Tag: Japan

Scientists from Tokyo University of Science uncover a pivotal enzyme, XccOpgD, and its critical role in synthesizing CβG16α, a key compound used by Xanthomonas pathogens to enhance their virulence against plants. This breakthrough opens new avenues for developing targeted pesticides that combat plant diseases without harming beneficial organisms. Insights into XccOpgD’s enzymatic mechanism and optimal conditions offer promising prospects for sustainable agriculture, bolstering crop resilience and global food security while minimizing environmental impact.

Plant diseases pose significant challenges to agricultural productivity, presenting formidable hurdles that require urgent attention. Left unchecked, these diseases can spread rapidly, inflicting widespread damage on crops and leading to reduced yields and substantial economic losses. Therefore, accurately identifying the pathogens responsible for these diseases is crucial. This identification allows for targeted interventions that minimize risks and effectively mitigate the agricultural impacts.

Xanthomonas species are notorious plant pathogens that affect a broad spectrum of hosts, including key crops like rice, wheat, and tomatoes. These pathogens augment their pathogenicity by utilizing α-1,6-cyclized β-1,2-glucohexadecaose (CβG16α) to suppress essential plant defense mechanisms, such as the expression of pathogenesis-related proteins and the accumulation of callose.

In a recent breakthrough published on June 19, 2024, in the Journal of the American Chemical Society, a team of researchers led by Associate Professor Masahiro Nakajima from Tokyo University of Science unveiled a significant discovery. They identified XccOpgD, a glycoside hydrolase (GH186) found in X. campestris pv campestris which plays a pivotal role in the biosynthesis of CβG16α. The research team also included Mr. Sei Motouchi from Tokyo University of Science, Principal Scientist Shiro Komba from the Institute of Food Research, NARO, and Hiroyuki Nakai from Niigata University.

“Glycan structures are intricate and multifaceted and fulfill diverse crucial roles in nature and organisms. Enzymes synthesize and degrade glycans, exhibiting diverse structures and functions that correspond to the glycan diversity. However, our understanding of these enzymes is still limited, which drives the search for new enzymes with varied new potentials,” explains Prof. Nakajima, elaborating on the study’s rationale.

The team conducted biochemical analysis to elucidate the role of XccOpgD in CβG16α biosynthesis. Advanced techniques such as X-ray crystallography were employed as structural analysis to unravel the enzyme’s catalytic mechanism and substrate specificity.

These efforts have yielded profound insights. XccOpgD belongs to the GH186 family, essential for regulating bacterial cell wall components. Unlike the first identified GH186 enzymes, XccOpgD exhibits an unprecedented enzymatic mechanism known as anomer-inverting transglycosylation.

“Reactions of typical GH enzymes are classified into four types by combination of retaining or inverting, and reaction with water (hydrolysis) or sugar (transglycosylation) theoretically. However, one classification is missing somehow in a long history of researches on carbohydrate associated enzymes and we discovered the missing classification. This breakthrough was made possible by unique structural environment, opening new possibilities for enzyme-based glycosylation,” explains Prof. Nakajima. Moreover, the sugar chains synthesized through this mechanism are not merely minor components but rather essential structures utilized by various Gram-negative bacteria in nature for pathogenic purposes.

Detailed studies revealed that linear β-1,2-glucan was converted to cyclic compound and the compound was identified as CβG16α using nuclear magnetic resonance. Structural analysis of the Michaelis complex identified crucial substrate binding residues, further elucidating specific interactions along the glucan chain. Notably, XccOpgD utilizes an anomer-inverting transglycosylation mechanism, with D379 and D291 playing pivotal roles as catalysts.

These findings deepen our understanding and open avenues for developing targeted strategies against Xanthomonas-induced plant diseases. “We are expecting a pesticide concept targeting this enzyme homolog in the future. Unlike fungicides that promote the emergence of drug-resistant bacteria in soil, targeting this enzyme could potentially inhibit pathogenicity without causing sterilization. Enzyme homologs identified in this study may serve as promising structure-based drug targets, offering a potential solution to the issue of drug-resistant bacteria,” says a hopeful Prof. Nakajima.

