Kosuke Namba

Kosuke Namba
The University of Tokushima · Graduate School of Pharmaceutical Sciences

About

129
Publications
11,757
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1,481
Citations
Additional affiliations
March 2008 - April 2013
Hokkaido University
Position
  • Professor (Associate)

Publications

Publications (129)
Article
A silica-supported bifunctional heterogeneous catalytic system was developed based on imidazolium salt (Im ⁺ Clˉ@SiO 2 ) as an activator. The Im ⁺ Clˉ@SiO 2 activated both the Ag-catalyst and substrate for the carboxylative cyclization reaction of...
Article
Full-text available
Palau'amine has received a great deal of attention as an attractive synthetic target due to its intriguing molecular architecture and significant immunosuppressive activity, and we achieved its total synthesis in 2015. However, the synthesized palau'amine has not been readily applicable to the mechanistic study of immunosuppressive activity, becaus...
Article
A biaryl dimer based on eurotiumide A, a dihydroisocoumarin-type natural product possessing a 1,4-hydroquinone skeleton, was synthesized herein. The radical scavenging activity and cytotoxicity were evaluated. The prepared biaryl dimer and eurotiumide A displayed comparable potent antioxidant activities to those of α-tocopherol and edaravone. Howev...
Article
Full-text available
Iron (Fe) is an essential nutrient, but is poorly bioavailable because of its low solubility in alkaline soils; this leads to reduced agricultural productivity. To overcome this problem, we first showed that the soil application of synthetic 2′-deoxymugineic acid, a natural phytosiderophore from the Poaceae, can recover Fe deficiency in rice grown...
Article
Full-text available
Iron is an essential metal for all living organisms that is absorbed in intestinal cells as a heme-chelated or free form. It is unclear how important plant-derived chelators, such as nicotianamine (NA), an organic small molecule that is ubiquitous in crops, vegetables, and various other foods, contribute to iron bioavailability in mammals. We perfo...
Article
A concise total synthesis of tronocarpine, a chippiine-type indole alkaloid, was accomplished. The key feature of this total synthesis is one-pot construction of the pentacyclic skeleton containing an azabicyclo[3.3.1]nonane core by tandem cyclization from an indole derivative having all carbon side chains and functional groups. This tandem cycliza...
Article
A concise total synthesis of a chippiine‐type alkaloid, tronocarpine, was accomplished. The key feature of this total synthesis was construction of the key pentacyclic skeleton with an azabicyclo[3.3.1]nonane core, which required a one‐pot process including i) β‐elimination, ii) intramolecular aldol reaction, iii) six‐membered lactamization, iv) az...
Article
1,1,7,7-Tetramethyl-9-azajulolidine (TMAJ), which theoretical studies have suggested as a highly active DMAP analog, was synthesized for the first time. The catalytic activity of TMAJ was confirmed by the acetylation reactions of various tert-alcohols. TMAJ showed much higher catalytic activity than DMAP and one of the highest activity levels among...
Article
Full-text available
Side-chain derivatives of eurotiumide A, a dihydroisochroman-type natural product, have been synthesized and their antimicrobial activities described. Sixteen derivatives were synthesized from a key intermediate of the total synthesis of eurotiumide A, and their antimicrobial activities against two Gram-positive bacteria, methicillin-susceptible an...
Article
Full-text available
For the fluorescence imaging of biologically active small compounds, the development of compact fluorophores that do not perturb bioactivity is required. Here we report a compact derivative of fluorescent 1,3a,6a-triazapentalenes, 2-isobutenylcarbonyl-1,3a,6a-triazapentalene (TAP-VK1), as a fluorescent labeling reagent. The reaction of TAP-VK1 with...
Article
Asymmetric total syntheses of dihydropyran containing natural products, (+)-eurotiumide F and (+)-eurotiumide G have been described. These total syntheses revealed the absolute configuration of eurotiumide F and G, and confirmed the reported structure of eurotiumide F and revised the reported structure of eurotiumide G. Highlight of these syntheses...
Article
Asymmetric total synthesis of (+)-epilupinine was achieved in just three steps using only commercially available common reagents. The total synthesis involved alkylations of N-nosylamide, ozone oxidation, and sequential reactions of the removal of the nosyl group, intramolecular dehydrative condensation, intramolecular Mannich reaction catalyzed by...
Article
1,3a,6a‐Triazapentalene (TAP) is a compact fluorescent molecule consisting of a triazabicyclo[3.3.0]octane skeleton. In this work, a method of synthesizing a directly connected TAP ring system as a linearly bonded aromatic system with a planar form was established. The TAP‐bonded system showed interesting fluorescence properties resulting from chan...
