To develop potent ligands for the vitamin D receptor (VDR), we designed and synthesized a series of vitamin D analogues with and without 22-alkyl substituents. These analogues exhibited agonistic, partial agonistic, or antagonistic activity. To elucidate the mechanism of action of the analogues, we conducted crystal structure analyses of the ligand-binding domain (LBD) of VDR complexed with the analogues. The VDR-LBD/agonist complex exhibited precise interactions, which clearly explained VDR agonism. The VDR-LBD/partial agonist complex showed two conformers (agonist and antagonist binding conformers) in a single crystal, demonstrating that partial agonism could be explained by the sum of the agonistic and antagonistic activities. Antagonist binding to the VDR-LBD structure was elucidated using both crystal structure analysis and in-solution structural analyses with the small-angle X-ray scattering (SAXS)-molecular dynamics (MD) and hydrogen/deuterium exchange coupled with mass spectrometry (HDX-MS) methods. Several antagonist-binding structures were detected. We found that the antagonist binding structures differed depending on the structure of the antagonist itself, and those structures clearly explained the VDR antagonism. Furthermore, the apo VDR-LBD structure without the ligand in the ligand-binding pocket was revealed and found to have an entrance to accommodate the ligand. Thus we elucidated the mechanisms of action of agonists, partial agonists, and antagonists based on structural changes (differences) in the receptor protein induced by ligand binding.

Natural products are still rich sources of clinically used medicines and lead compounds for them. This review summarizes chemical studies carried out by the author on natural products of microorganism origin, many of which were discovered at the Institute of Microbial Chemistry (BIKAKEN). Caprazamycin B is a liponucleoside antibiotic from which CPZEN-45, an antituberculosis agent with a unique mode of action, was developed. Intervenolin and leucinostatin A exert antiproliferative activity toward tumor cells in the presence of the corresponding stromal cells, which implies that the primary molecular targets of these molecules should be related to growth signals from normal (stromal) cells. Details of the endeavors to establish efficient synthetic routes to these compounds which accelerated structure–activity relationship studies and further evaluation of biological activity are described.

The mango tree (Mangifera indica L.) is a tropical, perennial, woody evergreen plant belonging to the Anacardiaceae. In traditional medicine, dried mango tree leaves were considered useful in treating diabetes and respiratory infections. In this paper, we review the phytochemical research on mango leaves and the mechanisms of benzophenones in lipid metabolism regulation. Thirty-six benzophenones have been isolated from mango leaves; among them, mangiferin is the major compound. Structure–activity relationships of benzophenones in lipid accumulation and the mechanisms of action of mangiferin in lipid metabolism are summarized. After oral administration, mangiferin is partly converted to its active metabolite, northyariol, which contributes to the activation of sirtuin-1 and liver kinase B1 and increases the intracellular AMP level and AMP/adenosine triphosphate ratio, followed by AMP-activated protein kinase phosphorylation, leading to increased phosphorylation of sterol regulatory element-binding protein-1c. Current evidence supports ethnopharmacological uses of mango leaves in diabetes and points toward potential future applications.

Neuroinflammation manifested by over-activation of microglial cells plays an essential role in neurodegenerative diseases. Short-term activation of microglia can be beneficial, but chronically activated microglia can aggravate neuronal dysfunction possibly by secreting potentially cytotoxic substances such as tumor necrosis factor-alpha (TNF-α) and nitric oxide (NO), which can result in dysfunction and death of neurons. Therefore inhibiting over-activation of microglia and the production of cytotoxic intermediates may become an effective therapeutic approach for neuroinflammation. In this paper, we review our continuous research on natural inhibitors of over-activated microglia from traditional herbals, including flavonoids, lignans, sesquiterpene coumarins, and stilbenes.

Diabetic embryopathy is a diabetic complication, in which maternal hyperglycemia in early pregnancy causes birth defects in newborn infants. Under maternal diabetic conditions, hyperglycemia disturbs intracellular molecular activities and organelles functions. These include protein misfolding in the endoplasmic reticulum (ER), overproduction of reactive oxygen species (ROS) in mitochondria, and high levels of nitric oxide (NO). The resultant ER, oxidative, and nitrosative stresses activate apoptotic machinery to cause cell death in the embryo, ultimately resulting in developmental malformations. Based on the basic research data, efforts have been made to develop interventional strategies to alleviate the stress conditions and to reduce embryonic malformations. One of the challenges in birth defect prevention is to identify effective and safe agents to be used in pregnancy. One approach is to search and characterize naturally occurring phytochemicals, including flavonoids, curcuminoids and stilbenoids, for use in prevention of diabetic embryopathy.

Quassinoids, one kind of triterpenoids with multiple bioactivities such as anti-cancer, anti-malarial, anti-oxidative, anti-microbial, anti-diabetic, anti-viral, and anti-inflammatory effects, have drawn much attention in recent years. Between 2004 and 2018, the structural characteristics and plant sources of 190 quassinoids were reported. Herein, the structure–activity relationships (SARs) of quassinoids along with the anti-cancer mechanisms of four representative quassinoids, eurycomanone, bruceine D, dehydrobruceine B, and brusatol are discussed. This review might be useful for further research and development of quassinoids.