The discovery of XccOpgD and its role in CβG16α biosynthesis marks a major breakthrough in agriculture. It promises enhanced resilience and food security while mitigating environmental impacts linked to conventional pesticides. Overall, this advancement offers sustainable solutions to global agricultural challenges, promoting environmental stewardship and economic viability for farmers worldwide.

In a recent breakthrough, researchers at Tokyo University of Science have successfully developed an efficient method to synthesize eutyscoparol A and violaceoid C, two naturally occurring compounds with promising antimalarial and antibacterial properties. The new approach involves the synthesis of these compounds using readily available dinitriles. This method requires fewer steps and produces the bioactive compounds in higher yields compared to previous approaches, opening up new avenues for drug development.

The natural world is rich in chemical compounds with remarkable medicinal properties. A notable example is penicillin, discovered by chance from the Penicillium mold. This discovery revolutionized the treatment of bacterial infections and highlighted the potential of natural compounds in medicine. Since then, the identification, isolation, and synthesis of novel bioactive compounds from plants, fungi, and bacteria have become fundamental to drug development.

Recently, two groups of naturally occurring bioactive compounds have garnered significant attention: violaceoids A–F from the fungus Aspergillus violaceofuscus and eutyscoparols A-G from the fungus Eutypella scoparia. These compounds share similar structures, featuring a 2,3-alkylated quinol moiety and a hydroxymethyl group, and are believed to possess antimalarial and antibacterial properties. Following their initial discovery in 2014 and 2020, scientists have been working to produce these compounds in larger quantities for further study.

In a recent study, researchers from Tokyo University of Science (TUS), led by Associate Professor Takatsugu Murata and Professor Isamu Shiina from the Department of Applied Chemistry, Faculty of Science, have made significant progress by developing an efficient method to synthesize eutyscoparol A and violaceoid C. Their work, featured on the cover of Volume 13, Issue 7 of the Asian Journal of Organic Chemistry, and published on 25 April 2024, could lead to new treatments or drugs.

“Eutyscoparol is a group of compounds whose pharmacological activity had not been thoroughly explored. Our goal was to make this possible through artificial synthesis and support the development of new drugs,” says Dr. Murata.

The researchers used a retrosynthetic analysis to simplify the production process. This approach breaks down complex molecules into simpler, more accessible materials. They used this method to synthesize eutyscoparol A (4) and violaceoid C (3) starting from commercially available dinitriles (6) through violaceoid A (1) intermediates. Dinitriles were chosen because they are easy to obtain and can be converted into aldehydes (5), which are precursors to violaceoid A intermediates. To make the aldehyde (5), dinitrile (6) was first converted into diester. Then, the hydroxy groups in diester were protected with a tert-butyldiphenylsilyl (TBDPS) group to form protected ether. This ether was reduced to form a symmetric diol. One hydroxy group in diol was then selectively protected to create desymmetrized tetrahydropyranyl (THP)-ether, which was oxidized to produce the aldehyde.

With the aldehyde prepared, the researchers proceeded to synthesize violaceoid A (1) and rac-violaceoid B (2) intermediates through a series of reactions. To prepare violaceoid A (1), the aldehyde was first alkylated to form an intermediate, which was then converted to olefin using mesylation or the Julia–Kocienski reagent. The THP-protecting group in olefin was removed with isopropyl alcohol to produce alcohol. Finally, two TBDPS groups were removed from the alcohol to get violaceoid A (1). Rac-violaceoid B (2) was synthesized using similar methods.

These improvements made the process much more efficient. The researchers synthesized violaceoid A (1) in 8 steps with a 33% yield, compared to the previous 10-step process that had only an 11% yield. Similarly, they prepared rac-violaceoid B (rac-2) in 8 steps with a 35% yield, improving on the earlier 9-step process with a 15% yield.

