanol. A putative mechanism for the selective methylation was also proposed.

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.

Sulfonium Salt Reagents for the Introduction of Deuterated Alkyl Groups in Drug Discovery

The pharmacokinetics of pharmaceutical drugs can be improved by replacing C-H bonds with the more stable C-D bonds at the α-position to heteroatoms, which is a typical metabolic site for cytochrome P450 enzymes. However, the application of deuterated synthons is limited. Herein, we established a novel concept for preparing deuterated reagents for the successful synthesis of complex drug skeletons with deuterium atoms at the α-position to heteroatoms. (dn -Alkyl)diphenylsulfonium salts prepared from the corresponding nondeuterated forms using inexpensive and abundant D2 O as the deuterium source with a base, were used as electrophilic alkylating reagents. Additionally, these deuterated sulfonium salts were efficiently transformed into dn -alkyl halides and a dn -alkyl azide as coupling reagents and a dn -alkyl amine as a nucleophile. Furthermore, liver microsomal metabolism studies revealed deuterium kinetic isotope effects (KIE) in 7-(d2 -ethoxy)flavone. The present concept for the synthesis of deuterated reagents and the first demonstration of a KIE in a d2 -ethoxy group will contribute to drug discovery research based on deuterium chemistry.

Sulfonium-based precise alkyl transposition reactions

S-adenosyl-L-methionine (SAM), a sulfonium-based cofactor, plays an important role in numerous biological processes as methyl donor. Inspired by the function of sulfonium motif in this nature's synthetic toolkit, we here present an aryne-activation strategy that the sulfonium intermediates in situ generated from thioethers display unique reactivity toward alkyl group transposition. Experimental and theoretical studies indicate that the reaction occurs in an intermolecular fashion where the TfO--incorporated [K(18-crown-6)] complex acts as a key promoter for this thermodynamically favored process. Next, a series of robust, easy-to-prepare sulfonium salts are designed and developed as electrophilic alkylation reagents accordingly. Both systems feature for broad scope, excellent selectivity, and simple operation. Moreover, we highlight the synthetic value through molecular editing and late-stage modification of complex scaffolds or even active pharmaceutical ingredients.

In situ Generated Iridium Nanoparticles as Hydride Donors in Photoredox-Catalyzed Hydrogen Isotope Exchange Reactions with Deuterium and Tritium Gas

We have studied the photoredox-catalyzed hydrogen isotope exchange (HIE) reaction with deuterium or tritium gas as isotope sources and in situ formed transition metal nanoparticles as hydrogen atom transfer pre-catalysts. By this means we have found synergistic reactivities applying two different HIE mechanisms, namely photoredox-catalyzed and CH-functionalization HIE leading to the synthesis of highly deuterated complex molecules. Finally, we adopted these findings successfully to tritium chemistry.

Direct Trideuteromethylation of Sulfenate Anions Generated In Situ from β-Sulfinyl Esters: An Access to Trideuteromethyl Sulfoxides

Deuterated organic molecules have immense value in the pharmaceutical industry. Here, we present a synthetic strategy for direct trideuteromethylation of sulfenate ions derived in situ from β-sulfinyl esters in the presence of a base utilizing inexpensive and abundant CD₃OTs as the electrophilic trideuteromethylating agent. This protocol provides straightforward access to an array of trideuteromethyl sulfoxides in yields of 75-92% with a high degree of deuteration. The ensuing trideuteromethyl sulfoxide can be readily modified into trideuteromethyl sulfone and sulfoximine.

Cesium Amide-Catalyzed Selective Deuteration of Benzylic C-H Bonds with D2 and Application for Tritiation of Pharmaceuticals

Hydrogen isotope exchange (HIE) represents one of the most attractive labeling methods to synthesize deuterium- and tritium-labeled compounds. Catalytic HIE methods that enable site-selective C-H bond activation and exchange labeling with gaseous isotopes D₂ and T₂ are of vital importance, in particular for high-specific-activity tritiation of pharmaceuticals. As part of our interest in exploring s-block metals for catalytic transformations, we found CsN(SiMe₃ )₂ to be an efficient catalyst for selective HIE of benzylic C-H bonds with D₂ gas. The reaction proceeds through a kinetic deprotonative equilibrium that establishes an exchange pathway between C-H bonds and D₂ gas. By virtue of multiple C-H bonds activation and high activity (isotope enrichment up to 99 %), the simple cesium amide catalyst provided a very powerful and practically convenient labeling protocol for synthesis of highly deuterated compounds and high-specific-activity tritiation of pharmaceuticals.