Dimeric sesquiterpene thioalkaloids from the rhizomes of Nuphar pumilum exhibited immunosuppressive effects using a sheep erythrocyte plaque forming cell (PFC) assay, as well as an anti-metastasis effect, and rapid apoptosis-inducing effects in tumor cell lines. In particular, dimeric sesquiterpene thioalkaloids with a hydroxy group (6-hydroxythiobinupharidine, 6,6′-dihydroxythiobinupharidine, 6-hydroxythionuphlutine B) showed substantial effects, whereas dimeric sesquiterpene thioalkaloids lacking the hydroxy group (thiobinupharidine, thionuphlutine B, 6′-hydroxythionuphlutine B, neothiobinupharidine, thionuphlutine B β-sulfoxide, neothiobinupharidine β-sulfoxide) and monomeric sesquiterpene alkaloids (nupharidine, 7-epideoxynupharidine, nupharolutine) showed weak activity. In this review, we summarize our studies of the biofunctional effects of these alkaloids.

An Orobanchaceae plant Cistanche tubulosa (SCHENK) WIGHT (Kanka-nikujuyou in Japanese), which is one of the authorized plant resources as Cistanches Herba in both Japanese and Chinese Pharmacopoeias, is a perennial parasitic plant growing on roots of sand-fixing plants. The stems of C. tubulosa have traditionally been used for treatment of impotence, sterility, lumbago, and body weakness as well as a promoting agent of blood circulation. In recent years, Cistanches Herba has also been widely used as a health food supplement in Japan, China, and Southeast Asian countries. Here we review our recent studies on chemical constituents from the stems of C. tubulosa as well as their bioactivities such as vasorelaxtant, hepatoprotective, and glucose tolerance improving effects.

Photodynamic therapy (PDT) is a modern cancer therapy. But it is still difficult to obtain ideal photosensitizers. We synthesized six new peri-xanthenoxanthene derivatives rapidly and efficiently using solid-phase carbon-bath microwave irradiation technology, and investigated their in vitro photodynamic antitumor activity with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Our results showed that all compounds exhibited extremely low dark cytotoxicity and good phototoxicity against four human cancer cell lines. In particular, compound 3c showed the best in vitro PDT activity against Hela cells and Bel-7402 cells with IC₅₀ values of 91 and 74 nmol/L, respectively. Its value of 1-octanol/water partition coefficient (log K_ow) was 0.5309, suggesting that it is a promising photosensitizer for PDT due to its low dark cytotoxicity, high phototoxicity, and potential water solubility.

We aim to attain the sustainable use of longgu and have investigated the significance of longgu in Keishikaryukotsuboreito (KRB) decoction. We have already reported that longgu alters compound profiles in KRB decoction and hypothesized that it does so by adsorbing foreign organic compounds into its superficial pores. In the present study, we focused on the adsorbability of organic materials onto longgu surface as the cause of component profile alteration. We analyzed the physical changes in longgu through the decoction process by measuring the adsorbed water on longgu surface. ¹H magic angle spinning NMR (¹H-MASNMR) spectroscopic analysis revealed that raw longgu (R-raw) as well as decocted longgu [whether single (R-r) or KRB (R-krb) decoction] adsorbed water. However, the amount of adsorbed water in R-krb was smaller than that in R-raw and R-r. The nitrogen adsorption isotherms of longgu samples indicated that longgu was macroporous. The Brunauer–Emmett–Teller (BET) surface area of R-krb was smaller than that of R-raw and R-r. Further, thermogravimetric analysis of longgu samples showed that R-krb adsorbed matter that R-raw and R-r did not adsorb. The above findings and the ¹H-MASNMR analysis of heated longgu samples suggested that longgu adsorbed organic compounds into the pores. We considered that longgu adsorbed organic compounds during KRB decoction into its superficial pores through the decoction process.

In our search for novel orally active α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, we found that conversion of an allyl group in the lead compound 2-[allyl(4-methylphenyl)amino]-4H-pyrido[3,2-e][1,3]thiazin-4-one (4) to a 2-cyanoethyl group significantly increased inhibitory activity against AMPA receptor-mediated kainate-induced toxicity in rat hippocampal cultures. Here, we synthesized 10 analogs bearing a 2-cyanoethyl group and administered them to mice to evaluate their anticonvulsant activity in maximal electroshock (MES)- and pentylenetetrazol (PTZ)-induced seizure tests, and their effects on motor coordination in a rotarod test. 3-{(4-Oxo-4H-pyrido[3,2-e][1,3]thiazin-2-yl)[4-(trifluoromethoxy)phenyl]amino}propanenitrile (25) and 3-[(2,2-difluoro-2H-1,3-benzodioxol-5-yl)(4-oxo-4H-pyrido[3,2-e][1,3]thiazin-2-yl)amino]propanenitrile (27) exhibited potent anticonvulsant activity in both seizure tests and induced minor motor disturbances as indicated in the rotarod test. The protective index values of 25 and 27 for MES-induced seizures (10.7 and 12.0, respectively) and PTZ-induced seizures (6.0 and 5.6, respectively) were considerably higher compared with those of YM928 (5) and talampanel (1).

