Deuterium in drug discovery: progress, opportunities and challenges

Organophotocatalytic Selective Deuteration of Metabolically Labile Heteroatom Adjacent C-H Bonds via H/D Exchange with D2O

We report a general approach for efficient deuteration of the metabolically labile α-C-H bonds of widespread amides and amines. Temporarily masking the secondary amine group as a carbamate allows an unprecedented photoredox hydrogen atom transfer-promoted α-carbamyl radical formation for efficient H/D exchange with D2O. The mild protocol delivers structurally diverse α-deuterated secondary amines including "privileged" piperidine and piperazine structures highly regioselectively with excellent levels of deuterium incorporation (≤100%). Furthermore, we successfully implemented the strategy for α-deuteration of amides, lactams, and ureas with high regioselectivity and high levels of D incorporation. Finally, the observed efficient deuteration of secondary alcohol moieties in late-stage modification of complex amine-containing pharmaceuticals allows for the development of a viable method for efficient α-deuteration of the important functionality.

Diversification of Bipyridines and Azaheterocycles via Nucleophilic Displacement of Trimethylammoniums

Bipyridines and azaarenes are an important class of ligands that impart unique and tunable properties to transition metal complexes and catalysts. While some derivatives are commercially available, noncommercial analogues are often challenging to prepare and purify. Herein, we report a general nucleophilic aromatic substitution reaction that converts cationic trimethylaminated bipyridines into a series of functionalized bipyridines. Our method showcases a series of C-O, C-S, and C-F bond-forming reactions as well as a selective monodemethylation that converts the electron-deficient trimethylammonium to an electron-rich dimethylamine. The approach was further applied to diversification of pharmaceuticals and natural products and was applied to the total synthesis of Graveolinine and the preparation of Graveolinine derivatives.

Deuterated Drugs: Isotope Distribution and Impurity Profiles

A recent review identified the problem of lower isotopologues in deuterated active pharmaceutical ingredients (APIs) as a critical issue in this area of medicinal chemistry. In this Perspective, the relationship between overall enrichment and isotope distribution for deuterated APIs is discussed. Deuterated APIs are divided into single deuterium, methyl-d3, and polydeuterated compounds. For the latter category, distribution calculations demonstrate that the parent deuterated API contains significant quantities of the lower isotopologues. As an alternative to the use of overall enrichment to describe these compounds, it is suggested that describing these compounds with a distribution profile should be preferred, giving an accurate and defensible description of the API. Using this approach, the lower isotopologues become an integral part of the API and not an impurity.

Designing chemical systems for precision deuteration of medicinal building blocks

Methods are lacking that can prepare deuterium-enriched building blocks, in the full range of deuterium substitution patterns at the isotopic purity levels demanded by pharmaceutical use. To that end, this work explores the regio- and stereoselective deuteration of tetrahydropyridine (THP), which is an attractive target for study due to the wide prevalence of piperidines in drugs. A series of d0-d8 tetrahydropyridine isotopomers were synthesized by the stepwise treatment of a tungsten-complexed pyridinium salt with H-/D- and H+/D+. The resulting decomplexed THP isotopomers and isotopologues were analyzed via molecular rotational resonance (MRR) spectroscopy, a highly sensitive technique that distinguishes isotopomers and isotopologues by their unique moments of inertia. In order to demonstrate the medicinal relevance of this approach, eight unique deuterated isotopologues of erythro-methylphenidate were also prepared.

Synthesis and Characterization of DHODH Inhibitors Based on the Vidofludimus Scaffold with Pronounced Anti-SARS-CoV-2 Activity

New strategies for the rapid development of broad-spectrum antiviral therapies are urgently required for emerging and re-emerging viruses like the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Host-directed antivirals that target universal cellular metabolic pathways necessary for viral replication present a promising approach with broad-spectrum activity and low potential for development of viral resistance. Dihydroorotate dehydrogenase (DHODH) was identified as one of those universal host factors essential for the replication of many clinically relevant human pathogenic viruses. DHODH is the rate-limiting enzyme catalyzing the fourth step in the de novo pyrimidine synthesis. Therefore, it is also developed as a therapeutic target for many diseases relying on cellular pyrimidine resources, such as cancer, autoimmune diseases and viral or bacterial infection. Thus, several DHODH inhibitors, including vidofludimus calcium (VidoCa, IMU-838), are currently in development or have been investigated in clinical trials for the treatment of virus infections such as SARS-CoV-2-mediated coronavirus disease 19 (COVID-19). Here, we report the medicinal chemistry optimization of VidoCa that resulted in metabolically more stable derivatives with improved DHODH target inhibition in various mammalian species, which translated into improved efficacy against SARS-CoV-2.

Current emerging therapeutic targets and clinical investigational agents for schizophrenia: Challenges and opportunities

Since the first discovery of antipsychotics in the 1950s, targeting dopaminergic drugs has manifested to well manage the positive symptoms of schizophrenia with limited efficacy for the negative and cognitive symptoms. In past decades, extensive efforts have been undertaken towards the development of innovative agents that can effectively stabilize the dopamine and serotonin systems or target to nondopaminergic pathways, leading to various promising drug candidates entering into clinical trials. Notably, the sigma-2, 5-HT2A, and α1A receptor antagonist roluperidone, as well as a fixed-dose combination of the M1/4 receptor agonist KarXT, have been submitted for NDA applications. The dual agonist ulotaront, which targets TAAR1 and 5-HT1A receptors, and the GlyT1 inhibitor iclepertin have advanced into phase 3 clinical trials. Nevertheless, satisfactory therapeutic strategies for schizophrenia remain elusive. This review highlights current clinical endeavors in developing novel chemical small-molecule entities and fixed-dose combinations for the treatment of schizophrenia since 2017, thus facilitating the efficient development of the next generation of antipsychotics.