Facilitating Rh-Catalyzed C-H Alkylation of (Hetero)arenes and 6-Arylpurine Nucleosides (Nucleotides) with Electrochemistry

An electrochemical approach to promote the ortho-C-H alkylation of (hetero)arenes via rhodium catalysis under mild conditions is described. This approach features mild conditions with high levels of regio- and monoselectivity that tolerate a variety of aromatic and heteroaromatic groups and offers a widely applicable method for late-stage diversification of complex molecular architectures including tryptophan, estrone, diazepam, nucleosides, and nucleotides. Alkyl boronic acids and esters and alkyl trifluoroborates are demonstrated as suitable coupling partners. The isolation of key rhodium intermediates and mechanistic studies provided strong support for a rhodium(III/IV or V) regime.

Robust, scalable construction of an electrophilic deuterated methylthiolating reagent: facile access to SCD3-containing scaffolds

We have established a practical and concise method for the straightforward access of a universal deuterated methylthiolating reagent through a one-pot gram-scale operation under mild conditions. This odourless electrophilic SCD₃ reagent was widely applied to react with numerous representative nucleophiles and approached various valuable SCD₃ analogues with excellent levels of deuterium content (>99% D). The divergent further transformations were smoothly carried out to obtain the significant derivatives with different oxidative states in high efficiency.

Recent Developments for the Deuterium and Tritium Labeling of Organic Molecules

Organic compounds labeled with hydrogen isotopes play a crucial role in numerous areas, from materials science to medicinal chemistry. Indeed, while the replacement of hydrogen by deuterium gives rise to improved absorption, distribution, metabolism, and excretion (ADME) properties in drugs and enables the preparation of internal standards for analytical mass spectrometry, the use of tritium-labeled compounds is a key technique all along drug discovery and development in the pharmaceutical industry. For these reasons, the interest in new methodologies for the isotopic enrichment of organic molecules and the extent of their applications are equally rising. In this regard, this Review intends to comprehensively discuss the new developments in this area over the last years (2017-2021). Notably, besides the fundamental hydrogen isotope exchange (HIE) reactions and the use of isotopically labeled analogues of common organic reagents, a plethora of reductive and dehalogenative deuteration techniques and other transformations with isotope incorporation are emerging and are now part of the labeling toolkit.

A desulphurization strategy for Sonogashira couplings by visible light/copper catalysis

We have developed a new copper-based photocatalyst, [(binap)(tpy)Cu]Cl, and applied it in the visible-light promoted Sonogashira coupling reactions.

Alkylsulfonium salts for the photochemical desulphurizative functionalization of heteroarenes

A metal-free organic photoredox-catalyzed alkylation of heteroarenes using alkylsulfonium salts as alkylation reagents has been developed.

Copper-catalysed low-temperature water-gas shift reaction for selective deuteration of aryl halides

The introduction of deuterium atoms into organic compounds is of importance for basic chemistry, material sciences, and the development of drugs in the pharmaceutical industry, specifically for identification and quantification of metabolites. Hence, methodologies for the synthesis of selectively labelled compounds continue to be a major area of interest for many scientists. Herein, we present a practical and stable heterogeneous copper catalyst, which permits for dehalogenative deuteration via water–gas shift reaction at comparably low temperature. This novel approach allows deuteration of diverse (hetero)aryl halides with good functional group tolerance, and no reduction of the aromatic rings or other easily reducible formyl and cyano groups. Multi-gram experiments show the potential of this method in organic synthesis and medicinal chemistry.