After successfully synthesizing the intermediates, the researchers moved on to produce violaceoid C (3) and eutyscoparol A (4). The synthesis of violaceoid C (3) was relatively straightforward, involving the hydrogenation of the double bond in violaceoid A (1) to yield violaceoid C (3) with high efficiency. For eutyscoparol A (4), the researchers selectively methylated two of the three hydroxy groups in violaceoid A (1) by refluxing the reaction mixture with potassium carbonate and iodomethane. Overall, violaceoid C (3) was synthesized in nine steps with a 30% yield, and eutyscoparol A (4) in nine steps with a 28% yield.

With improved yields and simpler synthesis steps, the proposed approach makes it easier to produce these compounds on a larger scale and could lead to further research into their potential therapeutic properties. “The synthesis of violaceoid A and eutyscoparol C on a subgram scale will help us study their pharmacological effects, which we expect to include cytotoxic, antibacterial, and antimalarial activities,” concludes Prof. Shiina.

The photoisomerization of E-to-Z alkenes has many applications in diverse fields, including organic chemistry, polymer chemistry, and medicinal chemistry. In a new study, researchers from Japan developed a new closed-loop method for photoisomerization of E-to-Z alkenes using a recycling photoreactor. This innovative method utilizes the high-performance liquid chromatography method to recycle the samples, thereby improving efficiency. This eco-friendly method can lead to the sustainable development of various chemicals, including pharmaceuticals.

Z-alkenes are organic compounds with a double bond between two carbon atoms and two substituents attached to the carbon atoms on the same side of the double bond. They are ubiquitous structural components of organic compounds in chemistry and biology. It is well known that many of the Z-alkenes cannot be prepared through conventional methods involving thermodynamic methods while photoisomerization can offer good yields. Photoisomerization is a process in which the structural arrangement of an isomer of a molecule is changed to another isomer by absorption of light. The photoisomerization of E-alkenes to produce Z-alkenes has many applications in the fields of organic chemistry, polymer chemistry, and medicinal chemistry.

Many studies have explored different methods for photoisomerization of E-to-Z alkenes. A notable approach involved a continuous-flow system, in which the photosensitizer was immobilized in an ionic liquid and continuously recycled via a simple phase separation process. Photosensitizers are materials that enhance the rate of photoisomerization reactions by absorbing light energy and transferring it to the reactant molecule. However, current methods based on the use of ionic liquids are time-consuming and difficult to apply to recycling high-performance liquid chromatography (HPLC) technology, which enables the recycling of samples and therefore can enhance the efficiency of photoisomerization.

Inspired by these findings, in a new study, a team of researchers from Japan, led by Professor Hideyo Takahashi from the Faculty of Pharmaceutical Sciences at Tokyo University of Science, explored the photoisomerization of E-cinnamamides to Z-cinnamamides using a recycling photoreactor coupled with an HPLC system. The study, published online in The Journal of Organic Chemistry on June 05, 2024, included contributions from Ms. Mayuko Suga, Ms. Saki Fukushima, and Assistant Professor Dr. Kayo Nakamura, also from Tokyo University of Science.

The team had previously developed a recycling photoreactor based on the deracemization concept. Prof. Takahashi explains, “Our closed-loop recycling photoreactor was initially used to convert a racemate, a mixture of left and right-handed enantiomers of a chiral molecule, into the pure desired enantiomer. It consists of a photocatalyst immobilized on a resin, which converts an undesired enantiomer into a racemate, and an HPLC column which separates the desired enantiomer. In this study, we adapted this method to convert E-cinnamamides to their Z-isomers.”
To employ this method for E-to-Z photoisomerization of alkenes, a photosensitizer that promotes rapid photoisomerization is required. To this end, the researchers screened several commercially available photosensitizers and identified thioxanthone as the best candidate. Next, they investigated its immobilization. Thioxanthone, with functional amide groups as linkages, was immobilized on a modified silica gel. This immobilization not only prevented the leakage of photosensitizer in the solid phase but also enhanced the catalytic activity compared to the parent soluble thioxanthone. This enhancement was particularly interesting, as solid-phase reactions are typically slower than liquid-phase reactions.