Geometric constraints regulated regioselectivity: Pd-catalyzed α-deuteration of pyridines with secondary phosphine oxide

A Pd-catalyzed regioselective H/D exchange at the α-position of pyridines was achieved by employing secondary phosphine oxide as an internal base. The proposed five-membered structure enabled the reaction to overcome its conventional ortho-directing feature, allowing the efficient deuteration of pyridines and quinolines at adjacent sites of N-atoms.

Binary Catalytic Hydrogen/Deuterium Exchange of Free α-Amino Acids and Derivatives

The increasing demand for deuterium-labeled amino acids and derivatives has heightened interest in direct hydrogen/deuterium exchange reactions of free amino acids. Existing methods, including biocatalysis and metal catalysis, typically require expensive deuterium sources or excessive use of deuterium reagents and often struggle with site selectivity. In contrast, this binary catalysis system, employing benzaldehyde and Cs2CO3 in the presence of inexpensive D2O with minimal stoichiometric quantities, facilitates efficient hydrogen/deuterium exchange at the α-position of amino acids without the need for protecting groups in the polar aprotic solvent DMSO. The process is highly compatible with most natural and non-natural α-amino acids and derivatives, even those with potentially reactive functionalities. This advancement not only addresses the cost and efficiency concerns of existing methods but also significantly broadens the applicability and precision of deuterium labeling in biochemical research.

MMFA-DTA: Multimodal Feature Attention Fusion Network for Drug-Target Affinity Prediction for Drug Repurposing Against SARS-CoV-2

The continuous emergence of novel infectious diseases poses a significant threat to global public health security, necessitating the development of small-molecule inhibitors that directly target pathogens. The RNA-dependent RNA polymerase (RdRp) and main protease (Mpro) of SARS-CoV-2 have been validated as potential key antiviral drug targets for the treatment of COVID-19. However, the conventional new drug R&D cycle takes 10-15 years, failing to meet the urgent needs during epidemics. Here, we propose a general multimodal deep learning framework for drug repurposing, MMFA-DTA, to enable rapid virtual screening of known drugs and significantly improve discovery efficiency. By extracting graph topological and sequence features from both small molecules and proteins, we design attention mechanisms to achieve dynamic fusion across modalities. Results demonstrate the superior performance of MMFA-DTA in drug-target affinity prediction over several state-of-the-art baseline methods on Davis and KIBA data sets, validating the benefits of heterogeneous information integration for representation learning and interaction modeling. Further fine-tuning on COVID-19-relevant bioactivity data enhances model predictions for critical SARS-CoV-2 enzymes. Case studies screening the FDA-approved drug library successfully identify etacrynic acid as the potential lead compound against both RdRp and Mpro. Molecular dynamics simulations further confirm the stability and binding affinity of etacrynic acid to these targets. This study proves the great potential and advantages of deep learning and drug repurposing strategies in supporting antiviral drug discovery. The proposed general and rapid response computational framework holds significance for preparedness against future public health events.

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.

Next-generation EGFR tyrosine kinase inhibitors to overcome C797S mutation in non-small cell lung cancer (2019-2024)

Lung cancer is a leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) accounts for the major portion (80-85%) of all lung cancer cases. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are commonly used as the targeted therapy for EGFR-mutated NSCLC. The FDA has approved first-, second- and third-generation EGFR-TKIs as therapeutics options. Osimertinib, the third-generation irreversible EGFR-TKI, has been approved for the treatment of NSCLC patients with the EGFRT790M mutation. However, due to the EGFRC797S mutation in the kinase domain of EGFR, resistance to osimertinib is observed and that limits the long-term effectiveness of the drug. The C797S mutation is one of the major causes of drug resistance against the third-generation EGFR TKIs. The C797S mutations including EGFR double mutations (19Del/C797S or L858R/C797S) and or EGFR triple mutations (19Del/T790M/C797S or L858R/T790M/C797S) cause major resistance to the third-generation EGFR-TKIs. Therefore, the discovery and development of fourth-generation EGFR-TKIs to target triple mutant EGFR with C797S mutation is a challenging topic in medicinal chemistry research. In this review, we discuss the discovery of novel fourth-generation EGFR TKIs, medicinal chemistry approaches and the strategies to overcome the C797S mutations. In vitro activities of EGFR-TKIs (2019-2024) against mutant EGFR TK, anti-proliferative activities, structural modifications, binding modes of the inhibitors and in vivo efficacies in animal models are discussed here.

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.

Pegylated Phosphine Ligands in Iridium(I) Catalyzed Hydrogen Isotope Exchange Reactions in Aqueous Buffers

The synthesis of a water-soluble, phosphine-pegylated iridium(I) catalyst and its application in hydrogen isotope exchange (HIE) reactions in buffer is reported. The longer polyethylene glycol side chains on the phosphine increased the water solubility independently from the pH. HIE reactions of polar substrates in protic solvents were studied. DFT calculations gave further insights into the catalytic processes. The scope and limitation of the pegylated catalyst was studied in HIE reactions of several complex compounds in borax buffer at pH 9 and the best conditions were applied in a tritium experiment with the drug telmisartan.

Ring Rearrangement Reactions of 4-Alkenylisocoumarins and Photophysical Evaluation of Multi-Substituted Anthracene Products

Herein we report that readily available 4-alkenylisocoumarins can be regarded as potent dienolate equivalents. For example, lactol silyl ethers derived from 4-alkenylisocoumarins were selectively converted to the corresponding benzo-homophthalates through a fluoride-induced ring opening step that was followed by a ring closure through a vinylogous intramolecular aldol condensation. Likewise, nucleophilic activation of 4-alkenylisocoumarins directly yields diversely poly-substituted naphthalenes and anthracenes without formation of any regioisomer. Photophysical evaluation of a set of thus obtained 1,3-di- and 1,3,4-trisubstituted anthracenes reveals their distinct intramolecular charge transfer (ICT) character during light absorption in polar solutions and excimer emission from the solid state when a face-to-face π-stacked molecular assembly is present in the crystal packing.