A practical and stable heterogeneous copper catalyst has been developed for dehalogenative deuteration via water–gas shift reaction at low temperature, allowing deuteration of diverse (hetero)aryl halides with good functional group tolerance.

Broadening of horizons in the synthesis of CD3-labeled molecules

In the light of the recent potentials of deuterated molecules as pharmaceuticals or even in mechanistic understanding, efficient methods for their synthesis are continually desired. CD₃-containing molecules are prominent amongst these motifs due to the parallel of the "magic methyl effect": introducing a methyl group into pharmaceuticals could positively affect biological activities. The trideuteromethyl group is bound to molecules either by C, N, O, or S atom. For a long time, the preparation methods of such labeled compounds were underestimated and involved multi-step syntheses. More recently, specific approaches dealing with the direct incorporation of the CD₃ group have been developed. This Review gives an overview of the methods for the preparation of CD₃-labeled molecules from conventional functional group interconversion techniques to catalytic approaches and include radical strategy. Detailed reaction mechanisms are also discussed.

The Deuterated "Magic Methyl" Group: A Guide to Site-Selective Trideuteromethyl Incorporation and Labeling by Using CD3 Reagents

In the field of medicinal chemistry, the precise installation of a trideuteromethyl group is gaining ever-increasing attention. Site-selective incorporation of the deuterated "magic methyl" group can provide profound pharmacological benefits and can be considered an important tool for drug optimization and development. This review provides a structured overview, according to trideuteromethylation reagent, of currently established methods for site-selective trideuteromethylation of carbon atoms. In addition to CD3 , the selective introduction of CD2 H and CDH2 groups is also considered. For all methods, the corresponding mechanism and scope are discussed whenever reported. As such, this review can be a starting point for synthetic chemists to further advance trideuteromethylation methodologies. At the same time, this review aims to be a guide for medicinal chemists, offering them the available C-CD3 formation strategies for the preparation of new or modified drugs.

Enabling the Use of Alkyl Thianthrenium Salts in Cross-Coupling Reactions by Copper Catalysis

Alkyl groups are one of the most widely used groups in organic synthesis. Here, a a series of thianthrenium salts have been synthesized that act as reliable alkylation reagents and readily engage in copper-catalyzed Sonogashira reactions to build C(sp³ )-C(sp) bonds under mild photochemical conditions. Diverse alkyl thianthrenium salts, including methyl and disubstituted thianthrenium salts, are employed with great functional breadth, since sensitive Cl, Br, and I atoms, which are poorly tolerated in conventional approaches, are compatible. The generality of the developed alkyl reagents has also been demonstrated in copper-catalyzed Kumada reactions.

Generation of non-stabilized alkyl radicals from thianthrenium salts for C-B and C-C bond formation

Sulfonium salts bearing a positively charged sulfur atom with three organic substituents have intrigued chemists for more than a century for their unusual structures and high chemical reactivity. These compounds are known to undergo facile single-electron reduction to emerge as a valuable and alternative source of aryl radicals for organic synthesis. However, the generation of non-stabilized alkyl radicals from sulfonium salts has been a challenge for several decades. Here we report the treatment of S-(alkyl) thianthrenium salts to generate non-stabilized alkyl radicals as key intermediates granting the controlled and selective outcome of the ensuing reactions under mild photoredox conditions. The value of these reagents has been demonstrated through the efficient construction of alkylboronates and other transformations, including heteroarylation, alkylation, alkenylation, and alkynylation. The developed method is practical, and provides the opportunity to convert C-OH bond to C-B and C-C bonds.

A highly selective decarboxylative deuteration of carboxylic acids

In this paper, we report a mild and practical method for precise deuteration of aliphatic carboxylic acids by synergistic photoredox and HAT catalysis. The reaction delivers excellent D-incorporation (up to 99%) at predicted sites even in substrates bearing reactive C-H bonds or versatile functional groups. The use of a recirculation reactor with a peristaltic pump supports a scalable preparative ability (up to 50 mmol) under very mild reaction conditions. The practical and precise deuteration of readily available complex carboxylic acids makes this protocol promising for the preparation of deuterium-labelled compounds.