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101.
Hamasaki T Kashiwagi T Imada T Nakamichi N Aramaki S Toh K Morisawa S Shimakoshi H Hisaeda Y Shirahata S 《Langmuir : the ACS journal of surfaces and colloids》2008,24(14):7354-7364
There are few reports on the physiological effects of metal nanoparticles (nps), especially with respect to their functions as scavengers for superoxide anion radical (O2(.-)) and hydroxyl radical (.OH). We tried to detect the scavenging activity of Pt nps using a hypoxanthine-xanthine oxidase system for O2(.-) and using a Fenton and a UV/H2O2 system for .OH. Electron spin resonance analysis revealed that 2 nm particle size Pt nps have the ability to scavenge O2(.-) and .OH. The calculated rate constant for the O2(.-)-scavenging reaction was 5.03 +/- 0.03 x 10(7) M (-1) s (-1). However, the analysis of the Fenton and UV/H 2O 2 system in the presence of Pt nps suggested that the .OH-scavenging reaction cannot be determined in both systems. Among particle sizes tested from 1 to 5 nm, 1 nm Pt nps showed the highest O2(.-)-scavenging ability. Almost no cytotoxicity was observed even after adherent cells (TIG-1, HeLa, HepG2, WI-38, and MRC-5) were exposed to Pt nps at concentrations as high as 50 mg/L. Pt nps scavenged intrinsically generated reactive oxygen species (ROS) in HeLa cells. Additionally, Pt nps significantly reduced the levels of intracellular O2(.-) generated by UVA irradiation and subsequently protected HeLa cells from ROS damage-induced cell death. These findings suggest that Pt nps may be a new type of antioxidant capable of circumventing the paradoxical effects of conventional antioxidants. 相似文献
102.
Morikawa T Xie H Wang T Matsuda H Yoshikawa M 《Chemical & pharmaceutical bulletin》2008,56(10):1438-1444
From the methanolic extract of the whole plant of Sinocrassula indica (Crassulaceae), six new flavonol glycosides, sinocrassosides B(4) (1), B(5) (2), C(1) (3), D(1) (4), D(2) (5), and D(3) (6), were isolated together with 30 compounds. The structures of 1-6 were elucidated on the basis of chemical and physicochemical evidence. In addition, several constituents were found to show inhibitory effects on aminopeptidase N and aldose reductase. 相似文献
103.
Tsukasa Nakahodo Midori O. Ishitsuka Yutaka Maeda Hisashi Fujihara Takeshi Akasaka 《Tetrahedron letters》2008,49(14):2302-2305
The photochemical reaction of C60 with selenium-containing bicyclooctanes affords for the first time the selenylfullerenes. The derivatives were characterized by mass, UV-vis absorption, NMR spectroscopy, and X-ray crystallographic analysis. 相似文献
104.
Satoshi Nagao Ayaka Suda Hisashi Kobayashi Naoki Shibata Yoshiki Higuchi Shun Hirota 《化学:亚洲杂志》2020,15(11):1743-1749
Domain swapping is an exception to Anfinsen's dogma, and more than one structure can be produced from the same amino acid sequence by domain swapping. We have previously shown that myoglobin (Mb) can form a domain‐swapped dimer in which the hinge region is converted to a helical structure. In this study, we showed that domain‐swapped dimerization of Mb was achieved by a single Ala mutation of Gly at position 80. Multiple Ala mutations at positions 81 and 82 in addition to position 80 facilitated dimerization of Mb by stabilization of the dimeric states. Domain swapping tendencies correlated well with the helical propensity of the mutated residue in a series of Mb mutants with amino acids introduced to the hinge region. These findings demonstrate that a single mutation in the hinge loop to modify helical propensity can control oligomer formation, providing new ideas to create high‐order protein oligomers using domain swapping. 相似文献
105.
Kanno K Igarashi E Zhou L Nakajima K Takahashi T 《Journal of the American Chemical Society》2008,130(17):5624-5625
Selective synthesis of linear trienes from three different alkynes was achieved in one-pot procedure using the Zr/Cu system. Zirconacyclopentadiene prepared from two different alkynes such as an alkyl-substituted alkyne and an aryl-substituted alkyne reacted with NCS gave chlorodienylzirconocene. It reacted with the third alkyne with electron-withdrawing groups in the presence of CuCl to afford the corresponding linear triene. 相似文献
106.
