The ability to control the reactions of highly active chemical species to enable straightforward synthesis of valuable compounds such as bioactive natural products and pharmaceuticals is a continuing challenge in synthetic organic chemistry. This review describes the development of a methodology using reactive metal-carbene species and its synthetic application in our laboratory. First, regioselective synthesis of γ-amino acid equivalents to take advantage of their metal-dependent reactivities and the mechanistic rationale are presented. Chemoselective and enantioselective dearomatization reactions of several arenes with silver-carbene are also discussed. In the second half of the review, we discuss a carbene-insertion reaction into an amide and urea C–N bond for the assembly of nitrogen-bridged cyclic molecules.

A series of quinone derivatives with a variety of side chains were synthesized. These synthetic quinone compounds were evaluated for in vitro antitrypanosomal activity against trypomastigotes and amastigotes of Trypanosoma cruzi, the causative agent of Chagas disease. Measurement of solubility of quinones and their ability to permeate cell membranes were assessed to address their possible use as oral drugs. Some synthesized compounds exhibited potent antitrypanosomal activity. However, most compounds with a promising activity showed poor solubility that did not seem suitable for oral usage. Meanwhile, compound 5a, an N-tert-butoxycarbonylpiperidine derivative, exhibited good antitrypanosomal activity, ability to permeate membranes, and good solubility.

Extracellular vesicles (EVs) have emerged as important targets in biological and medical studies because they are involved in diverse human diseases and bacterial pathogenesis. Although antibodies targeting the surface biomarkers are widely used to detect EVs, peptide-based curvature sensors are currently attracting an attention as a novel tool for marker-free EV detection techniques. We have previously created a curvature-sensing peptide, FAAV and applied it to develop a simple and rapid method for detection of bacterial EVs in cultured media. The method utilized the fluorescence/Förster resonance energy transfer (FRET) phenomenon to achieve the high sensitivity to changes in the EV amount. In the present study, to develop a practical and easy-to-use approach that can detect bacterial EVs by peptides alone, we designed novel curvature-sensing peptides, N-terminus-substituted FAAV (nFAAV) peptides. The nFAAV peptides exerted higher α-helix-stabilizing effects than FAAV upon binding to vesicles while maintaining a random coil structure in aqueous solution. One of the nFAAV peptides showed a superior binding affinity for bacterial EVs and detected changes in the EV amount with 5-fold higher sensitivity than FAAV even in the presence of the EV-secretory bacterial cells. We named nFAAV5, which exhibited the high ability to detect bacterial EVs, as an EV-sensing peptide. Our finding is that the coil–α-helix structural transition of the nFAAV peptides serve as a key structural factor for highly sensitive detection of bacterial EVs.

From the viewpoint of self-medication, it is valuable to develop patient-friendly scored tablets that possess dividing uniformity. In this context, we attempted to optimize the preparation conditions for a tablet with a unique shape, such as a concavely curved scored tablet (CCST). Employing a design of experiment and a response surface method incorporating a thin-plate spline interpolation, and a bootstrap resampling technique, the optimal preparation conditions for CCST were successfully developed. To make it possible to scaleup the optimal solution estimated on a trial-scale, a Bayesian estimation was applied. Credible ranges of critical responses in large-scale manufacturing were estimated as a posterior probability from the trial-scale experiment as a prior probability. In terms of the large-scale manufacturing, the possibility of solving the scaleup problem was suggested using Bayesian estimation. Furthermore, a simulation study using a finite element method revealed that strong tensile stresses generated along the tip of the score line in CCST when an outer force was applied to the back surface of CCST. An advantage in dividing uniformity is indicated by the unique shape of CCST.

In this study, a series of alkyl diamine linked bivalent β-carbolines was synthesized and evaluated as antitumor agent. The results demonstrated that most compounds displayed good antiproliferative activities with IC₅₀ value lower than 10 µM against a panel of human tumor cell lines, and compound 8 was found to be the most potent antiproliferative agent with IC₅₀ value of 1.39, 1.96, 1.42, 1.49, 1.32, 1.96 and 1.63 µM against human breast cancer cell line (MCF-7), human adenocarcinoma cell line (769-P), human malighant melanoma cell line (A375), human ovarian cancer cell line (SK-OV-3), human colon carcinoma cell line (HCT-116), human gastric cancer cell line (BGC-823) and human esophageal squamous carcinoma cell line (Eca-109), respectively. Further investigations on mechanism of action of this class of compound demonstrated that the representative compound 8 inhibited colorectal cancer growth through inducing autophagy.

