Royal Society of Chemistry (RSC) Acta Medica Okayama 1463-9262 27 18 2025 Deoxygenative dual CO2 conversions: methylenation and switchable N-formylation/N-methylation of tryptamines 5359 5365 EN Kazuto Takaishi Division of Applied Chemistry, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Hajime Morishita Division of Applied Chemistry, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Kosuke Iwaki Division of Applied Chemistry, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Environmental, Life, Natural Science and Technology, Okayama University The unprecedented one-pot synthesis of N-formyl/N-methyltryptolines from tryptamines was achieved via phenylsilane-assisted deoxygenative dual CO2 conversions. Two CO2 molecules acted as different synthons and were converted into methylene and N-formyl/N-methyl groups. The CO2 reduction step was catalyzed by a pentanuclear zinc complex at atmospheric pressure under solvent-free conditions. The N-formyl/N-methyl products could be switched by changing the amount of phenylsilane, and the amounts of in situ generated bis(silyl)acetals and silyl formates were key to the chemoselectivity. Methylenation, N-formylation, and N-methylation proceeded via the Pictet–Spengler reaction, amine–acid condensation, and the Eschweiler–Clarke reaction, respectively. The CO2 reduction with phenylsilane could also be applied to the one-pot three-step synthesis of spiro[oxindole-pyrrolidine]s. No potential conflict of interest relevant to this article was reported.

American Chemical Society (ACS) Acta Medica Okayama 0024-9297 58 3 2025 Synthesis and Postfunctionalization of Acrylate-Appended Poly(cyclohexene carbonate)s: Modulation of Properties of CO2-Based Polymers 1571 1577 EN Chihiro Maeda Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Hina Inoue Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Functional CO2-based polycarbonates are expected to be sustainable materials. Herein, a bifunctional aluminum porphyrin catalyzed the terpolymerization of cyclohexene oxide (CHO), acrylate-appended CHO, and CO2 to provide poly(cyclohexene carbonate)s (PCHCs) with acrylate groups. Postfunctionalization of PCHCs via Michael addition or Heck reaction enabled the incorporation of thiol, amine, and aromatics into PCHCs with high selectivity and efficiency. PCHCs with the flexible long alkyl chains showed a glass-transition temperature (Tg) of down to 52 °C, which was much lower than that of PCHC (127 °C). In sharp contrast, PCHCs with rigid pyrenyl groups showed Tg values of up to 152 °C and fluorescence emission. Thus, a wide range of polymers were obtained by robust and sustainable synthetic methods, and the functional groups modulated the properties of the CO2-based polycarbonates. No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry (RSC) Acta Medica Okayama 1359-7345 61 25 2025 Recent development of azahelicenes showing circularly polarized luminescence 4757 4773 EN Chihiro Maeda Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Recently, a variety of circularly polarized luminescence (CPL) dyes have been developed as next-generation chiroptical materials. Helicenes, ortho-fused aromatics, have been recognized as some of the most promising CPL dyes. Although typical carbohelicenes show CPL, weak fluorescence is often emitted in the blue region. In contrast, heteroatom-embedded helicenes (heterohelicenes) can show intense fluorescence and CPL in the visible region because heteroatoms alter the electronic states of helicene frameworks. Among various heterohelicenes, nitrogen-embedded helicenes (azahelicenes) have unique features such as facile functionalization and sensitive responses to acid/base or metal ions. Furthermore, polycyclic aromatic hydrocarbons (PAHs) containing azaborine units have been recognized as excellent luminescent materials, and the helical derivatives, B,N-embedded helicenes, have been rapidly growing recently. In this feature article, we review and summarize the synthesis and chiroptical properties of azahelicenes, which are classified into imine-type and amine-type azahelicenes and B,N-embedded helicenes. CPL switching systems of azahelicenes are also reviewed. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 1433-7851 64 8 2025 B,N‐Embedded Helical Nanographenes Showing an Ion‐Triggered Chiroptical Switching Function e202418546 EN Chihiro Maeda Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Sayaka Michishita Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Issa Yasutomo Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Intramolecular oxidative aromatic coupling of 3,6-bis(m-terphenyl-2’-yl)carbazole provided a bis(m-terphenyl)-fused carbazole, while that of 3,6-bis(m-terphenyl-2’-yl)-1,8-diphenylcarbazole afforded a bis(quaterphenyl)-fused carbazole. Borylation of the latter furnished a B,N-embedded helical nanographene binding a fluoride anion via a structural change from the three-coordinate boron to the four-coordinate boron. The anionic charge derived from the fluoride anion is stabilized over the expanded π-framework, which leads to the high binding constant (Ka) of 1×105 M−1. The four-coordinate boron species was converted back to the parent three-coordinate boron species with Ag+, and the chiroptical switch between the three-coordinate boron and four-coordinate boron species has been achieved via the ion recognition with the change in the color and glum values. No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry (RSC) Acta Medica Okayama 1359-7345 61 1 2025 Terpolymerization reactions of epoxides, CO2, and the third monomers toward sustainable CO2-based polymers with controllable chemical and physical properties 46 60 EN Koichi Nakaoka Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Carbon dioxide (CO2) serves as a cheap, abundant, and renewable C1 building block for the synthesis of organic compounds and polymers. Selective and efficient CO2 fixation processes are still challenging because of the kinetic and thermodynamic stability of CO2. Among various CO2 fixation processes, the ring-opening copolymerization (ROCOP) of epoxides and CO2 gives aliphatic polycarbonates with high atom economy, although the chemical and physical properties of the resulting polycarbonates are not necessarily satisfactory. Introducing the third monomers into this ROCOP system provides new terpolymers, and the thermal, optical, mechanical or degradation properties can be added or tuned by incorporating new polymer backbones derived from the third monomers at the expense of the CO2 content. Here we review the terpolymerization reactions of epoxides, CO2, and the third monomers such as cyclic anhydrides, lactones, lactides, heteroallenes, and olefins. The development of catalysts and the control of the polymer structures are described together with the chemical and physical properties of the resulting polymers. No potential conflict of interest relevant to this article was reported.

American Chemical Society (ACS) Acta Medica Okayama 0002-7863 146 22 2024 Skeletal Formation of Carbocycles with CO2: Selective Synthesis of Indolo[3,2-b]carbazoles or Cyclophanes from Indoles, CO2, and Phenylsilane 14935 14941 EN Sha Li Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Shoko Nakahara Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Taishin Adachi Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Takumi Murata Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Kazuto Takaishi Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University The catalytic reactions of indoles with CO2 and phenylsilane afforded indolo[3,2-b]carbazoles, where the fused benzene ring was constructed by forming two C–H bonds and four C–C bonds with two CO2 molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO2 molecules were also obtained, where the cyclophane framework was constructed by forming six C–H bonds and six C–C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate. No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry (RSC) Acta Medica Okayama 1759-9954 14 37 2023 Catalytic synthesis and physical properties of CO2-based cross-linked poly(cyclohexene carbonate)s 4338 4343 EN Chihiro Maeda Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Kenta Kawabata Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Kaito Niki Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Yuma Sako Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Takumi Okihara Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Bifunctional aluminum porphyrins (0.001 mol%) catalyzed the terpolymerization of cyclohexene oxide (CHO), bis(CHO), and CO2 to give cross-linked polycarbonates (CLPs) under solvent-free conditions. A small amount of bis(CHO) acted as a cross-linking agent, and the use of only 0.1 mol% bis(CHO) to CHO produced polymers of quite large sizes. The thermal and mechanical properties of CLPs could be altered by changing the structure and amount of bis(CHO), and the CLPs showed