Biological Evaluation of d-[18F]Fluoroalanine and d-[18F]Fluoroalanine-d3 as Positron Emission Tomography Imaging Tracers for Bacterial Infection

d-Amino acids such as d-alanine are substrates for bacterial peptidoglycan biosynthesis and are selectively taken up by bacteria and not mammalian cells. Consequently, d-amino acid metabolism is an attractive target for antibiotic discovery and the development of bacteria-specific imaging agents. d-Fluoroalanine and the deuterium-labeled analogue fludalanine (MK641) were originally explored as antibiotics by Merck but failed in clinical trials due to unaccepted toxicity. Herein, we synthesized a fluorine-18 labeled d-fluoroalanine, d-3-[18F]fluoroalanine (d-[18F]FAla), and its deuterated analogue, d-3-[18F]fluoroalanine-d3 (d-[18F]FAla-d3), and evaluated their capability to image bacterial infection. Both d-[18F]FAla and d-[18F]FAla-d3 can accumulate up to 0.64-0.78% ID/cc in the infectious area at 15 min postinjection. Despite the reduction of in vivo defluorination not being observed for deuterated 18F-labeled d-fluoroalanine, these radiolabeled d-alanine analogues were able to differentiate bacterial infection from sterile inflammation in a soft-tissue model of S. aureus infection.

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.

Separation of isotopologues of amphetamine with various degree of deuteration on achiral and polysaccharide-based chiral columns in high-performance liquid chromatography

Hydrogen/deuterium (H/D) isotope effects are not unusual in chromatography and such phenomena have been observed in both gas- and liquid-phase separations. Despite the numerous reports on this topic, the understanding of mechanisms and the underlying noncovalent interactions at play remains rather challenging. In our recent study, we reported baseline separation of isotopologoues of some amphetamine (AMP) derivatives on achiral and polysaccharide-based chiral columns, as well as some correlations between the degree of separation of enantiomers and isotopologues on (the same) polysaccharide-based chiral column(s). Following our previous findings on isotope effects in high-performance liquid chromatography, we report herein a comparative study on the isotope effects observed with AMP and methamphetamine (MET). The impact of some pivotal factors such as the number of deuterium atoms part of AMP isotopologues, the structure of its isotopomers, the chemical structure of the achiral and chiral stationary phases used in this study, and the use of methanol- vs acetonitrile-containing mobile phases on the isotope effects was examined and discussed. Quantitative correlations between the observed isotope effects and the enantioselectivity of the chiral columns used are also shortly discussed. Furthermore, considering the chromatographic results as benchmark experimental data, we attempted to elucidate the molecular bases of the observed phenomena using quantum mechanics calculations.

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.

Enhanced oxidative stability of deuterated squalene: the impact of labelling extent on chemical resilience

The extent to which deuteration affects the oxidative stability of squalene, a nutrient and a commonly-used ingredient in cosmetics and vaccine adjuvants, has been quantified as a function of the extent of labelling. The formation of comedogenic peroxides was inhibited by levels of overall deuteration as low as 19%.

Divergent and chemoselective deuteration of N-unsubstituted imidazoles enabled by precise acid/base control

Herein, we report acid/base-controlled and divergent deuteration of N-unsubstituted imidazoles in an imidazole-selective manner. This protocol enabled the deuteration of not only the 4-arylimidazoles but also the 2-arylimidazoles without labelling the aromatic rings. We demonstrated the advantages of this protocol by the synthesis of deuterated pharmaceuticals, which is difficult to achieve by means of transition metals.

Photocatalytic deuterocarboxylation of alkynes with oxalate

Herein, a catalytic photoredox-neutral strategy for alkyne deuterocarboxylation with tetrabutylammonium oxalate as the carbonyl source and D2O as the deuteration agent was described. For the first time, the oxalic salt acted as both the reductant and carbonyl source through single electron transfer and subsequential homolysis of the C-C bond. The strongly reductive CO2 radical anion species in situ generated from oxalate played significant roles in realizing the global deuterocarboxylation of terminal and internal alkynes to access various tetra- and tri-deuterated aryl propionic acids with high yields and deuteration ratios.

Synthesis of N-(3-Acyloxyacyl)glycines, Small Molecules with Potential Role in Gut Microbiome-Endocannabinoidome Communication

The synthesis of some N-(3-acyloxyacyl)glycines, an interesting class of bioactive gut microbiota metabolites, is described. This procedure involves seven reaction steps using the commercially available Meldrum's acid to obtain highly pure products, in normal or deuterated form. The key point of the synthetic strategy was the use of commendamide t-butyl ester as a synthetic intermediate, a choice that allowed the removal of the protecting group at the end of the synthetic procedure without degrading of the other ester bond present in the molecule. The developed synthetic sequence is particularly simple, uses readily available reagents and involves a limited number of purifications by chromatographic column, with a reduction in the volume of solvent and energy used.