This superior catalytic activity was attributed to the introduction of suitable functional groups. The researchers, therefore, evaluated the catalytic activity of various photosensitizers with different functional groups by comparing the total amount of light required for promoting photoisomerization. With the optimal photosensitizer identified, they conducted the photoisomerization reactions in the recycling photoreactor, yielding the desired Z-alkenes in good yields after 4–10 cycles.

“This recycling photoreactor shows promise as an efficient alternative system to produce Z-alkenes,” remarks Prof. Takahashi. “Due to the continuous closed-loop recycling of the samples, it represents an environmentally friendly and sustainable method.”

This innovative method can lead to more eco-friendly development of Z-alkenes, and therefore pharmaceuticals, paving the way towards a sustainable future.

The anti-Michael addition reaction, which involves nucleophilic addition reactions to the α-position of α,β-unsaturated carbonyl compounds, has been difficult to achieve so far. In a new study, researchers from Japan have developed a new method for successful anti-Michael addition reaction of α-unsaturated carbonyl compounds, which are commonly used in pharmaceuticals. This reaction is expected to be used as a one-step synthesis method with 100% atomic efficiency for α-unsaturated carbonyl compounds.

In 1887, chemist Sir Arthur Michael reported a nucleophilic addition reaction to the β-position of α,β- unsaturated carbonyl compounds. These reactions, named Michael addition reactions, have been extensively studied to date. In contrast, the anti-Michael addition reaction, referring to the nucleophilic addition reaction to the α-position, has been difficult to achieve. This is due to the higher electrophilicity of the β-position compared to the α-position. Previous attempts to overcome these difficulties have involved two main methods. The first is restricting the addition position via intramolecular reactions, while the second method involves introducing a strong-electron withdrawing group at the β-position. However, these methods are not ideal for synthesizing complex molecules via the anti-Michael reaction.

In a new study, a global team of researchers, led by Professor Takanori Matsuda and including Mr. Ryota Moro, both from the Department of Applied Chemistry at Tokyo University of Science, Japan, as well as including Assistant Professor Hirotsugu Suzuki from the Tenure-Track Program for Innovative Research at the University of Fukui, Japan, successfully achieved palladium-catalyzed anti-Michael addition reaction of acrylamides. This represents the first example of an anti-Michael-type addition reaction. “We found that the presence of a catalytic amount of palladium(II) trifluoroacetate Pd(TFA)2 is capable of facilitating the anti-Michael addition of indole to acrylamide with an aminoquinoline group as a directing group, producing the addition product in high-yield,” explains Prof. Matsuda.

Their study was made available online on May 14, 2024, and published in Volume 146, Issue 20 of the Journal of the American Chemical Society on May 22, 2024.

The team reasoned introducing a directing group into an α,β-unsaturated carbonyl compound could facilitate an anti-Michael type addition reaction by stabilizing the reaction intermediate. To test this, the researchers first used an acrylamide having an aminoquinoline-directing group, and a nucleophile, 1-methylindole, as model substrates to investigate the anti-Michael type addition reaction in the presence of the palladium catalyst. This reaction produced the desired product with a 90% yield. At a reaction scale of two millimoles, there was no yield loss, signifying the practicality of the reaction.

This reaction was also carried out with β-substituted cinnamamide derivatives and crotonamide derivatives with an alkyl group. Moreover, the reaction proceeded smoothly with a wide range of nucleophiles, including many indoles, heterocyclic compounds such as pyrroles and thiophenes, and electron-rich aromatic compounds. Additionally, the aminoquinoline-directing group used in this reaction can be converted to carboxylic acids and other amides, signifying the usefulness of the reaction.