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step of the nicotinamide adenine dinucleotide (NAD⁺) salvage pathway. Because NAD⁺ plays a pivotal role in energy metabolism and boosting NAD⁺ has positive effects on metabolic regulation, activation of NAMPT is an attractive therapeutic approach for the treatment of various diseases, including type 2 diabetes and obesity. Herein we report the discovery of 1-(2-phenyl-1,3-benzoxazol-6-yl)-3-(pyridin-4-ylmethyl)urea 12c (DS68702229), which was identified as a potent NAMPT activator. Compound 12c activated NAMPT, increased cellular NAD⁺ levels, and exhibited an excellent pharmacokinetic profile in mice after oral administration. Oral administration of compound 12c to high-fat diet-induced obese mice decreased body weight. These observations indicate that compound 12c is a promising anti-obesity drug candidate.

Control of site selectivity is an exciting direction for synthetic organic chemistry owing to the possibility of selective modification of multifunctionalized molecules, ultimately including biomacromolecules. In this review, our recent research related to site selectivity in two types of transformation, namely, the acylation of hydroxy groups and C–H amination, is summarized. Regarding the acylation of hydroxy groups, catalyst-controlled site selectivity enables unconventional retrosynthetic analysis, leading to efficient syntheses of sugar-related natural and unnatural products. Regarding C–H amination, the discovery of unprecedented reaction sites in intermolecular amination mediated by dirhodium nitrenes is described. The findings of this research demonstrate the power of site-selective transformation in the synthesis of a particular class of compounds.

Nitroxyl radicals, such as 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), can catalyze the electrochemical oxidation of alcohols and amines. Because the oxidation current obtained in this process depends on the concentration of alcohols and amines, this process can be applied to their sensing. However, the relatively high oxidation potentials required by nitroxyl radicals can induce interfering oxidation currents from various reductive substances in biological samples, which affects the accuracy of analyte measurements. In this study, we examined the electrooxidation of alcohols and amines at a low potential by applying cooperative oxidation catalysis using a nitroxyl radical and a copper salt. Nortropine N-oxyl (NNO), which showed higher catalytic activity than TEMPO was used as the nitroxyl radical. An increase in the oxidation current was observed at the low potential, and this increase depended on the alcohol concentration. In the case of the electrooxidation of amines, a positive correlation between oxidation current and amine concentration was observed at low amine concentrations. Therefore, low-potential cooperative catalysis can be applied to alcohol and amine electrooxidation for the development of accurate sensors suitable for clinical settings.

α,β-Unsaturated oximes underwent electrophilic epoxidation with in-situ-generated dimethyldioxirane to give the corresponding epoxides in good yields. This reaction is an example of “carbonyl umpolung” by transformation of α,β-unsaturated ketones to their oximes. Nucleophilic ring-opening reactions of the epoxides afforded α-substituted products. Shi asymmetric epoxidation of the oximes proceeded with moderate enantioselectivity.

Spiroviolene is a spirocyclic triquinane diterpene produced by Streptomyces violens. Recently, a biosynthetic pathway that includes secondary carbocation intermediates and a complicated concerted skeletal rearrangement was proposed for spiroviolene, based upon careful labeling experiments. On the basis of density functional theory (DFT) calculations, we propose a revised pathway for spiroviolene biosynthesis, involving a multistep carbocation cascade that bypasses the formation of unstable secondary carbocations by breaking the adjacent C–C bond to form a more stable tertiary carbocation (IM3) and by Wagner–Meerwein 1,2-methyl rearrangement (IM7).

Novel innovative catalytic systems such as hydrogen-bond donors and thiourea hybrid catalysts have been developed for the asymmetric synthesis of biologically important pharmaceuticals and natural products. Benzothiadiazines possess a stronger hydrogen-bond donor ability compared to thioureas and exhibit remarkable catalytic performance for the activation of α,β-unsaturated amides. Hybrid thioureas (bearing an arylboronic acid and an ammonium salt) efficiently promote the hetero-Michael addition to α,β-unsaturated carboxylic acids and the O-alkylation of keto enols with 5-chlorofuran-2(5H)-one. These hybrid catalysts enable the first total synthesis of non-racemic avenaol, a noncanonical strigolactone, as well as the asymmetric synthesis of several pharmaceuticals. In addition, this study discovers unique chemical phenomena (i.e., the dual role of benzoic acid as a boron ligand and a proton shuttle, the chirality switch of products by solvent used, and the dynamic kinetic resolution of a racemic electrophile in an S_N2-type reaction).

