A low-viscous and flowable zwitterionic liquid

Zwitterionic liquids have attracted significant attention in various fields due to their low-toxicity and the ability to tune their functional properties. However, despite being liquid in thermo-dynamic definition, zwitterionic liquids are not commonly recognized as "liquids" by the general public because of their extremely high viscosity, comparable to that of peanut butter, which prevents stirring even with a strong magnetic stirrer. In this study, we developed a flowable and stirrable zwitterionic liquid, OE2imOE3C. Its viscosity was one-seventeenth that of traditional zwitterionic liquids. OE2imOE3C was able to stir and dissolve 11 wt% cellulose at 100 °C, which is a task unachievable by a typical zwitterionic liquid due to their high viscosity. Furthermore, OE2imOE3C exhibited low toxicity to yeast, consistent with other standard zwitterionic liquids. This study successfully achieved a significant reduction in viscosity without compromising other properties.

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.

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.

Hydrogenative alkene perdeuteration aided by a transient cooperative ligand

Deuterogenation of unsaturated organic compounds is an attractive route for installing C(sp3)-D bonds, but the existing methods typically use expensive D2 and introduce only two deuterium atoms per unsaturation. Herein we report the hydrogenative perdeuteration of alkenes using readily available H2 and D2O instead of D2, catalysed by an acridanide-based ruthenium pincer complex and resulting in the incorporation of up to 4.9 D atoms per C=C double bond in a single synthetic step. Importantly, adding a catalytic amount of thiol, which serves as a transient cooperative ligand, ensures the incorporation of deuterium rather than protium by balancing the rates of two sequential deuteration processes. The current method opens an avenue for installing perdeuteroalkyl groups at specific sites from widely available alkenes under mild conditions.

Ru Supported on p-phthalic acid-Mn Derived from a Mn Metal-Organic Framework for Thermo- and Electrocatalytic Synthesis of Ethylene-D4 Glycol

Deuterium-labeled polyols are one of the most extensive applied chemicals in biochemistry and biophysics. However, the deuteriation still is insufficient, exhibiting a low deuterated ratio and indistinct reaction mechanism. Herein, Ru supported on MnBCD (MnBDC, derived from Mn p-phthalic acid metal-organic framework) as nanocatalyst with an agglomerated sheet-type structure; this allows the possibility of achieving both thermo- and electrocatalytic hydrogen isotope exchange (HIE) reaction. Furthermore, XPS characterization confirmed that the specific structural changes in the electron density of Ru outer layers were modulated through the impregnation and reduction processes. According to the change of outer electronic structure, hydrogen spillover and electron-rich flow promote the reaction of the catalyst in thermo- and electrocatalytic systems, respectively. In addition, the results indicate that a high deuterated ratio of 97 % can be obtained, hence the catalytic technology has enormous potential for the synthesis of a broad variety of deuterium-labeled compounds.

Heavy water recycling for producing deuterium compounds

Deuterium oxide (D2O) is a special variety of water that serves as a crucial resource in a range of applications, but it is a costly and unusual resource. We therefore developed a new D2O concentration system that combines a polymer electrolyte water electrolyzer and a catalytic combustor for recycling used D2O. In this study, 1.6 L of used D2O, with a concentration of 93.1%, was electrolyzed for 13.6 h to obtain 0.62 L of D2O, with a concentration of 99.3%. In addition, the recombined water obtained by burning electrolytic gas using the catalytic combustor was also electrolyzed for 8.8 h to obtain 0.22 L of D2O, with a concentration of 99.0%. The estimated separation factor of this electrolyzer at 25 °C was 3.6, which is very close to the equilibrium constant of the water/hydrogen isotope exchange reaction. Recycled D2O was used as a deuterium source for the deuteration reaction of sodium octanoate, and 93.6% deuterated sodium octanoate was obtained. It is concluded that there were no impurities in the recycled D2O that interfered with the deuteration reaction. These results can lead to the development of a cost-effective deuteration method for these materials.

Investigation of Parameter Control for Electrocatalytic Semihydrogenation in a Proton-Exchange Membrane Reactor Utilizing Bayesian Optimization

Owing to its applicability in sustainable engineering, flow electrochemical synthesis in a proton-exchange membrane (PEM) reactor has attracted considerable attention. Because the reactions in PEM reactors are performed under electro-organic and flow-synthetic conditions, a higher number of reaction parameters exist compared to ordinary reactions. Thus, the optimization of such reactions requires significant amounts of energy, time, chemical and human resources. Herein, we show that the optimization of alkyne semihydrogenation in PEM reactors can be facilitated by means of Bayesian optimization, an applied mathematics strategy. Applying the optimized conditions, we also demonstrate the generation of a deuterated Z-alkene.

