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31.
Morikawa T Sun B Matsuda H Wu LJ Harima S Yoshikawa M 《Chemical & pharmaceutical bulletin》2004,52(10):1194-1199
A new beta-carboline-type alkaloidal glycoside, glucodichotomine B, four new neolignan glycosides, dichotomosides A, B, C, and D, and a new phenylpropanoid glycoside, dichotomoside E, were isolated from a Chinese natural medicine, the roots of Stellaria dichotoma L. var. lanceolata. The structures of the new glycosides were determined on the basis of chemical and physicochemical evidence. Among them, dichotomoside D inhibited the release of beta-hexosaminidase (IC(50)=64 microM) as well as tumor necrosis factor-alpha and interleukin-4 (IC(50)=16, 34 microM) in RBL-2H3 cells. These findings suggest that dichotomoside D is more effective against the late-phase reactions in type I allergy than in the immediate phase. 相似文献
32.
Shinichi Yamabe Noriko Tsuchida Tsutomu Minato Takahisa Machiguchi 《Theoretical chemistry accounts》2005,113(2):95-106
Cheletropic additions forming cyclopropane rings were studied theoretically. Ten addition paths were traced by means of density-functional-theory calculations. Two 1,4-dienes, 1,4-pentadiene, and tricyclo[5.3.1.04,9]undeca-2,5-diene were adopted as substrates. CO, SO2, C2H5PCl2, CCl2 and SiCl2 were employed as cheletropic reagents (Xs). An orbital correlation diagram of the Woodward–Hoffmann (W–H) rule and frontier molecular orbital (FMO) interactions between them were investigated in detail. The FMO interactions, HOMO (1,4-diene)lumo (X) and homo (X)LUMO (diene), work reasonably for the progress of the reactions. Those cause the formation of two C–X bonds and a cyclopropane ring, and alternation of double bonds to single bonds. All the additions are concerted. The easiness of the ring formation depends upon the energy gap between HOMO and lumo and that between homo and LUMO, and the spatial directions of HOMO and LUMO extensions. Symmetry conservation of the W–H rule does not hold necessarily for those addition paths. The symmetry-breaking was discussed in terms of FMO interactions.Acknowledgement This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan and by Nishida Memorial Foundation for Fundamental Chemical Research. 相似文献
33.
Masaki Hasegawa Kazuhiko Saigo Hirokazu Katsuki Noriyuki Yonezawa Toshio Kanoe 《Journal of polymer science. Part A, Polymer chemistry》1983,21(8):2345-2362
The ring-opening polyaddition reaction of anti and syn head-to-head Coumarin dimers with diamines and the photocleavage behavior of the resulting polyamides were investigated. Anti head-to-head Coumarin dimer successfully reacted with aliphatic and aromatic diamines in an aprotic polar solvent to give corresponding high molecular weight polyamides. The polyamides showed good film forming ability and exhibited solubility behavior typical of polyelectrolytes. Furthermore, these polyamides were found to undergo exclusively asymmetric photocleavage on the cyclobutane rings in the polymer main chain to give a fumaramide unit with elimination of 2,2′-dihydroxystilbene. On the other hand, syn head-to-head Coumarin dimer gave only low molecular weight polyamides. These polymerization and photocleavage behaviors were elucidated in comparison with those of model reactions. 相似文献
34.