Digital colloid-enhanced Raman spectroscopy for the pharmacokinetic detection of bioorthogonal drugs

Bioorthogonal drug molecules are currently gaining prominence for their excellent efficacy, safety and metabolic stability. Pharmacokinetic study is critical for understanding their mechanisms and guiding pharmacotherapy, which is primarily performed with liquid chromatography-mass spectrometry as the gold standard. For broader and more efficient applications in clinics and fundamental research, further advancements are especially desired in cheap and portable instrumentation as well as rapid and tractable pretreatment procedures. Surface-enhanced Raman spectroscopy (SERS) is capable of label-free detection of various molecules based on the spectral signatures with high sensitivity even down to a single-molecule level. But limited by irreproducibility at low concentrations and spectral interference in complex biofluids, SERS hasn't been widely applied for pharmacokinetics, especially in live animals. In this work, we propose a new method to quantify bioorthogonal drug molecules with signatures at the spectral silent region (SR) by the digital colloid-enhanced Raman spectroscopy (dCERS) technique. This method was first validated using 4-mercaptobenzonitrile in a mixture of analogous molecules, exhibiting reliable and specific identification capability based on the unique SR signature and Poisson-determined quantification accuracy. We further developed a single-step serum pretreatment method and successfully profiled the pharmacokinetic behavior of an anticancer drug, erlotinib, from animal studies. In a word, this method, superior in sensitivity, controllable accuracy, minimal background interference and facile pretreatment and measurement, promises diverse applications in fundamental studies and clinical tests of bioorthogonal drug molecules.

New and emerging oral therapies for psoriasis

Psoriasis is a chronic inflammatory skin disease affecting 2-3% of the global population. Traditional systemic treatments, such as methotrexate, cyclosporine, acitretin and fumaric acid esters, have limited efficacy and are associated with significant adverse effects, necessitating regular monitoring and posing risks of long-term toxicity. Recent advancements have introduced biologic drugs that offer improved efficacy and safety profiles. However, their high cost and the inconvenience of parenteral administration limit their accessibility. Consequently, there is a growing interest in developing new, targeted oral therapies. Small molecules, such as phosphodiesterase 4 inhibitors (e.g. apremilast) and TYK2 inhibitor (e.g. deucravacitinib), have shown promising results with favourable safety profiles. Additionally, other novel oral agents targeting specific pathways, including IL-17, IL-23, TNF, S1PR1 and A3AR, are under investigation. These treatments aim to combine the efficacy of biologics with the convenience and accessibility of oral administration, addressing the limitations of current therapies. This narrative review synthesizes the emerging oral therapeutic agents for psoriasis, focusing on their mechanisms of action, stages of development and clinical trial results.

Hydrogen Bonding in Amorphous Indomethacin

Amorphous Indomethacin has enhanced bioavailability over its crystalline forms, yet amorphous forms can still possess a wide variety of structures. Here, Empirical Potential Structure Refinement (EPSR) has been used to provide accurate molecular models on the structure of five different amorphous Indomethacin samples, that are consistent with their high-energy X-ray diffraction patterns. It is found that the majority of molecules in amorphous Indomethacin are non-bonded or bonded to one neighboring molecule via a single hydrogen bond, in contrast to the doubly bonded dimers found in the crystalline state. The EPSR models further indicate a substantial variation in hydrogen bonding between different amorphous forms, leading to a diversity of chain structures not found in any known crystal structures. The majority of hydrogen bonds are associated with the carboxylic acid group, although a significant number of amide hydrogen bonding interactions are also found in the models. Evidence of some dipole-dipole interactions are also observed in the more structurally ordered models. The results are consistent with a distribution of Z-isomer intramolecular type conformations in the more disordered structures, that distort when stronger intermolecular hydrogen bonding occurs. The findings are supported by 1H and 2H NMR studies of the hydrogen bond dynamics in amorphous Indomethacin.

An Update on the Nitrogen Heterocycle Compositions and Properties of U.S. FDA-Approved Pharmaceuticals (2013-2023)

This Perspective is a continuation of our analysis of U.S. FDA-approved small-molecule drugs (1938-2012) containing nitrogen heterocycles. In this study we report drug structure and property analyses of 321 unique new small-molecule drugs approved from January 2013 to December 2023 as well as information about frequency of important heteroatoms such as sulfur and fluorine and key small nitrogen substituents (CN and NO2). The most notable change is an incredible increase in drugs containing at least one nitrogen heterocycle─82%, compared to 59% from preceding decades─as well as a significant increase in the number of nitrogen heterocycles per drug. Pyridine has claimed the #1 high-frequency nitrogen heterocycle occurrence spot from piperidine (#2), with pyrimidine (#5), pyrazole (#6), and morpholine (#9) being the big top 10 climbers. Also notable is high number of fused nitrogen heterocycles, apparently driven largely by newly approved cancer drugs.

Ni/Photoredox-Catalyzed Enantioselective Acylation of α-Bromobenzoates with Aldehydes: A Formal Approach to Aldehyde-Aldehyde Cross-Coupling

The catalytic cross-coupling of identical or similar functional groups is a cornerstone strategy for carbon-carbon bond formation, as exemplified by renowned methods, such as olefin cross-metathesis, Kolbe electrolysis, and various cross-electrophile couplings. However, similar methodologies for coupling aldehydes─fundamental building blocks in organic synthesis─remain underdeveloped. While the benzoin-type condensation, first reported in 1832, offers a reliable route for aldehyde dimerization, the chemo- and enantioselective cross-coupling of nonidentical yet similar aldehydes remains an unsolved challenge. Herein, we report a unified platform enabling highly chemo- and enantioselective cross-coupling of aldehydes. By leveraging nickel photoredox catalysis in tandem with discrete activation strategies for each aldehyde, this mechanistically distinct approach facilitates the enantioselective union of an aldehyde-derived α-oxy radical with an acyl radical, photocatalytically generated from a distinct aldehyde. This novel strategy enables modular access to enantioenriched α-oxygenated ketones with two minimally differentiated aliphatic substituents, a feat not achievable with existing chemocatalytic or biocatalytic techniques. The synthetic utility of this method is demonstrated by its application in the streamlined asymmetric synthesis of various medicinally relevant molecules. Additionally, mechanistic investigations rationalize the versatility of nickel photoredox catalysis to exploit new pathways for addressing long-standing synthetic challenges.