Active pharmaceutical ingredients (APIs) have become a public concern owing to their possible adverse effects on aquatic organisms. Ministry of Health, Labor and Welfare in Japan (MHLW) issued “Guidance on the Environmental Risk Assessment (ERA) in new pharmaceutical development” in 2016. To evaluate the validity of phase 1 in the MHLW’s ERA guidance, we monitored the measured environmental concentrations (MECs) of approved APIs in urban rivers and sewage treatment plants (STPs) in Japan and compared these MECs with the predicted environmental concentration (PEC). We collected water samples from urban seven rivers and three STPs during each season. Fifty-one APIs for human and veterinary use and the artificial sweetener sucralose were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Forty-four APIs were observed in the rivers and 42 were found in the influent and effluent of STPs, with levels ranging from nanograms to micrograms per liter. The action limit in phase I of the MHLW’s guidance was set to 10 ng/L, and there was no API except for ketoprofen, for which PEC of the MHLW’s guidance (PECjapan) was lower than 10 ng/L and the maximum MEC (MECmax) was 10 ng/L or greater. Almost all APIs also had median MECs that were lower than those of the respective PECjapan. These results indicate that the PECjapan values in phase I of the MHLW’s guidance were appropriate. However, some APIs had MECmax values that were greater than those of the respective PECjapan due to overestimation of the dilution factor of river water and/or underestimation of API production.

Proviral integration site for Moloney murine leukemia virus (PIM) kinases are proto-oncogenic kinases involved in the regulation of several cellular processes. PIM kinases are promising targets for new drug development because they play a major role in many cancer-specific pathways, such as survival, apoptosis, proliferation, cell cycle regulation, and migration. Here, 2-thioxothiazolidin-4-one derivatives were synthesized and evaluated as potent pan-PIM kinase inhibitors. Optimized compounds showed single-digit nanomolar IC₅₀ values against all three PIM kinases with high selectivity over 14 other kinases. Compound 17 inhibited the growth of Molm-16 cell lines (EC₅₀ = 14 nM) and modulated the expression of pBAD and p4EBP1 in a dose-dependent manner.

The aim of this study was to evaluate the effect of three coformers and five disintegrants in the granulation formulation on the dissociation of cocrystal during the granulation process by monitoring wet granulation with probe-type low-frequency Raman (LF-Raman) spectroscopy. As model cocrystals, paracetamol (APAP)-oxalic acid (OXA), APAP-maleic acid (MLA), and APAP-trimethylglycine (TMG) were used. The monitoring of the granulation recipe containing cocrystals during wet granulation was performed over time with high-performance LF-Raman spectrometry and the dissociation rate was calculated from the results of multivariate analysis of LF-Raman spectra. The dissociation rate decreased in the order of APAP-TMG, APAP-OXA, and APAP-MLA, showing the same order as observed in Powder X-ray diffraction measurements. Furthermore, to compare the effect of disintegrants on the dissociation rate of APAP-OXA, LF-Raman monitoring was performed for the granulation recipes containing five typical disintegrants (two low-substitution hydroxypropyl cellulose (HPC), cornstarch (CSW), carmellose sodium (CMC), and crospovidone (CRP)). The dissociation rate of APAP-OXA decreased in the order of CSW, HPCs, CMC, and CRP. This difference in the dissociation rate of APAP-OXA was thought to be due to the disintegration mechanism of the disintegrants and the water absorption ratio, which was expected to affect the water behavior on the disintegrant surface during wet granulation. These results suggested that probe-type LF-Raman spectroscopy is useful to monitor the dissociation behavior of cocrystals during wet granulation and can compare the relative stability of cocrystal during wet granulation between different formulations.