improved thermal stability and tensile strength as compared to linear poly(cyclohexene carbonate)s (PCHCs). The degradation of the CLPs was also investigated, and the selective cleavage of the cross-links was achieved by UV light irradiation to give linear PCHCs. The present study disclosed the potentials of cross-linking terpolymerization for the preparation of various CLPs with a constant CO2 content (31 wt%). No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry (RSC) Acta Medica Okayama 1759-9954 15 8 2024 Terpolymerizations of cyclohexene oxide, CO2, and isocyanates or isothiocyanates for the synthesis of poly(carbonate–urethane)s or poly(carbonate–thioimidocarbonate)s 707 713 EN Koichi Nakaoka Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Satoshi Muranaka Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Io Yamamoto Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Terpolymerization of cyclohexene oxide (CHO), CO2, and aryl isothiocyanates produced poly(carbonate–thioimidocarbonate)s with gradient character, while that of CHO, CO2, and aryl isocyanates furnished poly(carbonate–urethane)s with random sequences. The former underwent partial degradation upon acid treatment or UV irradiation, while the latter was stable under the same conditions. No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry Acta Medica Okayama 2041-6520 2021 Chiral exciplex dyes showing circularly polarized luminescence: extension of the excimer chirality rule EN Kazuto Takaishi Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Sho Murakami Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Kazuhiro Iwachido Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University A series of axially chiral binaphthyls and quaternaphthyls possessing two kinds of aromatic fluorophores, such as pyrenyl, perylenyl, and 4-(dimethylamino)phenyl groups, arranged alternately were synthesized by a divergent method. In the excited state, the fluorophores selectively formed a unidirectionally twisted exciplex (excited heterodimer) by a cumulative steric effect and exhibited circularly polarized luminescence (CPL). They are the first examples of a monomolecular exciplex CPL dye. This versatile method for producing exciplex CPL dyes also improved fluorescence intensity, and the CPL properties were not very sensitive to the solvent or to the temperature owing to the conformationally rigid exciplex. This systematic study allowed us to confirm that the excimer chirality rule can be applied to the exciplex dyes: left- and right-handed exciplexes with a twist angle of less than 90 degrees exhibit (-)- and (+)-CPL, respectively. No potential conflict of interest relevant to this article was reported.

Nature Research Acta Medica Okayama 2045-2322 11 1 2021 Enhancement of protein thermostability by three consecutive mutations using loop-walking method and machine learning 11883 EN Kazunori Yoshida Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Shun Kawai Department of Basic Medicinal Sciences, Graduate School of Pharmaceutical Sciences, Nagoya University Masaya Fujitani Department of Basic Medicinal Sciences, Graduate School of Pharmaceutical Sciences, Nagoya University Satoshi Koikeda Innovation Center, Amano Enzyme Inc. Ryuji Kato Department of Basic Medicinal Sciences, Graduate School of Pharmaceutical Sciences, Nagoya University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University We developed a method to improve protein thermostability, "loop-walking method". Three consecutive positions in 12 loops of Burkholderia cepacia lipase were subjected to random mutagenesis to make 12 libraries. Screening allowed us to identify L7 as a hot-spot loop having an impact on thermostability, and the P233G/L234E/V235M mutant was found from 214 variants in the L7 library. Although a more excellent mutant might be discovered by screening all the 8000 P233X/L234X/V235X mutants, it was difficult to assay all of them. We therefore employed machine learning. Using thermostability data of the 214 mutants, a computational discrimination model was constructed to predict thermostability potentials. Among 7786 combinations ranked in silico, 20 promising candidates were selected and assayed. The P233D/L234P/V235S mutant retained 66% activity after heat treatment at 60 degrees C for 30 min, which was higher than those of the wild-type enzyme (5%) and the P233G/L234E/V235M mutant (35%). No potential conflict of interest relevant to this article was reported.