Hypobromous acid (HOBr) is generated not only by eosinophils but also by neutrophils in the presence of Br⁻ at the plasma concentration. Reactivity of HOBr is greatly modulated by coexistent compounds such as amines and amides. In this study, we investigated effects of urea in the reaction of nucleosides with HOBr. When nucleosides were incubated with HOBr without urea in potassium phosphate buffer at pH 7.4 and 37°C, the reactions almost completed within 10 min, with consumptions in the order of 2′-deoxyguanosine > 2′-deoxycytidine > 2′-deoxythymidine > 2′-deoxyadenosine, generating 8-bromo-2′-deoxyguanosine and 5-bromo-2′-deoxycytidine. In the presence of urea, the reaction of nucleosides with HOBr was relatively slow, continuing over several hours. When HOBr was preincubated without urea in potassium phosphate buffer at pH 7.4 and 37°C for 48 h, the preincubated HOBr solution did not react with nucleosides. However, a similar preincubated solution of HOBr with urea reacted with nucleosides to generate 8-bromo-2′-deoxyguanosine and 5-bromo-2′-deoxycytidine. These results imply that a reactive bromine compound with a long life, probably bromourea, is generated by HOBr in neutral urea solution and reacts with nucleosides, resulting in brominated nucleosides.

A reverse phase (RP)-HPLC method for separation and determination of Schisandrin A and Schisandrin B was presented, using a C18 Bondclone column, with methanol–water (v/v = 68 : 32) as mobile phase at a flow-rate of 1.00 mL·min⁻¹, and UV detection at 220 nm. The tested parameters included mobile phase composition and UV detection wavelength. Good linearities were observed within concentration ranges of Schisandrin A 0.008–4.8 mg·L⁻¹ (r = 0.9996), and Schisandrin B 0.005–3.1 mg·L⁻¹ (r = 0.9994), respectively. The limit of detection (LOD) (S/N = 3) were 0.005 mg·L⁻¹ Schisandrin A and 0.002 mg·L⁻¹ Schisandrin B, respectively. The method was applied to determine the 2 compounds in a traditional Chinese medicine preparation for treatment of hepatic diseases, Huganpian tablet. To eliminate matrix effect, Oasis hydrophilic lipophilic balance (HLB) solid-phase extraction (SPE) was used to purify the ultra-sonicately extracted solution of the drug sample. Combined with the HLB SPE purification procedure, the HPLC method gave satisfactory results for quantitation of Schisandrin A and Schisandrin B in 3 types of Huganpian tablet samples, with spiking recoveries ca. 98% (relative standard deviation (R.S.D.) ≤ 3.5%) (n = 5).

This study demonstrates the relation between the redox properties and cytotoxicity of anthraquinone derivatives with a hydroxyl and methoxy group. The redox behavior of the anthraquinone derivatives was initially observed via cyclic voltammetry and their characteristics were investigated using molecular orbital calculations. The cytotoxicity of the anthraquinone derivatives was then evaluated using human leukemia HL-60 and H₂O₂ resistant HP100 cells, and its correlation with the redox properties of these compounds was investigated. Therefore, it was suggested that the anthraquinone derivatives express cytotoxicity through H₂O₂ production, and that generation of the oxidized radical form influences their cytotoxicity.

Two novel cucurbitane glycosides, named as 11-oxomogroside III A₁ and 7β-methoxy-mogroside V, along with sixteen known ones were isolated from the fruits of Siraitia grosvenori SWINGLE. The structures of the new compounds were characterized by chemical and extensive spectral methods.

Eighteen novel chalcone derivatives containing indole and naphthalene moieties (2–19) were synthesized and characterized by ¹H-NMR, ¹³C-NMR and high resolution (HR)-MS spectra. All compounds were evaluated for their in vitro cytotoxic potential against human hepatocellular carcinoma (HepG2), human colon carcinoma (HCT116) and human breast adenocarcinoma (MCF-7) cell lines. Among them, compound 2, 3, 4 and 7 showed potent activities against tested cancer cell lines. More significantly, compound 7 exhibited the most potent cytotoxic activity against HepG2, HCT116 and MCF-7 with IC₅₀ values of 0.65, 1.13 and 0.82 µM, respectively. Furthermore, flow cytometry analysis indicated that compound 7 arrested cancer cells in G2/M phase. The compound 7 also displayed significant inhibition of tubulin polymerization (IC₅₀ = 3.9 µM). Finally, molecular docking studies were performed to explore the possible interactions between compound 7 and tubulin binding pockets.

Intramolecular Büchner reaction of 1-diazo-5-phenylpentan-2-ones followed by oxidation with SeO₂ or O₂ in the presence of silica gel regioselectively gave 8-formyl-1-tetralones or one-carbon-lacking 1-tetralones, respectively.