The researchers also investigated the mechanism for this reaction through labeling experiments. They found that initially, the acrylamide coordinates to Pd(TFA)2 to form a five-membered ring palladacyle intermediate. The reaction then proceeds with the nucleophilic attack by indole on the intermediate, producing alkylpalladium species. Finally, an acid removes palladium and regenerates Pd(TFA)2, producing the desired α-substituted carbonyl compound.

Highlighting the potential applications of this study, Dr. Suzuki says, “The anti-Michael type addition is expected to become an ideal one-step reaction with 100% atomic efficiency for the synthesis of α-substituted carbonyl compounds, which are often used in pharmaceuticals. Our method will enable the widespread application of this reaction.”

Overall, this novel method can lead to efficient and sustainable synthesis of α-substituted carbonyl compounds and consequently pharmaceuticals, among other organic compounds.

Doxepin is an antihistaminic, antidepressant, and sleeping aid that has two geometric isomers—molecules with equal chemical formulas but different 3D arrangements. While its Z-isomer is known to be more effective than its E-isomer, the precise nature of its binding to the histamine H1 receptor remained elusive. Now, in a recent study, researchers from Japan thoroughly addressed this knowledge gap through an innovative experimental protocol, paving the way to next-generation antihistamines with fewer side effects.

Even if two molecules have the exact same chemical formula and the same number and types of bonds, their three-dimensional arrangements can still be different. While some people might mistakenly disregard this as a minor detail, even simple changes in the position or orientation of a functional group can dramatically affect the biological properties of a molecule, sometimes rendering an otherwise benign substance into a highly toxic one. Thus, the study of such possible molecular variants, called ‘geometric isomers,’ is essential in the field of drug development.

Doxepin stands out as a notable example of a drug that is commercialized as a mixture of two geometric isomers, namely the E- and Z-isomers. Both doxepin isomers bind to histamine H1 receptor (H1R), which is expressed throughout the central nervous system, smooth muscle cells, and vascular endothelial cells. Besides its use as an antihistaminic drug, doxepin is also typically used as an antidepressant and sleeping aid. While biological tests in animals have shown that the Z-isomer is more effective than the E-isomer, the differences in affinity to H1R between the E- and Z-isomers are unknown. Moreover, the specifics of how these compounds actually bind to H1R remain elusive.

Against this backdrop, a research team from Tokyo University of Science, Japan, set out to clarify the finer details of the interactions between doxepin isomers and H1R. Their latest paper, which was published on June 25, 2024, in the Journal of Molecular Recognition, was co-authored by Professor Mitsunori Shiroishi, Mr. Hiroto Kaneko, and Associate Professor Tadashi Ando, among others. This study is a follow-up to past work done by Prof. Shiroishi and colleagues. “We previously revealed the crystal structure of the complex formed by H1R and doxepin, but we were unable to determine which isomer was bound,” he explains, “We then came up with a method to determine the binding affinity of the isomers, and thus carried out this study.”

To achieve this challenging goal, the researchers first produced a customized yeast expression vector by strategically inserting the H1R gene into it. This vector was used to modify yeast cultures so that they produce H1R. After retrieving the membranes from these cells, they applied a solution containing commercial doxepin, producing H1R-doxepin complexes. Following extraction and purification of these complexes, they removed any excess (unbound) doxepin. Finally, by denaturing the H1R receptors, they could free the bound doxepin molecules and measure their numbers in a high-performance liquid chromatography setup.

Using this protocol, the researchers could accurately quantify the amount of each isomer that was bound to the extracted receptors, which is directly tied to their relative binding affinity. They found that the affinity to H1R of the Z-isomer was over five times higher than that of the E-isomer.

The team then delved deeper into the nature of how doxepin isomers bind to H1R. Through experiments on a mutant variant of H1R coupled with molecular dynamics simulations, they revealed that the Thr112 side chain in the ligand-binding pocket of H1R creates a chemical environment that enhances selectivity for the Z-isomer.