Chemoenzymatic Synthesis of Fluorinated Mycocyclosin Enabled by the Engineered Cytochrome P450-Catalyzed Biaryl Coupling Reaction

Installing fluorine atoms onto natural products holds great promise for the generation of fluorinated molecules with improved or novel pharmacological properties. The enzymatic oxidative carbon-carbon coupling reaction represents a straightforward strategy for synthesizing biaryl architectures, but the exploration of this method for producing fluorine-substituted derivatives of natural products remains elusive. Here, in this study, we report the protein engineering of cytochrome P450 from Mycobacterium tuberculosis (MtCYP121) for the construction of a series of new-to-nature fluorine-substituted Mycocyclosin derivatives. This protocol takes advantage of a "hybrid" chemoenzymatic procedure consisting of tyrosine phenol lyase-catalyzed fluorotyrosine preparation from commercially available fluorophenols, intermolecular chemical condensation to give cyclodityrosines, and an engineered MtCYP121-catalyzed intramolecular biphenol coupling reaction to complete the strained macrocyclic structure. Computational mechanistic studies reveal that MtCYP121 employs Cpd I to abstract a hydrogen atom from the proximal phenolic hydroxyl group of the substrate to trigger the reaction. Then, conformational change makes the two phenolic hydroxyl groups close enough to undergo intramolecular hydrogen atom transfer with the assistance of a pocket water molecule. The final diradical coupling process completes the intramolecular C-C bond formation. The efficiency of the biaryl coupling reaction was found to be influenced by various fluorine substitutions, primarily due to the presence of distinct binding conformations.

Electroreductive deuteroarylation of alkenes enabled by an organo-mediator

Electroreduction mediated by organo-mediators has emerged as a concise and effective strategy, holding significant potential in the site-specific introduction of deuterium. In this study, we present an environmentally friendly electroreduction approach for anti-Markovnikov selective deuteroarylation of alkenes and aryl iodides with D2O as the deuterium source. The key to the protocol lies in the employment of a catalytic amount of 2,2'-bipyiridine as an efficient organo-mediator, which facilitates the generation of aryl radicals by assisting in the cleavage of the C-X (X = I or Br) bonds in aryl halides. Because its reduction potential matches that of aryl iodides, the organo-mediator can control the chemoselectivity of the reaction and avoid the side reactions of competitive substrate deuteration. These phenomena are theoretically supported by CV experiments and DFT calculations. Our protocol provides a series of mono-deuterated alkylarenes with excellent deuterium incorporation through two single-electron reductions (SER), without requiring metal catalysts, external reductants, and sacrificial anodes.

The biological impact of deuterium and therapeutic potential of deuterium-depleted water

Since its discovery by Harold Urey in 1932, deuterium has attracted increased amounts of attention from the scientific community, with many previous works aimed to uncover its biological effects on living organisms. Existing studies indicate that deuterium, as a relatively rare isotope, is indispensable for maintaining normal cellular function, while its enrichment and depletion can affect living systems at multiple levels, including but not limited to molecules, organelles, cells, organs, and organisms. As an important compound of deuterium, deuterium-depleted water (DDW) possess various special effects, including but not limited to altering cellular metabolism and potentially inhibiting the growth of cancer cells, demonstrating anxiolytic-like behavior, enhancing long-term memory in rats, reducing free radical oxidation, regulating lipid metabolism, harmonizing indices related to diabetes and metabolic syndrome, and alleviating toxic effects caused by cadmium, manganese, and other harmful substances, implying its tremendous potential in anticancer, neuroprotective, antiaging, antioxidant, obesity alleviation, diabetes and metabolic syndrome treatment, anti-inflammatory, and detoxification, thereby drawing extensive attention from researchers. This review comprehensively summarizes the latest progress in deuterium acting on living organisms. We start by providing a snapshot of the distribution of deuterium in nature and the tolerance of various organisms to it. Then, we discussed the impact of deuterium excess and deprivation, in the form of deuterium-enriched water (DEW) and deuterium-depleted water (DDW), on living organisms at different levels. Finally, we focused on the potential of DDW as an adjuvant therapeutic agent for various diseases and disorders.

Deuterium Editing of Small Molecules: A Case Study on Antitumor Activity of 1,4-Benzodiazepine-2,5-dione Derivatives

Substituting hydrogen with deuterium in drug molecules is an appealing bioisosteric strategy for the generation of novel chemical entities in drug development. Optimizing lead compounds through deuteration has proven to be challenging and unpredictable, particularly for compounds with multiple metabolic sites. This study presents the pioneering achievement of substituting up to 19 hydrogen atoms with deuterium on 1,4-benzodiazepine-2,5-dione derivatives, shedding light on the structure-metabolism relationship and the impact of multiple deuterations on drug-like properties. Notably, the deuterated compound 3f exhibited remarkable antitumor activity in vivo and demonstrated favorable drug-like properties as a drug candidate.

Isotopologues of potassium 2,2,2-trifluoroethoxide for applications in positron emission tomography and beyond

The 2,2,2-trifluoroethoxy group increasingly features in drugs and potential tracers for biomedical imaging with positron emission tomography (PET). Herein, we describe a rapid and transition metal-free conversion of fluoroform with paraformaldehyde into highly reactive potassium 2,2,2-trifluoroethoxide (CF3CH2OK) and demonstrate robust applications of this synthon in one-pot, two-stage 2,2,2-trifluoroethoxylations of both aromatic and aliphatic precursors. Moreover, we show that these transformations translate easily to fluoroform that has been labeled with either carbon-11 (t1/2 = 20.4 min) or fluorine-18 (t1/2 = 109.8 min), so allowing the appendage of complex molecules with a no-carrier-added 11C- or 18F- 2,2,2-trifluoroethoxy group. This provides scope to create candidate PET tracers with radioactive and metabolically stable 2,2,2-trifluoroethoxy moieties. We also exemplify syntheses of isotopologues of potassium 2,2,2-trifluoroethoxide and show their utility for stable isotopic labeling which can be of further benefit for drug discovery and development.

