Discriminatory drug delivery into target cells is essential to effectively elicit the drug activity and to avoid off-target side effects; however, transporting drugs across the cell membrane is difficult due to factors such as molecular size, hydrophilicity, intercellular adhesiveness, and efflux transporters, particularly, in the brain capillary endothelial cells. Drug delivery into the brain is blocked by the blood–brain barrier (BBB). Thus, developing drugs for the central nervous system (CNS) diseases remains a challenge. The approach based on receptor-mediated transcytosis (RMT) can overcome this impassable problem at the BBB. Well-designed molecules for RMT form conjugates with the ligand and drugs via linkers or nanoparticles. Cell penetrating peptides (CPPs), receptor-targeting peptides, and monoclonal antibodies (mAbs) are often used as ligands. The binding of ligand to the receptor on the endothelial cell surface induces endocytosis. Existing exosomes comprising the conjugates move in the cytoplasm and fuse with the opposite plasma membrane to release them. Subsequently, the transcytosed conjugate-loaded drugs or released drugs from the conjugates elicit activity in the brain. As receptors, transferrin receptor (TfR), low-density lipoprotein receptor (LDLR), and insulin receptor (InsR) have been used to intendedly induce transcytosis. Presently, several clinical trials on CNS drugs for Alzheimer’s and Parkinson disease are hindered due to poor drug distribution into the brain. Therefore, this strategy based on RMT is a promising method for CNS drugs to be transported into the brain. In this review, I introduce the practicality and possibility of drug delivery into brain across the BBB using RMT.

Herein, we describe a novel synthetic method for 2,5-disubstituted tetrazoles from 5-substituted tetrazoles using cobalt-catalyzed intermolecular hydroamination reaction of nonactivated olefins. Owing to its mild conditions, the method enabled the use of substrates having acid-labile functional groups, such as silyloxy and methoxymethyloxy groups. By using optically active cobalt complexes, asymmetric intermolecular hydroamination of nonactivated olefins, a longstanding challenge in synthetic organic chemistry, was developed to produce optically active disubstituted tetrazoles.

Respiratory syncytial virus (RSV) is one of the most common causes of lower respiratory tract infections and a significant pathogen for both adults and children. Although two drugs have been approved for the treatment of RSV infections, the low therapeutic index of these drugs have led pharmaceutical companies to develop safe and effective small-molecule anti-RSV drugs. The pyrazolo[1,5-a]pyrimidine series of compounds containing a piperidine ring at the 2-position of the pyrazolo[1,5-a]pyrimidine scaffold are known as candidate RSV fusion (F) protein inhibitor drugs, such as presatovir and P3. The piperidine ring has been revealed to facilitate the formation of an appropriate dihedral angle between the pyrazolo[1,5-a]pyrimidine scaffold and the plane of the amide bond for exertion of anti-RSV activity. A molecular-dynamic study on newly designed compounds with an acyclic chain instead of the piperidine ring proposed and demonstrated a new series of pyrazolo[1,5-a]pyrimidine derivatives, such as 9c with a 1-methyaminopropyl moiety, showing similar dihedral angle distributions to those in presatovir. Compound 9c exhibited potent anti-RSV activity with an EC₅₀ value of below 1 nM, which was similar to that of presatovir. A subsequent optimization study on the benzene ring of 9c led to the potent RSV F protein inhibitor 14f with an EC₅₀ value of 0.15 nM. The possibility of improving the biological properties of anti-RSV agents by modification at the 7-position of pyrazolo[1,5-a]pyrimidine is also discussed.

The cryptolactones A₁, A_2, B₁, and B₂ isolated from a Cryptomyzus sp. aphid were synthesized via the Mukaiyama aldol reaction and olefin metathesis. Their antipodes and derivatives were also synthesized by the same strategy to investigate structure–activity relationships. These compounds exhibited cytotoxic activity against human promyelocytic leukemia HL-60 cells with IC₅₀ values of 2.1–42 µM.

Various aromatic lactones have been synthesized and their regioselectivity (1,2-addition vs. 1,4- or 1,6-addition) investigated in reactions with organolithium species, particularly n-BuLi and sec-BuLi. The regioselectivity varied greatly depending on various factors, such as the bulkiness of both substrates and organolithium species, and types of solvent and cosolvent. In particular, 1,4-addition with dearomatization occurred preferentially using sec-BuLi as the nucleophile in tetrahydrofuran (THF) with hexamethylphosphoramide (HMPA) or N,N′-dimethylpropyleneurea (DMPU) as cosolvent. For sec-BuLi, the reaction was estimated to proceed through a single-electron transfer mechanism.