Taken together, the findings of this study shed light on how a widely used small molecule drug interacts with an important cellular receptor. “Our efforts could serve as the basis for designing next-generation antihistamines that are more effective and have fewer side effects,” highlights Prof. Shiroishi, “Worth noting, this newfound knowledge will be useful for designing compounds that bind not only to H1R, but also other disease-relevant target proteins.”

The rational design of future drugs, aided and validated by computational techniques like molecular dynamics simulations, could usher in a new era in medicine. More specifically, by understanding the binding properties of isomers in detail, many small-molecule drugs could be made more effective, safer, and better suited for targeted therapies.

Let us hope this vision of the future becomes a reality soon!

Solid oxide fuel cells (SOFCs) are a promising avenue to meet global demands for clean energy. They can produce electricity through environmentally friendly electrochemical reactions. However, existing SOFCs operate at high temperatures, which lowers their efficiency. Now, researchers from Japan have developed a novel perovskite-based anode material for SOFCs that exhibits mixed hole–proton conduction at medium-range temperatures. Their findings will help establish more efficient energy technologies, leading the way to more sustainable societies.

Amidst the ongoing energy and climate crises, the stakes have never been higher. We are pressed for time to find better ways of producing clean energy to replace fossil fuels. Thus far, fuel cells appear to be one of the most promising research directions. These electrochemical devices can produce electricity directly from chemical reactions, which can be tailored to be environmentally friendly in terms of their reactants and outputs.

Various types of fuel cells exist, but solid oxide fuel cells (SOFCs) have attracted special attention from researchers. By operating without the need for a liquid electrolyte, they offer higher safety and are often easier to manufacture. Unfortunately, one of their main drawbacks is their high operating temperature. Conventional SOFCs need to be at over 700 °C to work properly, which limits their applicability, reduces their efficiency and power output, and often compromises their durability. Thus, proton-conducting SOFCs (PC-SOFCs), which can operate within a lower temperature range, are being investigated as a promising alternative.

Against this backdrop, a research team including Professor Tohru Higuchi from Tokyo University of Science has achieved a breakthrough in PC-SOFCs by developing a novel hole–proton mixed-conductor material. Their findings, which have been published in the Journal of the Physical Society of Japan on June 18, 2024, could pave the way for important technological advancements in energy technologies.

The material in question is a perovskite-type oxide ceramic with the formula BaCe0.4Pr0.4Y0.2O3−δ (BCPY). These particular dopants, namely Pr and Y ions, were selected based on previous works by members of the research team. They observed that BaCe0.9Y0.1O3−δ and BaPrO3−δ exhibited proton and hole (a type of positive charge carrier) conduction, respectively. Thus, they theorized that co-doping with both Pr and Y might lead to high proton–hole mixed conductivity.

Such a material could be used in the anode electrode of PC-SOFCs, as Prof. Higuchi explains: “The Pt metal electrode used in other fuel cells has issues, such as a large drop in power output because electrochemical reactions occur only at the three-phase interface where the fuel gas/electrode/electrolyte intersect. To solve this issue, a dense membrane with mixed conduction could be useful for improving the performance of PC-SOFC by expanding the electrochemical reaction area.”

Using a sputtering technique, the researchers produced thin films of BCPY and carefully analyzed its conduction properties, seeking to find evidence of mixed proton–hole conduction. To this end, they established a quantitative evaluation method to determine oxygen vacancies using X-ray absorption spectroscopy and defect chemistry analysis. Through these and several additional experiments, including synchrotron radiation photoelectron spectroscopy for electronic band structure analysis, they found substantial evidence that mixed hole–proton conductivity can occur on the surface of the proposed electrode material.

Notably, BCPY electrodes exhibited a high conductivity of over 10−2 S.K/cm at 300 °C, which outlines a bright future not only for PC-SOFCs, but for other technologies as well. “If we can further confirm that BCPY thin films do enable hole–proton mixed conductivity, BCPY may become a novel oxide material for not only PC-SOFC anode electrode membranes but also electric-double-layer-transistors,” highlights Prof. Higuchi. To clarify, this transistor technology can address the scalability and miniaturization problems of conventional transistors, which will be crucial to developing artificial intelligence systems and increasing the computational capacity of personal electronic devices.