Kazuhiro Kobayashi Hiroyasu Takeuchi Shinzo Seko Yoshikazu Kanno Sachiko Kujime Hiroshi Suginome 《Helvetica chimica acta》1993,76(8):2942-2950
The 2,3-dihydro-1H-benz[f]indole-4,9-diones 3a–d , h were formed in a one-step reaction in 13–82% yield by an unprecedented [3 + 2] regioselective photoaddition of 2-amino-1,4-naphthoquinone ( 1 ) with various electronrich alkenes 2 (Scheme 1, Table). The [3 + 2] photoadducts derived from 1 with vinyl ethers and vinyl acetate gave 1H-benz[f]indole-4,9-diones 4e , f , i , in 33–72% yield, by spontaneous loss of the corresponding alcohol or AcOH from the resulting adducts; 4i has a kinamycin skeleton. The [3 + 2] photoaddition also took place on irradiation of the differently substituted amino-1,4-benzoquinones 6 , 7 , and 12 and excess alkenes 2 in benzene, giving 1H-indole-4,7-dione derivatives 13 and 14 (Scheme 3), 15a and 16 (Scheme 4), and 18 (Scheme 4), respectively. The initial products in these photoadditions were proved to be hydroquinones, the air oxidation of which yielded the heterocyclic quinones; 2,3-dihydro-2-methoxy-2-methyl-5-phenyl-1H-indole-1,4,7-triyl triacetate ( 19 ) was isolated after treatment of the crude photoaddition mixture obtained from 2-amino-5-phenyl-1,4-benzoquinone ( 7 ) and 2-methoxyprop-1-ene ( 2f ) with Ac2O and pyridine under N2. A pathway leading to the annelated hydroquinones involving ionic intermediates arising from an electron transfer in these photoadditions is proposed (Scheme 5). 相似文献
107.
Toshio Morikawa Osama Bashir Abdel-Halim Hisashi Matsuda Osamu Muraoka Masayuki Yoshikawa 《Tetrahedron》2006,62(26):6435-6442
Three new pseudoguaiane-type sesquiterpenes, dichrocepholides A-C, and two new pseudoguaiane-type sesquiterpene dimers, dichrocepholides D and E, were isolated from the aerial part of Dichrocephala integrifolia. Their stereostructures were determined on the basis of chemical and physicochemical evidence. In addition, the extract and its principal sesquiterpene constituent, parthenin, showed an inhibitory activity on nitric oxide (NO) production and on induction of inducible NO synthase. 相似文献
108.
Highly diastereoselective polycyclization of homo(polyprenyl)arene analogues bearing terminal siloxyvinyl groups was catalyzed by tin(IV) chloride (10 mol %). The cyclizations of tert-butyldiphenylsilyl and triisopropylsilyl polyenol ethers gave 4alpha(equatorial)- and 4beta(axial)-siloxypolycycles as major isomers, respectively. The strong nucleophilicity of pro-C(9), a (6E) geometry, and a bulky silyl group effectively favored the alpha-preference, whereas the weak nucleophilicity of pro-C(9), a (6Z)-geometry, and less steric hindrance of a silyl group favored the beta-preference. [reaction: see text]. 相似文献
109.
A new bisphosphine ligand, C8-BINAP, and C8-BINAP-stabilized palladium nanoparticles have been prepared; C8-BINAP was found to be an effective protecting ligand for preparing and stabilizing palladium nanoparticles with very small core size and narrow size distribution and the C8-BINAP-Pd nanoparticles behave as an efficient catalyst for carbon-carbon coupling reactions at room temperature. 相似文献
110.
Sakurai J Oguchi T Watanabe K Abe H Kanno S Ishikawa M Katoh T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(3):829-837
Biologically important and structurally unique marine natural products avarone (1), avarol (2), neoavarone (3), neoavarol (4) and aureol (5), were efficiently synthesized in a unified manner starting from (+)-5-methyl-Wieland-Miescher ketone 10. The synthesis involved the following crucial steps: i) Sequential BF(3)Et(2)O-induced rearrangement/cyclization reaction of 2 and 4 to produce 5 with complete stereoselectivity in high yield (2 --> 5 and 4 --> 5); ii) strategic salcomine oxidation of the phenolic compounds 6 and 8 to derive the corresponding quinones 1 and 3 (6 --> 1 and 8 --> 3); and iii) Birch reductive alkylation of 10 with bromide 11 to construct the requisite carbon framework 12 (10 + 11 --> 12). An in vitro cytotoxicity assay of compounds 1-5 against human histiocytic lymphoma cells U937 determined the order of cytotoxic potency (3 > 1 > 5 > 2 > 4) and some novel aspects of structure-activity relationships. 相似文献