Oxo-octadecadienoic acids (OxoODEs) act as peroxisome proliferator-activated receptor (PPAR) agonists biologically, and are known to be produced in the lipoxygenase/linoleate system. OxoODEs seem to originate from the linoleate alkoxyl radicals that are generated from (E/Z)-hydroperoxy octadecadienoic acids ((E/Z)-HpODEs) by a pseudoperoxidase reaction that is catalyzed by ferrous lipoxygenase. However, the mechanism underlying the conversion of alkoxyl radical into OxoODE remains obscure. In the present study, we confirmed that OxoODEs are produced in the lipoxygenase/linoleate system in an oxygen-dependent manner. Interestingly, we revealed a correlation between the (E/Z)-OxoODEs content and the (E/E)-HpODEs content in the system. (E/E)-HpODEs could have been derived from (E/E)-linoleate peroxyl radicals, which are generated by the reaction between a free linoleate allyl radical and an oxygen molecule. Notably, the ferrous lipoxygenase-linoleate allyl radical (LOx(Fe²⁺)-L·) complex, which is an intermediate in the lipoxygenase/linoleate system, tends to dissociate into LOx(Fe²⁺) and a linoleate allyl radical. Subsequently, LOx(Fe²⁺) converts (E/Z)-HpODEs to an (E/Z)-linoleate alkoxyl radical through one-electron reduction. Taken together, we propose that (E/Z)-OxoODEs and (E/E)-HpODEs are produced through radical–radical dismutation between (E/Z)-linoleate alkoxyl radical and (E/E)-linoleate peroxyl radical. Furthermore, the production of (E/Z)-OxoODEs and (E/E)-HpODEs was remarkably inhibited by a hydrophobic radical scavenger, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). On the contrary, water-miscible radical scavengers, 4-hydroxyl-2,2,6,6-tetramethylpiperidine 1-oxyl (OH-TEMPO) and 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrroline-N-oxyl (CmΔP) only modestly or sparingly inhibited the production of (E/Z)-OxoODEs and (E/E)-HpODEs. These facts indicate that the radical–radical dismutation between linoleate alkoxyl radical and linoleate peroxyl radical proceeds in the interior of micelles.

In optogenetics, red-shifted channelrhodopsins (ChRs) are eagerly sought. We prepared six kinds of new chromophores with one double bond inserted into the polyene side chain of retinal (A1) or 3,4-didehydroretinal (A2), and examined their binding efficiency with opsins (ReaChR and ChrimsonR). All analogs bound with opsins to afford new ChRs. Among them, A2-10ex (an extra double bond is inserted at the C10–C11 position of A2) showed the greatest red-shift in the absorption spectrum of ChrimsonR, with a maximum absorbance at 654 nm (67 nm red-shifted from that of A1-ChrimsonR). Moreover, a long-wavelength spectral boundary of A2-10ex-ChrimsonR was extended to 756 nm, which reached into the far-red region (710–850 nm).

Phytochemical analysis of the whole Helleborus foetidus plants identified 28 steroidal glycosides (1–28), including 20 novel spirostanol glycosides (1–20) and a novel furostanol glycoside (21). The structures of the newly identified compounds were elucidated by two-dimensional NMR spectroscopy and hydrolytic cleavage. Compounds 12, 13, and 15 were determined to be spirostanol trisdesmosides bearing sugar moieties at the C-1, -21, and -24 hydroxy groups of the aglycone unit. The isolated compounds were subsequently evaluated for cytotoxic activity against HL-60 human promyelocytic leukemia cells and A549 human lung carcinoma cells. In particular, 7 showed cytotoxic activity against the HL-60 and A549 cells, with IC₅₀ values of 5.9 and 6.6 µM, respectively, whereas 19 was selectively cytotoxic to A549 cells with an IC₅₀ value of 5.5 µM.

The merits of biogenetic considerations in the chemical syntheses of natural products have been emphasized by describing the total syntheses of Lycopodium alkaloids; lycodine, flabellidine, lycopodine, and flabelliformine, as well as monoterpenoid indole alkaloids; C-mavacurine, kopsiyunnanine K, koumine, and 11-methoxy-19R-hydroxygelselegine.