The role of the methoxy group in approved drugs

The methoxy substituent is prevalent in natural products and, consequently, is present in many natural product-derived drugs. It has also been installed in modern drug molecules with no remnant of natural product features because medicinal chemists have been taking advantage of the benefits that this small functional group can bestow on ligand-target binding, physicochemical properties, and ADME parameters. Herein, over 230 methoxy-containing small-molecule drugs, as well as several fluoromethoxy-containing drugs, are presented from the vantage point of the methoxy group. Biochemical mechanisms of action, medicinal chemistry SAR studies, and numerous X-ray cocrystal structures are analyzed to identify the precise role of the methoxy group for many of the drugs and drug classes. Although the methoxy substituent can be considered as the hybridization of a hydroxy and a methyl group, the combination of these functionalities often results in unique effects that can amount to more than the sum of the individual parts.

A Spontaneous Heavy Hydrogen Generator via a Protium Redox

The extreme significance of heavy hydrogen (D2) in medicinal, nuclear, and chemical sectors, despite its scarce natural abundance, underscores the vital imperative for inventing novel chemistries for its production. We showcase a spontaneous heavy hydrogen generator during commensurate electrical energy production by decoupling the direct chemistry of OD-/D+ dual ions via a protium redox. This exergonic electrochemistry yields ∼357 mL of D2 in nearly 85 h of continuous operation, with a commensurate electrical energy output of 122 kJ/per mole of D2. This laboratory-level demonstration of spontaneous heavy hydrogen production presents a novel chemistry for the scalable manufacture of nonprimordial D2.

Palladium(II)-Catalyzed Nondirected Late-Stage C(sp2)-H Deuteration of Heteroarenes Enabled Through a Multi-Substrate Screening Approach

The importance of deuterium labelling in a variety of applications, ranging from mechanistic studies to drug-discovery, has spurred immense interest in the development of new methods for its efficient incorporation in organic, and especially in bioactive molecules. The five-membered heteroarenes at the center of this work are ubiquitous motifs in bioactive molecules and efficient methods for the deuterium labelling of these compounds are therefore highly desirable. However, the profound differences in chemical properties encountered between different heteroarenes hamper the development of a single set of broadly applicable reaction conditions, often necessitating a separate optimization campaign for a given type of heteroarene. In this study we describe the use of a multi-substrate screening approach to identify optimal reaction conditions for different classes of heteroarenes from a minimal number of screening reactions. Using this approach, four sets of complementary reaction conditions derived from our dual ligand-based palladium catalysts for nondirected C(sp2)-H activation were identified, that together enable the deuteration of structurally diverse heteroarenes, including bioactive molecules.

Synthesis and Biological Evaluation of Fluorine-18 and Deuterium Labeled l-Fluoroalanines as Positron Emission Tomography Imaging Agents for Cancer Detection

To fully explore the potential of 18F-labeled l-fluoroalanine for imaging cancer and other chronic diseases, a simple and mild radiosynthesis method has been established to produce optically pure l-3-[18F]fluoroalanine (l-[18F]FAla), using a serine-derivatized, five-membered-ring sulfamidate as the radiofluorination precursor. A deuterated analogue, l-3-[18F]fluoroalanine-d3 (l-[18F]FAla-d3), was also prepared to improve metabolic stability. Both l-[18F]FAla and l-[18F]FAla-d3 were rapidly taken up by 9L/lacZ, MIA PaCa-2, and U87MG cells and were shown to be substrates for the alanine-serine-cysteine (ASC) amino acid transporter. The ability of l-[18F]FAla, l-[18F]FAla-d3, and the d-enantiomer, d-[18F]FAla-d3, to image tumors was evaluated in U87MG tumor-bearing mice. Despite the significant bone uptake was observed for both l-[18F]FAla and l-[18F]FAla-d3, the latter had enhanced tumor uptake compared to l-[18F]FAla, and d-[18F]FAla-d3 was not specifically taken up by the tumors. The enhanced tumor uptake of l-[18F]FAla-d3 compared with its nondeuterated counterpart, l-[18F]FAla, warranted the further biological investigation of this radiotracer as a potential cancer imaging agent.

The Versatile and Strategic O-Carbamate Directed Metalation Group in the Synthesis of Aromatic Molecules: An Update

The aryl O-carbamate (ArOAm) group is among the strongest of the directed metalation groups (DMGs) in directed ortho metalation (DoM) chemistry, especially in the form Ar-OCONEt2. Since the last comprehensive review of metalation chemistry involving ArOAms (published more than 30 years ago), the field has expanded significantly. For example, it now encompasses new substrates, solvent systems, and metalating agents, while conditions have been developed enabling metalation of ArOAm to be conducted in a green and sustainable manner. The ArOAm group has also proven to be effective in the anionic ortho-Fries (AoF) rearrangement, Directed remote metalation (DreM), iterative DoM sequences, and DoM-halogen dance (HalD) synthetic strategies and has been transformed into a diverse range of functionalities and coupled with various groups through a range of cross-coupling (CC) strategies. Of ultimate value, the ArOAm group has demonstrated utility in the synthesis of a diverse range of bioactive and polycyclic aromatic compounds for various applications.