In any case, this study sheds some much-needed light on new electrode materials for PC-SOFCs. With further advances in this exciting field, electrochemical energy generation could eventually enable us to power up our homes and cars with cleaner electricity, paving the way to more sustainable societies.

Nanoscale electron transfer (ET) in solids is fundamental to the development of multifunctional materials. However, ET in solids is not yet clearly understood. Now, researchers from Japan achieved a direct observation of solid-state ET through X-ray crystal analysis by fabricating a novel double-walled non-covalent crystalline nanotube, which can absorb electron donor molecules and maintain its crystalline structure during ET. This innovative approach can lead to the design of novel functional materials soon.

Electron transfer (ET) is a process in which an electron is transferred from one atom or molecule to another. ET is fundamental to electrochemical reactions with applications in many fields. Nanoscale ET, which involves the transfer of electrons in the range of 1–100 nanometers in solids is fundamental to the design of multifunctional materials. However, this process is not yet clearly understood.

Nanotubes, nanomaterials with unique cylindrical nanostructures, offer a variety of ET properties that can be realized through electron and hole (vacant spaces left by electrons) injections into the nanotubes, making them a suitable candidate for studying nanoscale ET. Although carbon-based nanotubes have fascinating ET properties, they are particularly difficult to control in terms of their shape and size due to extreme conditions, such as high temperatures, required for their synthesis. A viable approach for fabricating well-defined tunable nanotubes is bottom-up fabrication of non-covalent nanotubes, which sometimes result in crystalline-form nanotubes. Non-covalent nanotubes are formed through the inherent attractive interactions or non-covalent interactions between atoms, instead of the strong covalent interactions seen in carbon nanotubes. However, they are not strong enough to endure electron and hole injections, which can break their non-covalent interactions and destroy their crystalline structure.

In a recent study, a team of researchers from the Department of Applied Chemistry at Tokyo University of Science, led by Professor Junpei Yuasa and including Dr. Daiji Ogata, Mr. Shota Koide, and Mr. Hiroyuki Kishi, used a novel approach to directly observe solid-state ET. Prof. Yuasa explains, “We have developed crystalline nanotubes with a special double-walled structure. By incorporating electron donor molecules into the pores of these crystalline nanotubes through a solid-state oxidation reaction, we succeeded in directly observing the electron transfer reaction in the solid using X-ray crystal structure analysis.” Their findings were published in the journal Nature Communications on May 23, 2024.

The researchers used a novel supramolecular crystallization method, which involves oxidation-based crystallization, to fabricate zinc-based double-walled crystalline nanotubes. This double-walled structure with large windows in the nano-tube walls makes the crystal robust and flexible enough to maintain its crystalline state when subjected to ET oxidation processes. Moreover, this structure allows the crystal to absorb electron donor molecules. The researchers used ferrocene and tetrathiafulvalene as electron donor molecules, which were absorbed through the windows of the nanotube crystals. This allows electrons to be removed from the absorbed electron donors through solid-state ET oxidation reactions, resulting in the accumulation of holes in the donors inside the nanotube. Due to the robustness of the crystals, the researchers were able to observe this ET oxidation process using X-ray crystal structure analysis directly, uncovering key insights.

This novel approach is highly valuable for direct observation of ET in solid nanomaterials. Highlighting the potential applications of this study, Prof. Yuasa says, “Understanding ET can lead to the development of novel functional materials, which in turn can lead to the design of more efficient semiconductors, transistors, and other electronic devices. Optoelectronic devices, such as solar cells, rely heavily on ET. Hence, direct observation of ET can help improve these devices’ performance. Additionally, this approach can lead to advancements in energy storage, nanotechnology, and materials science research.”

Overall, this study is a striking example of direct observation of solid-state ET, which can be expanded to observe ET and related phenomena in other nanomaterials.