Hiroshi Nishikawa Ei-Ichi Terada Eishun Tsuchida Yoshimi Kurimura 《Journal of polymer science. Part A, Polymer chemistry》1978,16(10):2453-2463
The (alkyl)-bis(dimethylglyoximato)pyridinecobalt attached to polychloromethylstyrene by a cobalt–carbon bond was prepared by the reaction of Co(II)(DH)2Py with polychloromethylstyrene in benzene. The fraction of p-vinylbenzyl·Co(DH)2Py introduced to the polymer was 8.1 and 2.1 mole %. The photodecomposition of the polymer-bonded cobaloxime was investigated by following the change of the visible spectrum. The rate constant kdec of the polymer-bonded cobaloxime was 1.1 × 10?2 sec?1 in benzene; it is one-fourth of that of its monomeric analog, benzyl·Co(DH)2Py. The kdec values of the cobaloximes were also measured in benzene–dimethyl sulfoxide mixed solvents, and the polymer effects were discussed. The dependence of the photodecomposition on energy of the irradiation light was investigated, and it was found that the absorption band near 470 nm is important for the photodecomposition of the cobalt–carbon bond. Spectroscopic measurements of the ligand exchange reaction of polymer-bonded cobaloxime with pyridine in dimethyl sulfoxide gave a larger equilibrium constant (1.2 × 104 liter/mole) than that of benzyl·Co(DH)2Py (9.4 × 102 liter/mole). The kinetic data of the ligand exchange reaction indicated that the larger equilibrium constant for the polymeric system is due to the smaller rate constant of the reverse reaction. The thermodynamic parameters were also obtained. 相似文献
35.
First asymmetric total synthesis of tetrodotoxin 总被引:3,自引:0,他引:3
Tetrodotoxin, a toxic principle of puffer fish poisoning, is one of the most famous marine natural products because of the complex structure having many functional groups and its potent biological activity leading to death. Since the structure elucidation in 1964, this toxin has been recognized as a formidable target molecule for total synthesis. We have recently achieved the first asymmetric total synthesis from 2-acetoxy-tri-O-acetyl-d-glucal as a chiral starting material. The highly hydroxylated cyclohexane ring was constructed by Claisen rearrangement and regioselective hydroxylations of an acetone moiety and an intramolecular directed aldol condensation of the precursor having methyl ketone with dihydroxyacetone, which was synthesized through Sonogashira coupling. Installation of nitrogen functionality was unsuccessful through an attempted Overman rearrangement. We, therefore, employed a new intramolecular conjugate addition strategy between the carbamate and unsaturated ester groups. The alpha-hydroxyl lactone moiety was synthesized through an intramolecular epoxide opening by the Z-enolate of aldehyde, which was followed by oxidation-reduction of the resulting cyclic vinyl ether. The lactone was then converted to a protected ortho ester, and then gunanidinylation was followed by cleavage of the 1,2-glycol to give the fully protected tetrodotoxin. Selection of the protective groups has finally led us to accomplish the total synthesis of tetrodotoxin in an enantiomerically pure form. All the stereogenic centers were controlled with high selectivity, and the hydroxyl groups were differently protected to discriminate for the future analogue synthesis of a bioorganic program. The synthetic tetrodotoxin was purified by ion exchange chromatography and characterized to be identical with the natural compound. 相似文献
36.
Mitsunori Honda Yuichi Yamamoto Hideki Tsuchida Masahito Segi Tadashi Nakajima 《Tetrahedron letters》2005,46(38):6465-6468
Treatment of cyclopropylsilylmethanols derived from cyclopropyl silyl ketones with acid catalyst gives the corresponding silyl-substituted homoallyl derivatives in high yields with good stereoselectivity, independent of the substituents on the cyclopropyl ring. Cyclopropylsilylmethanols having a n-, s-butyl or phenyl group on the carbinyl carbon react to afford the E-homoallyl derivatives selectively. On the other hand, the reaction of cyclopropylsilylmethanols having a tert-butyl group gives Z-isomers exclusively. The following protiodesilylation of the resulting homoallyl derivatives proceeds with retention of configuration. 相似文献
37.