Article
Full-text available
An organic chemistry approach to the mechanistic elucidation of iron acquisition in graminaceous plants is introduced here. To elucidate this detailed mechanism using phytosiderophores, the efficient synthesis of 2′-deoxymugineic acid (DMA), a phytosiderophore of rice, was established. The synthetic DMA was confirmed to have similar iron transport...
Article
A method of synthesizing a directly connected 1,3a,6a‐triazapentalene (TAP) ring system as a linearly bonded aromatic system with a planar form was established. Various TAP‐dimers and a 2‐alkyl‐TAP‐trimer were synthesized and their fluorescence properties were evaluated. Although the direct connection of the TAP ring with other TAP rings did not af...
Article
Introduction: It is difficult to quantify poorly soluble volatile anesthetics in aqueous solutions; this necessitates the development of alternative prompt methods to analyze the in vivo blood concentrations of anesthetics for the clinical assessment of anesthesia depth. In this study, we demonstrated that the difficulties can be overcome by using...
Article
A concise method of constructing polycyclic tropinone frameworks was developed. The single‐step synthesis of polycyclic tropinone consists of an intramolecular (4+3) cycloaddition reaction of N‐nosyl‐pyrrole with oxyallyl cation that was generated in situ by an intermolecular condensation reaction of the nucleophilic functional groups on a tethered...
Article
Asymmetric total syntheses and structure revisions of dihydroisocoumarin‐type natural products, eurotiumide A and eurotiumide B have been described. The key features of these total syntheses are the asymmetric Shi epoxidation, regio‐ and stereo‐selective epoxide opening, C1 insertion/lactonization cascade reaction for constructing 4‐methoxyisochrom...
Article
A palladium(0) nanocluster supported on hydrotalcite has been prepared and tested for the Suzuki coupling reaction. The prepared catalyst showed very efficient catalytic activity for cross coupling of iodo- and bromoarenes under very mild reaction conditions, affording >90% yield. Under the optimized reaction conditions, chloroarenenes also showed...
Article
Palau’amine has received a great deal of attention in the past two decades as an attractive synthetic target by virtue of its intriguing molecular architecture and significant immunosuppressive activity. Here, we report the total synthesis of palau’amine characterized by the Hg(OTf)2-catalyzed construction of tetra-substituted carbon center at the...
Article
1,3a,6a-Triazapentalene (TAP)-labeled enterobactin was developed as an iron ion sensor. 3-Acetylated-TAP was successfully introduced to the catechol ring of enterobactin, a well-recognized siderophore secreted by various Gram-negative bacteria. The fluorescence of TAP-labeled enterobactin decreased gradually as the amount of Fe³⁺ ion as an additive...
Article
The substituent effect at the C6-position of 1,3a,6a-triazapentalenes was elucidated. Synthesis of C6-substituted-1,3a,6a-triazapentalene was established by an epoxide-opening reaction of the 1,2,3-triazoles followed by elimination of the resulting hydroxy group. The electron-donating substituent induced a longer-wavelength shift of the fluorescenc...
Article
A palladium-catalyzed cyclization of N-tosyl imines with allylic diesters is described. The reactions of N-tosyl imines with 2-buten-1,4-diol dicarbonate and 2-methylene-1,3-propanediol diacetate afforded 2-vinyl-2,3-dihydropyrroles and 3-methylene-1,2,3,4-tetrahydropyridines, respectively.
Data
Table S1. Transmembrane topology predictions of YS1/YSL transporters and helical propensity predictions of the loop of the transporters.
Data
Fig. S1. Protein sequence alignment of YS1/YSL family transporters.
Data
Fig. S3. Schematic illustration of the Fe(III)‐DMA selectivity of HvYS1 as compared with ZmYS1 based on the helix propensity of an extracellular loop.
Data
Fig. S2. Transport activities of HvYS1, ZmYS1 and the chimeras.
Article
Full-text available
HvYS1 is a selective transporter of Fe(III)-phytosiderophores in barley that is responsible for iron acquisition from the soil. In contrast, maize ZmYS1 possesses broad substrate specificity. In this study, a quantitative evaluation of the transport activities of HvYS1 and ZmYS1 chimera proteins revealed that the seventh extracellular membrane loop...
Article
1,3a,6a-Triazapentalene is a compact fluorescent chromophore. In this study, triazapentalene was used to modify a series of biphenyl-type inhibitors of kinesin spindle protein (KSP) to develop fluorescent probes for the intracellular visualization of this protein. Microscopic studies demonstrated that these novel triazapentalene-labeled compounds e...
Article
Full-text available
Nuclear and cytoplasmic morphological changes provide important information about cell differentiation processes, cell functions, and signal responses. There is a strong desire to develop a rapid and simple method for visualizing cytoplasmic and nuclear morphology. Here, we developed a novel and rapid method for probing cellular morphological chang...
