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61.
Juliawaty LD Kitajima M Takayama H Achmad SA Aimi N 《Chemical & pharmaceutical bulletin》2000,48(11):1726-1728
A new type of natural product, idenburgene (1), was isolated from Crytocarya idenburgensis, and its unique structure was elucidated. Four known compounds, 3-hydroxy-5-methoxystilbene (2), 2',6'-dihydroxy-4'-methoxydihydrochalcone (3), stigmast-4-ene-3-one, and beta-sitosterol were also isolated and identified. 相似文献
62.
63.
Aimi N Kitajima M Yokoya M Takayama H Sakamoto S Yamaguchi K 《Chemical & pharmaceutical bulletin》2002,50(11):1528-1529
The fragmentation from beta-carboline-type monoterpenoid glucoindole alkaloids to harman, which is a hypothetical pathway to generate simple beta-carbolines, was actualized in the collision-induced dissociation in MS. 相似文献
64.
Lead tetraacetate oxidation of a Corynanthe-type indole alkaloid, mitragynine, produced mainly 7-acetoxyindolenine derivative (2) together with a dimeric compound (4) as a minor product. The novel structure having a bridge between the C-11' and C-7 positions in the respective indolenine parts and its formation mechanism were studied. 相似文献
65.
66.
Mariko Kitajima Satoko Ohara Noriyuki Kogure Dammrong Santiarworn Hiromitsu Takayama 《Tetrahedron》2013
Six new β-carboline-type indole alkaloid glycosides, ophiorrhisides A–F (1–6), were isolated from Ophiorrhiza trichocarpon (Rubiaceae) collected in Thailand. Ophiorrhisides A (1) and B (2) possess a lactam function in the C ring and a unique biose residue in the molecule. Ophiorrhiside F (6) has a highly oxidized C ring with a 1,2-dicarbonyl function at C-5 and C-6 positions as well as a double bond between C-3 and C-14. 相似文献
67.
The absolute configuration of pandamarilactonine-A, a pyrrolidine alkaloid, was established on the basis of total synthesis starting from l-prolinol. An insight into the mechanism of the low enantiomeric purity of natural pandamarilactonine-A is discussed. 相似文献
68.
Tomohiro Hirano Hiroko Kitajima Satoshi Ishii Makiko Seno Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2005,43(17):3899-3908
The radical polymerization of N‐isopropylacrylamide (NIPAAm) in toluene at low temperatures was investigated in the presence of triisopropyl phosphate (TiPP). The addition of TiPP induced a syndiotactic specificity that was enhanced by the polymerization temperature being lowered, whereas atactic polymers were obtained in the absence of TiPP, regardless of the temperature. Syndiotactic‐rich poly(NIPAAm) with a racemo dyad content of 65% was obtained at ?60 °C with a fourfold amount of TiPP, but almost atactic poly(NIPAAm)s were obtained by the temperature being lowered to ?80 °C. This result contrasted with the result in the presence of primary alkyl phosphates, such as tri‐n‐propyl phosphate: the stereospecificity varied from syndiotactic to isotactic as the polymerization temperature was lowered. NMR analysis at ?80 °C revealed that TiPP predominantly formed a 1:1 complex with NIPAAm, although primary alkyl phosphates preferentially formed a 1:2 complex with NIPAAm. Thus, it was concluded that a slight increase in the bulkiness of the added phosphates influenced the stoichiometry of the NIPAAm–phosphate complex at lower temperatures, and consequently a drastic change in the effect on the stereospecificity of NIPAAm polymerization was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3899–3908, 2005 相似文献
69.
Sakihito Kitajima 《Photochemistry and photobiology》2008,84(6):1404-1409
Reactive oxygen species (ROS), such as the superoxide anion and hydrogen peroxide, are generated by the photosystems because photoexcited electrons are often generated in excess of requirements for CO2 fixation and used for reducing molecular oxygen, even under normal environmental conditions. Moreover, ROS generation is increased in chloroplasts if plants are subjected to stresses, such as drought, high salinity and chilling. Chloroplast‐localized isoforms of ascorbate peroxidase and possibly peroxiredoxins assume the principal role of scavenging hydrogen peroxide. However, in vitro studies revealed that both types of peroxidases are easily damaged by hydrogen peroxide and lose their catalytic activities. This is one contributing factor for cellular damage that occurs under severe oxidative stress. In this review, I describe mechanisms of hydrogen peroxide‐mediated inactivation of these two enzymes and discuss a reason why they became susceptible to damage by hydrogen peroxide. 相似文献
70.
Hossain MK Shimada T Kitajima M Imura K Okamoto H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(17):9241-9244
Spatial distribution of surface enhanced Raman activity is visualized for two-dimensional (2D) nearly close-packed and well-ordered monolayer array of gold nanoparticles by using scanning near-field optical microscope. The 2D arrays exhibit highly nonuniform enhancement in Raman scattering, i.e., the regions along the edge of the 2D array are preferentially enhanced. We demonstrate that the spatial distribution of the localized electric field is also nonuniform and agrees well with that of the Raman enhancement. 相似文献