Hydrogen/Deuterium Transfer from Anisole to Methoxy Radicals: A Theoretical Study of a Deuterium-Labeled Drug Model

Recently, deuterium-labeled drugs, such as deutetrabenazine, have attracted considerable attention. Consequently, understanding the reaction mechanisms of deuterium-labeled drugs is crucial, both fundamentally and for real applications. To understand the mechanisms of H- and D-transfer reactions, in this study, we used deuterated anisole as a deutetrabenazine model and computationally considered the nuclear quantum effects of protons, deuterons, and electrons. We demonstrated that geometrical differences exist in the partially and fully deuterated methoxy groups and hydrogen-bonded structures of intermediates and transition states due to the H/D isotope effect. The observed geometrical features and electronic structures are ascribable to the different nuclear quantum effects of protons and deuterons. Primary and secondary kinetic isotope effects (KIEs) were calculated for H- and D-transfer reactions from deuterated and undeuterated anisole, with the calculated primary KIEs in good agreement with the corresponding experimental data. These results reveal that the nuclear quantum effects of protons and deuterons need to be considered when analyzing the reaction mechanisms of H- and D-transfer reactions and that a theoretical approach that directly includes nuclear quantum effects is a powerful tool for the analysis of H/D isotope effects in H- and D-transfer reactions.

Platinum on Carbon-Catalysed Site-Selective H-D Exchange Reaction of Allylic Alcohols Using Alkyl Amines as a Hydrogen Source

We developed platinum on carbon-catalysed deuteration reaction of tert-allylic alcohols using deuterium oxide as a deuterium source. Amylamine was dehydrogenated by platinum on carbon to generate an appropriate amount of...

Synthesis of deuterium-labeled cinnamic acids: Understanding the volatile benzenoid pathway in the flowers of the Japanese loquat Eriobotrya japonica

Cinnamic acids are widely distributed in plants, including crops for human use, and exhibit a variety of activities that are beneficial to human health. They also occupy a pivotal position in the biosynthesis of phenylpropanoids such as lignins, anthocyanins, flavonoids, and coumarins. In this context, deuterium-labeled cinnamic acids have been used as tracers and internal standards in food and medicinal chemistry as well as plant biochemistry. Therefore, a concise synthesis of deuterium-labeled cinnamic acids would be highly desirable. In this study, we synthesized deuterium-labeled cinnamic acids using readily available deuterium sources. We also investigated a hydrogen-deuterium exchange reaction in an ethanol-d₁ /Et₃ N system. This method can introduce deuterium atoms at the ortho and para positions of the phenolic hydroxy groups as well as at the C-2 position of alkyl cinnamates and is applicable to various phenolic compounds. Using the synthesized labeled compounds, we demonstrated that the benzenoid volatiles, such as 4-methoxybenzaldehyde, in the scent of the flowers of the Japanese loquat Eriobotrya japonica are biosynthesized from phenylalanine via cinnamic and 4-coumaric acids. This study provides easy access to a variety of deuterium-labeled (poly)phenols, as well as to useful tools for studies of the metabolism of cinnamic acids in living systems.

Direct deuteration of hinokitiol and its mechanistic study

Hinokitiol has a broad antibacterial activity against bacteria and fungi. While its biosynthetic pathway has been intensively studied, its dynamics in natural environments, such as biodegradation pathway, remain unclear. In this study, the authors report a direct deuterium labeling of hinokitiol as a traceable molecular probe to serve those studies. Hinokitiol was subjected to the H2-Pd/C-D2O conditions and deuterated hinokitiol was obtained with excellent deuteration efficiencies and in moderate yield. The 1H and 2H NMR spectra indicated that all ring- and aliphatic hydrogens except that on C-6 were substituted by deuterium. According to the substrate scope and computational chemistry, deuteration on tropolone ring was suggested to proceed via D+-mediated process, and which was supported by the results of the experiment with trifluoroacetic acid and Pd(TPP)4. On the other hand, the deuteration on aliphatic group was predicted to be catalyzed by Pd(II) species.