Data
Temperature-dependent cellular uptake of TAP-4PH. HL-60 cells were incubated with 50 μM TAP-4PH for 30 min at 37 or 4°C. Cellular uptake of TAP-4PH was measured by flow cytometric analysis. Data represent the mean ± S.D., n = 3. **p < 0.005, Student’s t-test. (TIF)
Data
TAP-4PH visualization of PC-12 cells. Merged bright-field and TAP-4PH fluorescent (cyan) images of PC-12 cells. (TIF)
Data
Co-staining with Golgi apparatus and ER probes in A549 cells. A549 cells were stained with a Golgi apparatus probe and ER probe, followed by treatment with 50 μM TAP-4PH for 30 min. and then observed by fluorescence microscopy. Merged image was constructed with images of TAP-4PH (cyan), Golgi apparatus probe (yellow), and ER probe (magenta). Scale...
Data
Co-staining with the nuclear staining probe acridine orange and TAP-4PH in A549 cells. Left panel, TAP-4PH; middle panel, acridine orange; right panel, merged images of TAP-4PH (cyan) and acridine orange (magenta). Scale bar: 20 μm. (TIF)
Data
TAP-4PH visualization of HL-60 cells. (a) HL-60 cells before and after differentiation into neutrophil-like cells by ATRA for 5 days. After differentiation, the cells were co-stained with Nuclear Green LSC1 for nucleus and TAP-4PH. Left panels, TAP-4PH; middle panels, Nuclear Green LSC1; right panels, merged images of TAP-4PH (cyan) and Nuclear Gre...
Data
Cell cycle analysis of HL-60 cells after incubation for 48 h in the presence (left) or absence (right) of 10 or 50 μM TAP-4PH. Data shown are representative of three independent experiments. (TIF)
Data
TAP-4PH visualization of differentiated 3T3-L1 adipocytes. 3T3-L1 cells were induced to differentiate into adipocytes for 8 days. The cells were then treated with 50 μM TAP-4PH for 30 min and observed by fluorescence microscopy. Scale bar: 10 μm. (TIF)
Data
Fluorescence emission spectra of 10 μM TAP-4PH with the indicated concentrations of DNA in PBS. (TIF)
Article
An efficient method for converting isothioureas into guanidines was developed. The use of amine salts of bis(trifluoromethanesulfonyl)imide as a nitrogen source was found to induce an efficient conversion under weak acidic conditions at 50 °C. The conversion was applicable to the various amines and carbamate-protected thioureas, and various carbama...
Article
The efficient protocol tolerates various alkenes, such as 1-substituted and 1,1-disubstituted styrene derivatives and cyclic alkenes.
Article
Full-text available
Various 2,4-disubstituted-1,3a,6a-triazapentalenes possessing methyl and phenyl groups at the C4-position were synthesized. Fluorescence observation of the synthetic 4-methyl- and 4-phenyl-1,3a,6a-triazapentalenes revealed that the introduction of a substituent at the C4-position allowed a long-wavelength shift of the fluorescence maximum. Furtherm...
Article
Palladium and boric acid-catalyzed cyclization of underivatized 1,3-diaryl propargylic alcohols with 1,3-cyclohexanediones has been developed. Boric acid plays a role for the efficient activation of the propargylic alcohols. Various substituted tetrahydrobenzofuranones were obtained in moderate to good yields. Reactions using 4-hydroxy-2-pyrones as...
Article
Oxidative radical cyclization of N-sulfonyl β-enamino esters with alkenes has been developed. Substituted 2,3-dihydropyrroles were produced when the reactions were carried out in the presence of CAN and Cu(OAc)2 as the oxidant. Intramolecular cyclization of β-enamino carbonyl compounds having an alkenyl and an alkynyl side chain proceeded to afford...
Article
Oxidative radical cyclization of 4-hydroxy-2H-chromen-2-one with aryl-substituted alkenes has been developed. 2,3-Dihydro-4H-furo[3,2-c]chromen- 4-ones having substituents at the 2-position were produced when the reactions were carried out in the presence of CAN as an oxidant. Various substituted products were regioselectively synthesized via a suc...
Article
Full-text available
Palau' amine has received a great deal of attention in the past two decades as an attractive synthetic target by virtue of its intriguing molecular architecture and significant immunosuppressive activity. Here we report the total synthesis of Palau' amine characterized by the construction of an ABDE tetracyclic ring core including a trans-bicylo[3....
Data
Supplementary Figures 1-51, Supplementary Tables 1-8, Supplementary Discussion, Supplementary Methods and Supplementary References
Article
Full-text available
Iron is an essential nutrient for all plants. However, terrestrial plants often suffer from iron deficiency in alkaline soil due to its extremely low solubility. Alkaline soil accounts for about 30% of all cultivated ground in the world. Plants have evolved two distinct strategies, I and II, for iron uptake from the soil. Dicots and non-graminaceou...