Acyclic asymmetric quaternary stereocenters, which are composed of four carbon-carbon bonds, were finely constructed by utilizing a face-selective alkylation of enolate intermediates derived from an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. The present face-selective alkylation was able to employ diverse alkyl halides as an electrophile to afford various Michael adducts having an all-carbon quaternary stereocenter. With regard to the deprotection of the chiral auxiliary, N-iodosuccinimide used in our previous study did not work in the present cases; however, we found that pyridine iodine monochloride in the presence of H₂O was effective to remove the bornyl group and the benzyl group on the amino group to provide the β-amino ester derivative.

This account summarizes the development of a benzyne-mediated cyclization/functionalization protocol for the versatile construction of highly substituted benzene derivatives fused with an N-heterocyclic ring such as indolines, indoles, and related nitrogen-containing heterocycles. The protocol comprises sequential reactions initiated by generating a benzyne species and subsequent cyclization via addition of magnesium amide to the benzyne, followed by trapping of the resultant magnesium compound in situ with various electrophiles. The substituent scope was expanded by conducting a transmetalation on a copper species to introduce alkyl, aryl, and alkenyl substituents. The utility of the sequential reaction was demonstrated in the synthesis of a carbazole natural product (heptaphylline), pyrrolo[4,3,2-de]quinoline alkaloids (batzellines), and pyrrolo[2,3-c]carbazole alkaloids (dictyodendrines).

Hospital preparations are frequently prepared in Japanese hospitals when ready-made formulations to meet patients’ needs are unavailable. Although the quality of hospital preparations have to be ensured for efficacy and safety, such quality evaluation tends to be insufficient mainly due to lack of manpower and experimental environments in hospitals. In this paper, we investigated the applicability of quantitative (q)NMR spectroscopy to the quality control of diclofenac gargles as examples of hospital preparations, as it has various merits for the quantitative analysis of mixtures in solutions. Diclofenac gargles are composed of diclofenac, tranexamic acid, and lidocaine, and are used for the pain relief of stomatitis induced by cancer chemotherapy. Aliquots of the gargles, which were prepared five times, were mixed with dimethylsulfone as an internal standard, followed by qNMR measurements. Water signal suppression was achieved using a pulse program, water suppression enhanced through T₁ effects, because the pulse program was superior to other ones such as presaturation and one-dimensional nuclear Overhauser effect spectroscopy in terms of quantitativeness. Concentrations of the three medicinal ingredients were simultaneously determined based on the signals selected by considering the spectral separation and the quantitativeness. Consequently, the gargles were found to be prepared with constant quality, and were stable at room temperature for at least four weeks. qNMR is considered to be potentially useful for the quality control of various hospital preparations because of minimal sample pretreatments, lack of need of calibration curves, and its comprehensive detection abilities.

The particles of phenytoin (Phe), a poorly water-soluble model drug, were bead-milled alone or co-milled with a hydrophilic waxy additive using an ultra cryo-milling technique in liquid nitrogen (LN₂) to improve its dissolution properties. However, the micronized drug particles adhered and aggregated, resulting in poor handling in manufacturing processes such as blending or tableting. To improve the dissolution profile and powder properties of the drug simultaneously, the milled products were secondarily processed together with larger spherical particles by mechanical powder processing. These secondary products were composite particles with a core-shell structure, with fine drug particles adhered and deposited on the core, based on order mixing theory. As a core, three types/sizes of spherical pharmaceutical excipient particles were applied. The resultant composite particles produced much faster release profiles than just milled or co-milled mixtures. In addition, the composite particles showed good micromeritic properties depending on the size of the core particles. These results indicate that the ultra cryo-milling and subsequent dry composite mixing is a potential approach for developing drug particles with improved dissolution.

The irradiation of halogen-bonded complexes with light leads to the homolysis of carbon–halogen bonds and the formation of the corresponding carbon radical species. However, the only methodology reported for these halogen-bonding complexes is using CBr₄ as the halogen-bond donor and its applicability is of great interest. In this study, the atom transfer radical addition (ATRA) reaction of olefins using bromomalonates as halogen-bonding donors was developed. Using 4-phenylpyridine as the halogen-bonding acceptor, the desired reaction proceeded well under external irradiation of 380 nm light to furnish the corresponding ATRA reaction product. The ATRA reaction was effective in generating the corresponding products for a variety of olefins. Furthermore, the ATRA reaction was applicable to bulky ketones, substrates, and malonate esters. The intermediates of the reaction were identified and a plausible reaction mechanism was proposed.