Kinetics of the reaction of H2 with Pt0-nanoparticles in aqueous suspensions monitored by the catalytic reduction of PW12O403−

The mechanism of the reaction between Pt⁰ nanoparticles and Hydrogen was measured in the absence of an electric field via following the formation of PW₁₂O₄₀^4−/5−.

Palladium-catalyzed directed synthesis of ortho-deuterated phenylacetic acid and analogues

The synthesis of deuterium-labeled organic compounds is of increased interest, especially after the approval of deutetrabenazine by the Food and Drug Administration in 2014. The selective incorporation of deuterium in the place of hydrogen not only represents uniqueness in terms of a novel chemical class, but it also can improve the pharmacokinetic profiles of drug molecules while retaining potency and other parameters; thus, hydrogen-deuterium (H/D) exchange methods have been proven to be powerful additions in different areas of chemical science. In that regard, metal-catalyzed deuterium labeling via C-H activation mediated by a unique inbuilt directing group (DG) can play a significant role in the synthesis of novel deuterated chemical entities. In this context, herein, we divulge our results relating to Pd(ii)-catalyzed deuterium incorporation (>97%) at the γ C(sp2)-position of pyridone-containing phenylacetic acid derivatives, where 3-amino-1-methyl-1H-pyridin-2-one (AMP) not only acts as an efficient N,O-directing group, but it also constitutes a part of the target molecules of medicinal importance. Our methodology, which has been optimized based on the effects of temperature, catalyst, time, and substrate scope, shows advantages over existing protocols, with non-selectivity or meager deuteration or the use of an expensive metal (catalytic or super stoichiometric) and a deuterated solvent, reported previously for the deuteration of phenylacetic acid and its derivatives. Moreover, towards our aim of synthesizing deuterium-labeled biologically relevant compounds, the gram scale synthesis of a deuterated analogue of biphenyl acetic acid (3), known to have activity against epileptic seizures, has also been successfully accomplished in high yields and with excellent isotope enrichment via implementing this protocol.

Hydroquinone and benzoquinone-catalyzed aqueous Knoevenagel condensation

A Knoevenagel condensation of various aldehydes with malononitrile effectively proceeded in the presence of hydroquinone/benzoquinone mixed catalysts at room temperature in H₂O. Furthermore, γ-deuterium-labeled α,β-unsaturated nitrile derivatives were also constructed via a deuteration of an aliphatic aldehyde in D₂O using a basic resin and the subsequent Knoevenagel condensation.

Highlights of C (sp2 )-H hydrogen isotope exchange reactions

The highlights of C (sp2 )-H hydrogen isotope exchange (HIE) methods developed over the past 10 years are summarized in this review. Major developments include improved Ir(I) catalysts with greater functional group and solvent compatibility and the development of novel base metal catalysts for HIE. In addition, a number of novel Ru-based catalysts have been developed with promising activity. In the area of Pt- and Pd-catalysed exchange, in addition to new advances on heterogeneous Pt- and Pd-catalysed HIE by Sajiki and Shevchenko, a number of groups have reported on homogenous catalysts of Pt and Pd that show an interesting activity and selectivity.

Silver-catalyzed regioselective deuteration of (hetero)arenes and α-deuteration of 2-alkyl azaarenes

A simple silver-catalyzed regioselective deuteration of (hetero)arenes and α-deuteration of 2-alkyl azaarenes has been described. This strategy provides an efficient and practical avenue to access various deuterated electron-rich arenes, azaarenes and α-deuterated 2-alkyl azaarenes with good to excellent deuterium incorporation utilizing D₂O as the source of deuterium atoms.

A practical silver-catalyzed regioselective deuteration of (hetero)arenes and α-deuteration of 2-alkyl azaarenes utilizing D₂O as a deuterium source has been developed.

Birch-Type Reduction of Arenes in 2-Propanol Catalyzed by Zero-Valent Iron and Platinum on Carbon

Catalytic arene reduction was effectively realized by heating in 2-propanol/water in the presence of Pt on carbon (Pt/C) and metallic Fe. 2-Propanol acted as a hydrogen source, obviating the need for flammable (and hence, dangerous and hard-to-handle) hydrogen gas, while metallic Fe acted as an essential co-catalyst to promote reduction. The chemical states of Pt and Fe in the reaction mixture were determined by X-ray absorption near-edge structure analysis, and the obtained results were used to suggest a plausible reaction mechanism, implying that catalytic reduction involved Pt- and Fe-mediated single-electron transfer and the dehydrogenation of 2-propanol.