The total syntheses of dimeric indole alkaloids, haplophytine, and T988s are described. These dimeric compounds comprising two structurally different indole units are ubiquitous in nature, and many possess pharmaceutically important activities. To realize an efficient chemical synthesis of these dimeric indole alkaloids, the establishment of convergent synthetic strategies and development of new coupling methods are indispensable. The linkage of two highly functionalized units at a late stage of the synthesis frequently induces synthetic problems such as chemoselectivity and steric repulsion. Moreover, although transition metal-catalyzed reactions are usually an effective method for the cross-coupling of two units, the application of these cross-coupling reactions to bond formation involving a sterically hindered C(sp³) is often difficult. Thus, even with precise modern synthetic methods, it is currently difficult to realize convergent syntheses of dimeric indole alkaloids possessing a quaternary carbon linking two units. To combat these synthetic problems, we developed a synthetic method to link two indole units using an Ag-mediated nucleophilic substitution reaction. In this review, we provide a detailed discussion of convergent synthetic strategies and coupling methods for dimeric indole alkaloids.

Efficient methods for delivery of antisense DNA or small interfering RNA (siRNA) are highly needed. Cationic materials, which are conventionally used for anionic oligonucleotide delivery, have several drawbacks, including aggregate formation, cytotoxicity and a low endosome escape efficiency. In this report a bio-reactive mask (i.e., disulfide unit) for cationic amino groups was introduced, and the mask was designed such that it was removed at the target cell surface. Insolubility and severe cellular toxicity caused by exposed cationic groups are avoided when using the mask. Moreover, the disulfide unit used to mask the cationic group enabled direct delivery of oligonucleotides to the cell cytosol. The molecular design reported is a promising approach for therapeutic applications.

Previously, we reported that the c-Met inhibitory effect of Ephedra Herb extract (EHE) is derived from ingredients besides ephedrine alkaloids. Moreover, analgesic and anti-influenza activities of EHE and ephedrine alkaloids-free Ephedra Herb extract (EFE) have been reported recently. In this study, we examined the fractions containing c-Met kinase inhibitory activity from EHE and the fractions with analgesic and anti-influenza activities from EFE, and elucidated the structural characteristics of the active fractions. Significant c-Met kinase activity was observed in 30, 40, and 50% methanol (MeOH) eluate fractions obtained from water extract of EHE using Diaion HP-20 column chromatography. Similarly, 20 and 40% MeOH, and MeOH eluate fractions obtained from water extract of EFE were found to display analgesic and anti-influenza activities. Reversed phase-HPLC analysis of the active fractions commonly showed broad peaks characteristic of high-molecular mass condensed tannin. The active fractions were analyzed using ¹³C-NMR and decomposition reactions; the deduced structures of active components were high-molecular mass condensed tannins, which were mainly procyanidin B-type and partly procyanidin A-type, including pyrogallol- and catechol-type flavan 3-ols as extension and terminal units. HPLC and gel permeation chromatography (GPC) analyses estimated that the ratio of pyrogallol- and catechol-type was approximately 9 : 2, and the weight-average molecular weight based on the polystyrene standard was >45000. Furthermore, GPC-based analysis was proposed as the quality evaluation method for high-molecular mass condensed tannin in EHE and EFE.

Novel reactions using hetero-heavy atoms (P, S, Si, Se, and Sn) were developed and applied to the synthesis of biofunctional molecules and some medicine-candidates, in which the following items are covered. 1) Development of introduction of C₁-unit using cyanophosphates (CPs). 2) Carbene-generation under neutral condition from CPs and its application to organic synthesis. 3) [3,3]Sigmatropic rearrangement-ring expansion reactions of medium-sized cyclic thionocarbonates containing a sulfur atom and their application to natural product synthesis. 4) Stereoselective synthesis of novel β-imidazole C-nucleosides via diazafulvene intermediates and their application to investigating ribozyme reaction mechanism. 5) Developments of novel histamine H₃- and H₄-receptor ligands using new synthetic methods involving Se or Sn atoms.

Enzymatic and post-translational modifications (PTMs) such as ubiquitination, acetylation, and methylation occur at lysine residues. The PTMs play critical roles in the regulation of the protein functions, and thus, various cellular processes. In addition, aberrations of the PTMs are associated with various diseases, such as cancer and neurodegenerative disorders. Therefore, we hypothesized that modulation of the PTMs and normalization of the PTM abnormalities could be useful as methods to control various cellular mechanisms and as a therapeutic strategy, respectively. To modulate the PTMs, we have focused on lysine-modifying enzymes and have pursued drug discovery researches on ubiquitination inducers, lysine deacetylase (KDAC) inhibitors, and lysine demethylase (KDM) inhibitors. For the identification of the modulators, we have used not only conventional drug design, such as structure-based drug design (SBDD) and ligand-based drug design (LBDD), but also “strategic chemistry approaches,” such as drug design based on enzyme catalytic mechanism. As a result, we have identified several modulators which have pharmacological effects in animal models or in cellular studies. In this review, focusing on the drug design based on enzyme catalytic mechanism, our drug discovery researches have been discussed.

