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191.
Shota Kato Daichi Mizukami Tomoya Sugai Masashi Tsuda Haruhiko Fuwa 《Chemical science》2021,12(3):872
Amphirionin-2 is a linear polyketide metabolite that exhibits potent and selective cytotoxic activity against certain human cancer cell lines. We disclose herein the first total synthesis of amphirionin-2 and determination of its absolute configuration. Our synthesis featured an extensive use of cobalt-catalyzed Mukaiyama-type cyclization of γ-hydroxy olefins for stereoselective formation of all the tetrahydrofuran rings found in the natural product, and a late-stage Stille-type coupling for convergent assembly of the entire carbon backbone. Four candidate diastereomers of amphirionin-2 were synthesized in a unified, convergent manner, and their spectroscopic/chromatographic properties were compared with those of the authentic material. The present study culminated in the reassignment of the C5/C7 relative configuration, assignment of the C12/C18 relative configuration, and determination of the absolute configuration of amphirionin-2.An extensive application of cobalt-catalyzed Mukaiyama-type cyclization of γ-hydroxy olefins and a late-stage Stille-type reaction enabled syntheses of four diastereomers of amphirionin-2 to establish its absolute configuration. 相似文献
192.
Kenichi Miyata Ryuji Tamamushi Haruhiko Taguchi Kohji Seio Mitsuo Sekine 《Tetrahedron letters》2004,45(51):9365-9368
Modified oligodeoxynucleotides incorporating 4-N-(N-arylcarbamoyl)-dC derivatives 1a-c were synthesized. The 1H NMR spectra of 1a-c suggest that the carbamoyl group forms an intramolecular hydrogen bond with the cytosine ring nitrogen atom so that formation of a Watson-Crick base pair with the complementary guanine base is inhibited. The hybridization properties of oligodeoxynucleotides containing 1a-c were investigated by use of Tm analysis. The hybridization properties of 4-N-(N-phenylcarbamoyl)-dC (1a) were similar to those of 4-N-(N-alkylcarbamoyl)-dC derivatives reported previously. In sharp contrast to 1a, it turned out that 4-N-(N-napht-1-yl) and (N-quionol-5-yl)-dC (1b,c) have a unique property as a universal base. 相似文献
193.
Haruhiko Ohya Takeshi Onodera Masahiko Aihara Youichi Negishi 《Journal of membrane science》1996,110(2):249-252
By a method of laser firing, a high zirconia containing (70%) composite membrane on porous ceramic tubing was successfully fabricated. The laser sintered composite membrane was characterized by gas separation/permeation experiments. In the separation experiment of a CO2---CH4 gaseous mixture, it was found that the separation factor of CH4 over CO2 was 1.15. In the pure gases permeation experiment, it was found that Knudsen diffusion is considered to be predominant in the permeation mechanism for pure gases H2, He, CH4, N2, O2, and CO2, and the permeation mechanism of H2O at lower temperature depends mainly on surface diffusion and on Knudsen diffusion at higher temperature. 相似文献
194.
Nine novel sulfate-type hybrid surfactants, CmF2m+1C6H4CH(OSO3Na)CnH2n+1 (FmPHnOS: m=4, 6, 8; n=3, 5, 7; C6H4: p-phenylene), with a benzene ring in their molecules were synthesized. Alkanoyl chlorides were allowed to react with iodobenzene in the presence of aluminum chloride to give the corresponding aromatic ketones. The reaction of the ketones with perfluoroalkyl iodides yielded 1-[4-(perfluoroalkyl)phenyl]-1-alkanones as intermediates. The intermediates were allowed to react with methanol in tetrahydrofuran in the presence of sodium borohydride to yield 1-[4-(perfluoroalkyl)phenyl]-1-alkanols. The desired hybrid surfactants were obtained by the reaction of 1-[4-(perfluoroalkyl)phenyl-1-alkanols with sulfur trioxide/pyridine complex in pyridine and by the subsequent neutralization of the products with sodium hydroxide solution. When compared with the conventional hybrid surfactants, CmF2m+1C6H4COCH(SO3Na)CnH2n+1 (FmHnS: m=4, 6; n=2, 4, 6; C6H4: p-phenylene), the new hybrid surfactants thus synthesized were found to have a comparable ability to lower the surface tension of water and a high hydrophilicity. The cmc of FmPHnOS obeyed Kleven’s rule and their occupied areas per molecule increased with increasing m and n with the values between 0.66 and 1.05 nm2. The aggregation number for FmPHnOS micelles ranged from 6 to 45 and the hydrodynamic radius of the micelles was in the range of 1.4-3.1 nm. 相似文献
195.