Ruthenium Complexes with NNN-Pincer Ligands for N-Methylation of Amines Using Methanol

A series of ruthenium complexes (Ru1-Ru4) bearing new NNN-pincer ligands were synthesized in 58-78% yields. All of the complexes are air and moisture stable and were characterized by IR, NMR, and high-resolution mass spectra (HRMS). In addition, the structures of Ru1-Ru3 were confirmed by X-ray crystallographic analysis. These Ru(II) complexes exhibited high catalytic efficiency and broad functional group tolerance in the N-methylation reaction of amines using CH3OH as both the C1 source and solvent. Experimental results indicated that the electronic effect of the substituents on the ligands considerably affects the catalytic reactivity of the complexes in which Ru3 bearing an electron-donating OMe group showed the highest activity. Deuterium labeling and control experiments suggested that the dehydrogenation of methanol to generate ruthenium hydride species was the rate-determining step in the reaction. Furthermore, this protocol also provided a ready approach to versatile trideuterated N-methylamines under mild conditions using CD3OD as a deuterated methylating agent.

H/D Exchange of Aromatic Sulfones via Base Promotion and Silver Catalysis

Aromatic sulfones are the prevailing scaffolds in pharmaceutical and material sciences. However, compared to their widespread application, the selective deuterium labeling of these structures is restricted due to their electron-deficient properties. This study presents two comprehensive strategies for the deuteration of aromatic sulfones. The base-promoted deuteration uses DMSO-d6 as the deuterium source, resulting in a rapid H/D exchange within 2 h. Meanwhile, a silver-catalyzed protocol offers a much milder option by using economical D2O to furnish the labeled sulfones.

Microenvironment regulation breaks the Faradaic efficiency-current density trade-off for electrocatalytic deuteration using D2O

The high Faradaic efficiency (FE) of the electrocatalytic deuteration of organics with D2O at a large current density is significant for deuterated electrosynthesis. However, the FE and current density are the two ends of a seesaw because of the severe D2 evolution side reaction at nearly industrial current densities. Herein, we report a combined scenario of a nanotip-enhanced electric field and surfactant-modified interface microenvironment to enable the electrocatalytic deuteration of arylacetonitrile in D2O with an 80% FE at -100 mA cm-2. The increased concentration with low activation energy of arylacetonitrile due to the large electric field along the tips and the accelerated arylacetonitrile transfer and suppressed D2 evolution by the surfactant-created deuterophobic microenvironment contribute to breaking the trade-off between a high FE and large current density. Furthermore, the application of our strategy in other deuteration reactions with improved Faradaic efficiencies at -100 mA cm-2 rationalizes the design concept.

Deuteration-Driven Photopharmacology: Deuterium-Labeled for Controlling Alpha 7 Nicotinic Acetylcholine Receptors

Photopharmacology is a powerful approach to investigate biological processes and overcomes the common therapeutic challenges in drug development. Enhancing the photopharmacology properties of photoswitches contributes to extend their applications. Deuteration, a tiny structural modification, makes it possible to improve the photopharmacology and photophysical properties of prototype compounds, avoiding extra complex chemical changes or constructing multicomponent systems. In this work, we developed a series of D-labeled azobenzenes to expand the azobenzene photoswitchable library and introduced the D-labeled azobenzene unit into the photoagonist of α7 nicotinic acetylcholine receptors (α7 nAChRs) to investigate the effects of deuteration in photopharmacology. Spectral data indicated that deuteration maintained most of the photophysical properties of azobenzenes. The D-labeled photoagonist exhibited good control of the activity of α7 nAChRs than the prototype photoagonist. These results confirmed that deuteration is a promising strategy to improve the photopharmacological properties.

Electroreductive alkylations of (hetero)arenes with carboxylic acids

Carboxylic acids are widely available and generally inexpensive from abundant biomass feedstocks, and they are suitable and generic coupling partners in synthetic chemistry. Reported herein is an electroreductive coupling of stable and versatile carboxylic acids with (hetero)arenes using protons as the hydrogen source. The application of an earth-abundant titanium catalyst has significantly improved the deoxygenative reduction process. Preliminary mechanistic studies provide insights into the deoxygenative reduction of in-situ generated ketone pathway, and the intermediacy generation of ketyl radical and alkylidene titanocene. Without the necessity of pressurized hydrogen or stoichiometric hydride as reductants, this protocol enables highly selective and straightforward synthesis of various functionalized and structurally diverse alkylbenzenes under mild conditions. The utility of this reaction is further demonstrated through practical and valuable isotope incorporation from readily available deuterium source.

Cross-selective Deoxygenative Coupling of Aliphatic Alcohols: Installation of Methyl Groups including Isotopic Labels by Nickel Catalysis

Nickel-catalyzed cross-electrophile coupling reactions of two aliphatic alcohol derivatives remain a challenge. Herein, we report a nickel-catalyzed reductive methylation reaction of aliphatic mesylates with methyl tosylate. This reaction provides straightforward access to compounds bearing aliphatic methyl groups from alkyl alcohol derivatives. Isotopically labelled substrates and reagents can be employed in the reaction to provide perdeuterated and 13C-labelled products. This transformation can be achieved by employing stoichiometric Mn reductant or electrochemically. Additionally, mechanistic experiments show that alkyl iodides are key intermediates in the transformation which undergo a stereoablative reaction via radical intermediates.