Novel 3,5-dimethylpyridin-4(1H)-one scaffold compounds were synthesized and evaluated as AMP-activated protein kinase (AMPK) activators. Unlike direct AMPK activators, this series of compounds showed selective cell growth inhibitory activity against human breast cancer cell lines. By optimizing the lead compound (4a) from our library, 2-[({1′-[(4-fluorophenyl)methyl]-2-methyl-1′,2′,3′,6′-tetrahydro[3,4′-bipyridin]-6-yl}oxy)methyl]-3,5-dimethylpyridin-4(1H)-one (25) was found to have potent AMPK activating activity. Compound 25 also showed good aqueous solubility while maintaining the unique selectivity in cell growth inhibitory activity.

Euglena gracilis EOD-1, a microalgal strain, produces large quantities of paramylon, a class of polymers known as β-1,3-glucans and has been reported to function as a dietary fiber and to improve the metabolic syndrome including obesity. However, despite its importance, the morphometric analysis of paramylon has not been conducted so far. In this study, we attempted to observe the detailed three-dimensional structure of paramylon by focused ion beam/scanning electron microscopy (FIB/SEM). Paramylon samples were fixed and three-dimensional image reconstruction and segmentation of the image stack were created using computer software (Amira v6.0.1, FEI). The results indicated that the inside of paramylon particles (diameter: 5 µm, thickness: 3 µm) was comprised of a dense structure with no evidence of the presence of large pores and gaps, although a small 100 nm crack was observed. The specific surface area of paramylon particles measured by the Brunauer–Emmet–Teller (BET) method, was not as large as activated charcoal, but similar to those of plant starches, indicating that the cholesterol-lowering effect of paramylon cannot be simply attributed to its adsorption ability. The FIB/SEM method was found to be useful for elucidating the internal structure of small solid particles.

The biary unit having heteroatom as important scaffolds widely exist in a large number of biologically active compounds and functional organic molecules. Since the cross-coupling is a useful synthetic method for constructing biaryl and heterobiaryl structures, the development of novel cross-coupling methods has been studied intensively. The oxidative biaryl coupling reaction of aromatic compounds having heteroatoms is an attractive method since they do not require the prefunctionalization of arenes. This report describes recent advances in hypervalent iodine(III) induced metal-free synthesis of biaryls having heteroatoms.

A pharmacopoeia’s core mission is to protect public health by creating and making available public standards to help ensure the quality of drugs. In recent years, pharmacopoeias around the world have harmonized their standards in the present context of globalized drug supply chains and markets. For example, the Pharmacopoeial Discussion Group has worked to harmonize excipient monographs and general chapters. In addition, the International Meeting of World Pharmacopoeias has been held by the WHO to discuss information exchange and international collaboration, among other topics. To contribute further to the protection of public health in the globalized drug market, we conducted a comparative study of the pharmacopoeias in Japan, Europe, and the United States. We aimed to examine current differences among the Japanese Pharmacopoeia, the European Pharmacopoeia, and the United States Pharmacopeia–National Formulary and to identify areas that require further collaboration among the three pharmacopoeias. In this study, we analyzed monographs and general chapters listed in the three pharmacopoeias. We identified the features of the monographs and general chapters listed in each pharmacopoeia, as well as differences across the pharmacopoeias. Moreover, on the basis of our findings, we suggest standards that require further collaboration among the pharmacopoeias in certain preferred areas. The comparison data produced by this study are expected to be used to develop strategies for future revisions of pharmacopoeias around the world.

The 1-BuOH-soluble fraction of the methanol (MeOH) extract of Diospyros maritima was separated by chromatographic techniques to give three new oleanane-type and one new ursane-type triterpene glucoside, named ebenamariosides A–D (1–4); two megastigmanes were also isolated. The structures of triterpene glucosides was elucidated with extensive investigation by one and two dimensional NMR spectroscopy and the structures were confirmed by partial enzymatic hydrolyses to give the corresponding mono-glucosides and aglycones. The structures of the megastigmanes, including their absolute stereochemistries, were elucidated by spectroscopic evidence and by the modified Mosher’s method. Two megastigmanes were chemically correlated and their absolute structures were unambiguously determined. The cytotoxicity of the triterpene glucosides and their degradation products were assayed. They did not show any significant activity.