Oguchi T Tozuka Y Hanawa T Mizutani M Sasaki N Limmatvapirat S Yamamoto K 《Chemical & pharmaceutical bulletin》2002,50(7):887-891
The solid-state complexation between cholic acid (CA) and either methyl p-hydroxybenzoate (MPB) or ibuprofen (IBP) was investigated. Powder X-ray diffractometry, IR spectroscopy and thermal analysis suggested the complex formation between CA and MPB as well as between CA and IBP by co-grinding method. The stoichiometry of CA-MPB was 1 : 1 while that of CA-IBP was 2 : 1, reflecting the effect of guest size on complex formation. The guest compounds were assumed to be included in the channel of complexes formed by hydrogen bonds among CA molecules. 相似文献
38.
The organic acids in the urine and serum of diabetic patients with ketoacidosis and disturbance of consciousness were studied using acidification, extraction, evaporation, methoxime formation and trimethylsilylation, gas chromatographic separation and mass spectrometric identification procedures. The organic acid profile of 1 ml of serum ultrafiltrate was obtained with good separation using a gas chromatograph equipped with a glass capillary column and a splitless injector. 5-Hydroxyhexanoic acid and 3-hydroxyvaleric acid were identified for the first time in the urine of diabetic patients with ketoacidosis. Urinary excretion and serum concentrations of 2,3-dideoxypentonic acid were increased in diabetic patients. 相似文献
39.
Hiroshi Tachimori Toshio Masuda 《Journal of polymer science. Part A, Polymer chemistry》1995,33(12):2079-2085
1-(p-N-Carbazolylphenyl)-2-phenylacetylene (p-CzDPA) was polymerized by TaCl5–co-catalyst systems (cocatalysts: n-Bu1Sn, Et3SiH, and 9BBN) to produce acetone-insoluble polymers in about 60-70% yields. Poly(p-CzDPA) was a yellowish-orange solid, most part of which was soluble in toluene, chloroform, etc., and its weight-average molecular weights were around 4×105. This polymer formed a tough film by solution casting, and was thermally very stable (the onset temperature of weight loss in TGA in air 470°C). The oxygen per-meability coefficient of the polymer at 25°C was lower than two barrers. The present polymer showed photoconductivity and redox activity. © 1995 John Wiley & Sons, Inc. 相似文献
40.
Itoh T Shichi T Yui T Takahashi H Inui Y Takagi K 《The journal of physical chemistry. B》2005,109(8):3199-3206
The present study is an investigation of a reversible thermal color change induced in lamella hybrids of poly(diacetylenecarboxylates) incorporated in layered double hydroxide (LDH) nanosheets. These poly-[m,n]/LDH hybrids prepared by the photo- or gamma-ray-induced polymerization of diacetylenecarboxylates, i.e., CH(3)(CH(2))(m)()(-)(1)CC-CC(CH(2))(n)()(-)(1)CO(2)(-) (mono-[m,n]), and intercalated in LDH lamella sheets, were observed to develop colors ranging from yellow to blue. The change in color was found to depend greatly on the alkyl carbon numbers of the mono-[m,n] (m,n = 10,11; 5,11; 10,5; 16,1) values. Moreover, the conformational alignment of the mono-[m,n] within the LDH was observed to be a crucial factor in color development, which was greatly affected by the intercalation degrees and extent of poly(ene-yne) linkage elongation of the polymers. For the poly-[m,n]/LDH hybrids investigated, a reversible color change was found to occur repeatedly and remarkably for the poly-[10,11]/LDH hybrid. This color change occurred at temperatures between ca. 20 and 80 degrees C back and forth from purple red to bright orange, in stark contrast to the irreversible color change for poly-[10,11] without LDH. Moreover, DSC and Raman spectroscopic studies of the LDH hybrids showed that the thermochromic temperature corresponded to the phase transition temperature of 80 degrees C. XRD analysis also indicated that the poly-[m,n]/LDH hybrid could retain its lamella structure during such thermochromic color changes, enabling conformational recovery in the polymer chains by a cooling down of the hybrids to temperatures lower than the transition temperature, while the nonhybrid poly-[10,11] powders exhibited an irreversible color change at 60 degrees C, above which the polymer powder turned amorphous. 相似文献