Trends in amorphous solid dispersion drug products approved by the U.S. Food and Drug Administration between 2012 and 2023

Forty-eight (48) drug products (DPs) containing amorphous solid dispersions (ASDs) have been approved by the U.S. Food and Drug Administration in the 12-year period between 2012 and 2023. These DPs comprise 36 unique amorphous drugs. Ten (10) therapeutic categories are represented, with most DPs containing antiviral and antineoplastic agents. The most common ASD polymers are copovidone (49%) and hypromellose acetate succinate (30%), while spray drying (54%) and hot melt extrusion (35%) are the most utilized manufacturing processes to prepare the ASD drug product intermediate (DPI). Tablet dosage forms are the most common, with several capsule products available. Line extensions of several DPs based on flexible oral solids and powders for oral suspension have been approved which provide patient-centric dosing to pediatric and other patient populations. The trends in the use of common excipients and film coating types are discussed. Eighteen (18) DPs are fixed-dose combinations, and some contain a mixture of amorphous and crystalline drugs. The DPs have dose/unit of amorphous drug ranging from <5 mg up to 300 mg, with the majority being ≤100 mg/unit. This review details several aspects of DPI and DP formulation and manufacturing of ASDs, as well as trends related to therapeutic category, dose, and patient-centricity.

Investigation of the structure of protein-polymer conjugates in solution reveals the impact of protein deuteration and the size of the polymer on its thermal stability

The conjugation of proteins with polymers offers immense biotechnological potential by creating novel macromolecules. This article presents experimental findings on the structural properties of maltose-binding protein (MBP) conjugated with linear biodegradable polyphosphoester polymers with different molecular weights. We studied isotopic effects on both proteins and polymers. Circular dichroism and fluorescence spectroscopy and small-angle neutron scattering reveal that the conjugation process destabilizes the protein, affecting the secondary more than the tertiary structure, even at room temperature, and that the presence of two domains in the MBP may contribute to its observed instability. Notably, unfolding temperatures differ between native MBP and the conjugates. In particular, this study sheds light on the complex interplay of factors such as the deuteration influencing protein stability and conformational changes in the conjugation processes. The perdeuteration influences the hydrogen bond network and hydrophobic interactions in the case of the MBP protein. The perdeuteration of the protein influences the hydrogen bond network and hydrophobic interactions. This is evident in the decreased thermal stability of deuterated MBP protein, in the conjugate, especially with high-molecular-mass polymers.

Labeling of methyl groups: a streamlined protocol and guidance for the selection of 2H precursors based on molecular weight

A streamlined one-day protocol is described to produce isotopically methyl-labeled protein with high levels of deuterium for NMR studies. Using this protocol, the D2O and 2H-glucose content of the media and protonation level of ILV labeling precursors (ketobutyrate and ketovalerate) were varied. The relaxation rate of the multiple-quantum (MQ) state that is present during the HMQC-TROSY pulse sequence was measured for different labeling schemes and this rate was used to predict upper limits of molecular weights for various labeling schemes. The use of deuterated solvents (D2O) or deuterated glucose is not required to obtain 1H-13C correlated NMR spectra of a 50 kDa homodimeric protein that are suitable for assignment by mutagenesis. High quality spectra of 100-150 kDa proteins, suitable for most applications, can be obtained without the use of deuterated glucose. The proton on the β-position of ketovalerate appears to undergo partial exchange with deuterium under the growth conditions used in this study.

Electrochemical γ-Selective Deuteration of Pyridines

Herein, we first report a γ-selective deuteration reaction of pyridines via H/D exchange without the need for preinstalled directing groups and transformable functional groups. The electrochemical process offers an attractive approach to producing γ-deuterated pyridines under gentle conditions. The broad substrate scope, excellent deuterium incorporation, and remarkable selectivity of the electrochemical method make it applicable for the late-stage modification of pharmaceutical molecules.

Electrochemical benzylic deuteration of p-QMs enabling the synthesis of benzylic deuterated diarylmethanes

Herein, electroreductive umpolung benzylic deuteration of p-QMs using cheap and easily accessible D2O as a deuterium source is reported. Various value-added benzylic deuterated diarylmethanes can be synthesized without the requirement of noble metal catalysts, redox reagents, and strong bases. The establishment of this protocol will provide an alternative strategy for acquiring benzylic deuterated diarylmethanes.

Photosynthesis of C-1-Deuterated Aldehydes via Chlorine Radical-Mediated Selective Deuteration of the Formyl C-H Bond

C-1-deuterated aldehydes are essential building blocks in the synthesis of deuterated chemicals and pharmaceuticals. This has led chemists to devise mild methodologies for their efficient production. Ideally, hydrogen-deuterium exchange (HDE) is the most effective approach. However, the traditional HDE for creating C-1-deuterated aldehydes often requires a complex system involving multiple catalysts and/or ligands. In this study, we present a mild photocatalytic HDE of the formyl C-H bond with D2O. This process is facilitated by chlorine radicals that are generated in situ from low-cost FeCl3. This strategy demonstrated a broad reaction scope and high functional group tolerance, affording good yields and ≤99% D incorporation. To bridge the gap between research and industrial applications, we designed a new flow photoreactor equipped with a high-intensity light-emitting diode bucket, enabling the synthesis of C-1-deuterated aldehydes on a scale of 85 g. Finally, we successfully produced several important deuterated aldehydes that are integral to the synthesis of deuterated pharmaceuticals.

Palladium-Catalyzed Divergent Enantioselective Functionalization of Cyclobutenes

Aliphatic strained rings have been increasingly applied in medicinal chemistry due to their beneficial physicochemical and pharmacokinetic properties. However, the divergent synthesis of enantioenriched cyclobutane derivatives with various structural patterns continues to be a significant challenge. Here, we disclose a palladium-catalyzed enantioselective desymmetrization of cyclobutenes, resulting in a series of hydroarylation and 1,2- and 1,3-diarylation products via the interceptions of a common Heck intermediate. Mechanistic investigations provide valuable insights into understanding the catalytic mode of the palladium catalysts and the observed variations in the deuterium-responsive behavior during reactions. Furthermore, the synthetic utility is demonstrated in the syntheses of deuterated drug candidate belaperidone skeletons and pseudosymmetrical truxinic acid-type derivatives.