Article
Full-text available
Poaceae plants release phytosiderophores into the rhizosphere in order to chelate iron (Fe), which often exists in insoluble forms especially under high pH conditions. The impact of phytosiderophore treatment at the physiological and molecular levels in vivo remains largely elusive, although the biosynthesis of phytosiderophores and the transport o...
Article
An acid-catalyzed [4+3] cycloaddition reaction of N-nosyl pyrroles with 2-(tert-butyldimethylsilyloxy)acrolein has been developed. The reaction of 2-(silyloxy)acrolein with N-nosyl pyrrole was catalyzed by Tf2NH, and a regio- and stereoselective reaction with 2-substituted N-nosyl pyrroles leading to tropinone derivatives possessing tetra-substitut...
Article
Full-text available
Poaceae plants release 2'-deoxymugineic acid (DMA) and related phytosiderophores to chelate iron (Fe), which often exists as insoluble Fe(III) in the rhizosphere, especially under high pH conditions. Although the molecular mechanisms behind the biosynthesis and secretion of DMA have been studied extensively, little is known about whether DMA has bi...
Article
A novel strategy for the one-pot synthesis of substituted pyridines from N-arylmethyl 3-aziridinylpropiolate esters is described. The method employs a three-step procedure including the formation of allenyl imines, phosphine-catalyzed cyclization, and subsequent oxidation of the dihydropyridines. Depending on the reaction conditions of the final ox...
Article
A novel strategy for the one-pot synthesis of substituted pyridines from N-arylmethyl 3-aziridinylpropiolate esters is described. The method employs a three-step procedure including the formation of allenyl imines, phosphine-catalyzed cyclization, and subsequent oxidation of the dihydropyridines. Depending on the reaction conditions of the final ox...
Data
Effects of EDTA application on rice seedling growth at pH 8.0.
Data
Iron distribution in rice seedlings treated with DMA or EDTA for 22 h.
Data
Venn diagrams illustrating unique and overlapping genes showing more than 10-times up- or down-regulated expression compared with that in the no-chelator control at pH 5.8.
Data
Venn diagrams illustrating unique and overlapping genes up- or down-regulated more than 10-fold by indicated treatments, compared with expression in the respective tissues of control (no chelator) at pH 5.8.
Data
Transcription analysis to validate microarray analysis of gene transcription in the roots and shoots.
Data
Expression profile of iron and nitrate (nitrogen) assimilation related genes.
Data
Additional experimental procedure: microarray analysis.
Data
Full-text available
List of up-regulated genes in shoot at pH 5.8 classified in the Venn diagram shown in Figure S4. Table S2. List of down-regulated genes in shoot at pH 5.8 classified in the Venn diagram shown in Figure S4. Table S3. List of up-regulated genes in root at pH 5.8 classified in the Venn diagram shown in Figure S4. Table S4. List of down-regulated genes...
Data
Effect of chelator treatments on enzyme activity of NADH- and NADPH-dependent nitrate reductases in roots of rice seedlings.
Article
The first asymmetric total synthesis of (-)-HM-3 and (-)-HM-4, aromatic sesquiterpenes isolated from the phytopathogenic fungus Helicobasidium mompa, has been achieved. Highlight of the synthesis is an enantiospecific construction of the quaternary carbon stereocenter utilizing a palladium-catalyzed addition of arylboronic acid to the allenic alcoh...
Article
Full-text available
To expand the originally developed fluorescent 1,3a,6a-triazapentalenes as fluorescent labeling reagents, the fluorescence wavelength of 1,3a,6a-triazapentalene was extended to the red color region. Based on the noteworthy correlation of the fluorescence wavelength with the inductive effect of the 2-substituent, further electron-deficient 2-(2-cyan...
Article
New halohydrazidation and hydrazidopalladation reactions were developed that use the synthon N-acyl-N-tosylhydrazine. The intramolecular bromohydrazidation reactions of β,γ-unsaturated N-acyl-N-tosylhydrazines readily afforded pyrazolidinone ring systems that contained a tetrasubstituted carbon center, and the primary amine of the N-acyl-N-tosylhyd...
Article
Radical methods: The title reaction proceeds in the presence of a palladium catalyst to deliver substituted tetrahydrocyclobuta[b]benzofurans in a stereoselective manner. A radical mechanism is discussed.
Article
A palladium-catalyzed cyclization of β-enaminocarbonyl compounds with allylic bisacetates is described. 2-Vinyl-2,3-dihydropyrroles and 3-methylene-1,2,3,4-tetrahydropyridines were produced from the reaction of β-enaminocarbonyl compounds with 1,4-diacetoxy-2-butene and 2-methylene-1,3-propanediol diacetate, respectively.