[reaction: see text] A new route to N-unprotected deoxynucleoside 3'-phosphoramidite building blocks by use of highly selective N-deacylation of commercially available N-acylated deoxynucleoside 3'-phosphoramidites is described. These compounds could be readily converted to other types of N-protected species by facile N-acylations with acylating reagents. 相似文献
196.
Noriko?FujiwaraEmail author Daisaku?Yoshihara Haruhiko?Sakiyama Hironobu?Eguchi Keiichiro?Suzuki 《Hyperfine Interactions》2016,237(1):114
NMR active nuclei, 1H, 13C and 15N, are usually used for determination of protein structure. However, solution 17O-NMR application to proteins is extremely limited although oxygen is an essential element in biomolecules. Proteins are oxidized through cysteine residues by two types of oxidation. One is reversible oxidation such as disulphide bonding (Cys-S-S-Cys) and the other is irreversible oxidation to cysteine sulfinic acid (Cys-SO 2H) and cysteine sulfonic acid (Cys-SO 3H). Copper,Zinc-superoxide dismutase (SOD1) is a key enzyme in the protection of cells from the superoxide anion radical. The SH group at Cys 111 residue in human SOD1 is selectively oxidized to -SO 2H and -SO 3H with atmospheric oxygen, and this oxidized human SOD1 is also suggested to play an important role in the pathophysiology of various neurodegenerative diseases, probably mainly via protein aggregation. Therefore, information on the structural and the dynamics of the oxidized cysteine residue would be crucial for the understanding of protein aggregation mechanism. Although the -SO 3H group on proteins cannot be directly detected by conventional NMR techniques, we successfully performed the site-specific 17O-labeling of Cys 111 in SOD1 using \(^{17}\textit {O}_{2}\) gas and the 17O-NMR analysis for the first time. We observed clear 17O signal derived from a protein molecule and show that 17O-NMR is a sensitive probe for studying the structure and dynamics of the 17O-labeled protein molecule. This novel and unique strategy can have great impact on many research fields in biology and chemistry. 相似文献
197.
X-ray diffraction study of supercooled water has been performed using an imaging-plate X-ray detector down to −15 °C. The peak at 10.8 Å, which grows with decreasing temperature, in the radial distribution function {D(r) − 4πr2ρ0} indicates the existence of clathrate-like structures in supercooled water. It is suggested that anomalous properties of water, which become more pronounced at low temperatures, are closely linked to the development of clathrate-like structures in water at low temperatures. 相似文献
198.
Total synthesis of (-)-brevenal, a novel marine polycyclic ether natural product, is described. Highly efficient and scalable entries to the AB-ring exo-olefin and the DE-ring enol phosphate and a rapid construction of the C-ring by means of our Suzuki-Miyaura coupling-based strategy realized a concise synthesis of the pentacyclic skeleton of (-)-brevenal. The present synthesis is considerably more efficient than our previous synthesis (longest linear sequence: 50 steps from 2-deoxy-d-ribose). 相似文献
199.
Marine polycyclic ether natural products continue to fascinate chemists and biologists due to their exceptionally large and complex molecular architectures and potent and diverse biological activities. Tremendous progress has been made over the past decade toward the total synthesis of marine polycyclic ether natural products. In this area, a convergent strategy for assembling small fragments into an entire molecule always plays a key role in successful total synthesis. This review describes our efforts to develop convergent strategies for the synthesis of polycyclic ethers and their application to the total synthesis of gambierol, gymnocin-A, and brevenal, and to the partial synthesis of the central part of ciguatoxins and the nonacyclic polyether skeleton of gambieric acids. 相似文献
200.
Cytosine and adenine N-oxide derivatives have long been known as products resulting from the oxidative damage of DNA by peroxides such as hydrogen peroxide. Although the synthesis and properties of 2'-deoxynucleoside N-oxide derivatives have been well described, little has been reported about the chemical and biochemical behavior of initially formed DNA oligomers containing these N-oxide bases. In this study, we established a convenient method for the solid-phase synthesis of oligodeoxynucleotides incorporating 2'-deoxycytidine N-oxide (dC O) or 2'-deoxyadenosine N-oxide (dA O) by using the postsynthetic oxidation of N-protected DNA oligomers except for the target dC or dA site with m-CPBA in MeOH in a highly selective manner. In this strategy, the benzoyl, phthaloyl, and (4-isopropylphenoxy)acetyl groups proved to serve as base protecting groups to avoid oxidation of adenine, cytosine, and guanine, respectively, at the unmodified sites. 相似文献