Royal Society of Chemistry Acta Medica Okayama 2041-6520 11 22 2020 Aluminum porphyrins with quaternary ammonium halides as catalysts for copolymerization of cyclohexene oxide and CO2: metal–ligand cooperative catalysis 5669 5675 EN Jingyuan Deng Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo Manussada Ratanasak Institute for Catalysis, Hokkaido University Yuma Sako Graduate School of Natural Science and Technology, Okayama University Hideki Tokuda Graduate School of Natural Science and Technology, Okayama University Chihiro Maeda Graduate School of Natural Science and Technology, Okayama University Jun-ya Hasegawa Institute for Catalysis, Hokkaido University Kyoko Nozaki Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo Tadashi Ema Graduate School of Natural Science and Technology, Okayama University Bifunctional AlIII porphyrins with quaternary ammonium halides, 2-Cl and 2-Br, worked as excellent catalysts for the copolymerization of cyclohexene oxide (CHO) and CO2 at 120 °C. Turnover frequency (TOF) and turnover number (TON) reached 10 000 h−1 and 55 000, respectively, and poly(cyclohexene carbonate) (PCHC) with molecular weight of up to 281 000 was obtained with a catalyst loading of 0.001 mol%. In contrast, bifunctional MgII and ZnII counterparts, 3-Cl and 4-Cl, as well as a binary catalyst system, 1-Cl with bis(triphenylphosphine)iminium chloride (PPNCl), showed poor catalytic performances. Kinetic studies revealed that the reaction rate was first-order in [CHO] and [2-Br] and zero-order in [CO2], and the activation parameters were determined: ΔH‡ = 12.4 kcal mol−1, ΔS‡ = −26.1 cal mol−1 K−1, and ΔG‡ = 21.6 kcal mol−1 at 80 °C. Comparative DFT calculations on two model catalysts, AlIII complex 2′ and MgII complex 3′, allowed us to extract key factors in the catalytic behavior of the bifunctional AlIII catalyst. The high polymerization activity and carbonate-linkage selectivity originate from the cooperative actions of the metal center and the quaternary ammonium cation, both of which facilitate the epoxide-ring opening by the carbonate anion to form the carbonate linkage in the key transition state such as TS3b (ΔH‡ = 13.3 kcal mol−1, ΔS‡ = −3.1 cal mol−1 K−1, and ΔG‡ = 14.4 kcal mol−1 at 80 °C). No potential conflict of interest relevant to this article was reported.

American Chemical Society Acta Medica Okayama 2470-1343 5 17 2020 Minimization of Amounts of Catalyst and Solvent in NHC-Catalyzed Benzoin Reactions of Solid Aldehydes: Mechanistic Consideration of Solid-to-Solid Conversion and Total Synthesis of Isodarparvinol B 10207 10216 EN Kenta Iwai Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Masakazu Ono Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Yoshiko Nanjo Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Tadashi Ema Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University Attempts were made to minimize the amounts of catalyst and solvent in the NHC-catalyzed benzoin reactions of solid aldehydes. In some case, solid-to-solid conversions proceeded in the solvent-free NHC-catalyzed benzoin reactions. Even if a mixture of the substrate, N-heterocyclic carbene (NHC) precursor, and inorganic base was initially a powdery solid, the reaction did proceed at reaction temperature lower than the melting points of each compound. The solid mixture partially melted or became a slurry or suspension in the meantime. We call this solid/liquid mixture a semisolid state. The reaction giving an optically active product was faster than that giving a racemic mixture of the same product. Melting-point depression was observed for a series of mixtures of the substrate and product in different substrate/product ratios. Solvent-free solid-to-solid conversions were accelerated by the formation of a semisolid state resulting from the melting-point depression of the solid substrate accompanied by the product formation. In the case of solid substrates with high melting points, melting-point depression was useless, and the addition of a small amount of solvent was needed. The first total synthesis of isodarparvinol B was achieved via the NHC-catalyzed intramolecular benzoin reaction using a small amount of solvent as an additive. No potential conflict of interest relevant to this article was reported.