Obesity and inflammatory diseases are increasing in prevalence and contribute to the growing burden of lifestyle disorders such as diabetes and hypertension. There is a lack of naturally derived alternatives to tackle these issues. Researchers from Tokyo University of Science have synthesized novel amino acid derivatives of menthol and studied its properties. The menthyl esters showed exceptional anti-inflammatory and anti-obesity activities during preclinical studies and can be developed as therapeutic compounds with further research.

Modified derivatives of natural products have led to significant therapeutic advances and commercial success in recent times. Menthol is a naturally occurring cyclic monoterpene alcohol found in various plants, particularly in members of the mint family such as peppermint and spearmint. It is a common ingredient found in a wide range of confectionaries, chewing gums and oral care products. Interestingly, menthol also has high medicinal value due to its analgesic, anti-inflammatory, and anti-cancer effects.

In a recent study, a team of researchers led by Professor Gen-ichiro Arimura from the Department of Biological Science and Technology, Tokyo University of Science, Japan, developed and investigated menthyl esters of valine (MV) and isoleucine (MI), which are derived from menthol by replacing its hydroxyl group with valine and isoleucine, respectively.

Their research findings were published in the Immunology journal on May 08, 2024. Sharing the motivation behind the present work, Prof. Arimura says, “The functional components of plants that contribute to human health have always intrigued me. Discovering new molecules from natural materials inspired our research team to develop these amino acid derivatives of menthol.”

The researchers began by synthesizing menthyl esters of six amino acids characterized by less-reactive side chains. Subsequently, they assessed the properties of these esters using in vitro cell line studies. Finally, they conducted experiments in mice to explore the effects of these compounds under induced disease conditions. The exceptional anti-inflammatory profiles of MV and MI was determined by assessing the transcript levels of tumor necrosis factor-α (Tnf) in stimulated macrophage cells. Remarkably, both MV and MI outperformed menthol in the anti-inflammatory assay. RNA sequencing analysis revealed that 18 genes involved in inflammatory and immune responses were effectively suppressed.

Elated with their findings, the researchers went a step further and investigated the mechanism of action of the menthyl esters. They discovered that liver X receptor (LXR) – an intracellular nuclear receptor, had an important role in the anti-inflammatory effects and this was independent of the cold-sensitive transient receptor TRPM8, which primarily detects menthol. Delving deeper into the LXR-dependant activation of MV and MI, they found that Scd1 gene – central to lipid metabolism was upregulated by LXR. Moreover, in mice with induced intestinal colitis, the anti-inflammatory effects were further validated with suppressed transcript levels of Tnf and Il6 genes by MV or MI, in an LXR-dependent manner.

Driven by the discovery of LXR-SCD1 intracellular machinery, Prof. Arimura and his team hypothesized the menthyl esters to possess anti-obesity properties. They found that these esters inhibited adipogenesis-fat accumulation, specifically at the mitotic clonal expansion stage in 3T3-L1 adipocyte cells. During animal studies, the diet-induced obesity in mice was ameliorated and adipogenesis was suppressed.

Menthyl esters possess unique advantages compared to other anti-inflammatory or anti-obesity compounds currently being researched or used. Their specific mechanisms of action, that contribute to their dual anti-inflammatory and anti-obesity effects sets them apart from other compounds and may make them particularly effective in addressing both inflammatory conditions and metabolic disorders. They could benefit specific populations like individuals with chronic inflammatory conditions, metabolic syndrome, or obesity-related complications.

“Although this study focused on their functions and mechanisms of action in diseases modeled after inflammation and obesity, we expect that these compounds will also be effective against a wide range of lifestyle-related diseases caused by metabolic syndrome, such as diabetes and hypertension, as well as allergic symptoms,” says Prof. Arimura optimistically.

In conclusion, this study underscores the importance and value of multi-faceted molecules derived from naturally occurring substances. Future research involving these novel and superior menthyl esters may result in therapeutic compounds to tackle the ever-growing health concerns of obesity and inflammatory conditions.