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991.
Hai‐Yang Liu Shi‐Jin Li Yi Zhao Wei Ni Xiao‐Jiang Hao Jun‐Zhu Li Yan Hua Bai‐Bo Xie Chen Qing Chang‐Xiang Chen 《Helvetica chimica acta》2007,90(10):2017-2023
Four new podocarpane‐type trinorditerpenenes, (5β,10α)‐12,13‐dihydroxypodocarpa‐8,11,13‐trien‐3‐one ( 1 ), (5β,10α)‐12‐hydroxy‐13‐methoxypodocarpa‐8,11,13‐trien‐3‐one ( 2 ), (5β,10α)‐13‐hydroxy‐12‐methoxypodocarpa‐8,11,13‐trien‐3‐one ( 3 ), and (3α,5β,10α)‐13‐methoxypodocarpa‐8,11,13‐triene‐3,12‐diol ( 4 ), together with four known diterpenes, 12‐hydroxy‐13‐methylpodocarpa‐8,11,13‐trien‐3‐one ( 5 ), spruceanol ( 6 ), ent‐3α‐hydroxypimara‐8(14),15‐dien‐12‐one ( 7 ), and ent‐3β,14α‐hydroxypimara‐7,9(11),15‐triene‐12‐one ( 8 ), were isolated from the twigs and leaves of Aleurites moluccana. Their structures were elucidated by means of comprehensive spectroscopic analyses, including NMR and MS. Except 8 , all compounds were evaluated for their cytotoxicity; compound 4 exhibited moderate inhibitory activity against Raji cells with an IC50 value of 4.24 μg/ml. 相似文献
992.
Two new ent‐abietane diterpenoids, macrophynin E ( 1 ) and macrophynin F ( 2 ), and a known related ent‐abietanoid (?)‐lambertic acid ( 3 ), together with four known ent‐kauranoids, were isolated from the roots and aerial parts of Isodon macrophylla, respectively. The structures of the new compounds were elucidated on the basis of spectroscopic‐data analysis and chemical correlations. 相似文献
993.
Wei Y Kannappan K Flynn GW Zimmt MB 《Journal of the American Chemical Society》2004,126(16):5318-5322
The morphology of monolayers formed upon adsorption of prochiral 1,5-substituted anthracene derivatives on highly oriented pyrolytic graphite is investigated using scanning tunneling microscopy at the liquid-solid interface. The adsorption orientation of these prochiral anthracene derivatives positions one of their enantiotopic faces in contact with the graphite. The molecules adsorb in rows with contact between adjacent anthracenes. The anthracene side chains extend perpendicular to the direction of the row repeat. All molecules within a single row adsorb via the same enantiotopic face. Anthracenes with side chains containing an even number of non-hydrogenic atoms (C, S) form monolayers in which molecules in adjacent rows adsorb via opposite enantiotopic faces. Anthracenes with side chains that contain an odd number of non-hydrogenic atoms form two-dimensional chiral domains in which all rows contain molecules adsorbed via the same enantiotopic face. This chain length effect on monolayer morphology represents a generalized example of structural effects previously observed in alkanoic acid monolayers formed on HOPG. The variation of the STM current with position in the vicinity of the anthracenes indicates that the highest occupied molecular orbital is the predominant mediator of tunneling for the aromatic group. 相似文献
994.
通过分子设计, 用过量丁二酸酐将单硬酯酸甘油酯的两个羟基转变为羧基, 再以辛酸亚锡为催化剂, 二苯醚为共沸脱水剂, 使其进一步与不同分子量的端羟基聚乙二醇在负压下共沸脱水偶联, 成功地制备了一系列AB2星型杂臂共聚物, 并采用1H NMR、XRD、DSC、FTIR和偏光显微镜等手段对产物及其结晶行为进行了研究. 1H NMR测试结果表明, 所得聚合物是以二丁二酸甘油酯为核, 一条硬酯酸烷基(GMS)臂和两条聚乙二醇(PEG)臂构成的AB2星型杂臂共聚物[GMS-(SA-PEG)2]. DSC和XRD测试结果表明, 在GMS-(SA-PEG)2中, GMS臂和PEG臂都能结晶; GMS臂的存在不仅影响PEG臂的结晶速度, 同时也影响其结晶的完善程度, 导致结晶温度和结晶熔融温度发生变化; GMS臂相对含量越大, 对PEG结晶行为的影响也越大. 利用偏光显微镜对结晶过程的在线观察结果表明, GMS-(SA-PEG)2的结晶形貌不同于线型聚乙二醇的大球晶, 其先形成细碎的束状晶核, 然后逐步出现生长中的球晶结构, 最后所形成的晶体尺寸有大幅度的减小, 而且其形貌和PEG臂的分子量密切相关. 可见AB2星型杂臂共聚物的结晶是先由GMS臂结晶形成小晶核, 然后再诱导PEG臂球晶的生长. 杂臂的引入对于控制星型多臂共聚物的晶形、晶貌具有重要意义. 相似文献
995.
Wei Zhang 《Tetrahedron》2007,63(43):10569-10575
CH2ClF has been found to be a useful electrophilic monofluoromethylating agent for a variety of O-, S-, and N-nucleophiles. The reaction is not sensitive to the radical scavenger such as nitrobenzene, which strongly supports an SN2 mechanism rather than an SET mechanism. Although most of these products (fluoromethyl ethers, sulfides, and amines) can be isolated with good purity, some of these compounds do intend to decompose (via defluorination) during storage. The electrophilic monofluoromethylation of carbon-nucleophiles was attempted with CH2ClF, CH2FI, or FCH2OTs as monofluoromethylating agents, but with no success. 相似文献
996.
A new pyrenemethylamine substituted l-Boc-tyrosine derivative was synthesized and characterized. UV-vis, FL, CD, and light scattering experiments proved that the chiral molecules were able to self-assemble for formation of new aggregate structure. The SEM and AFM images indicated that the helical wires could be fabricated by π-π stacking interaction between adjacent pyrene molecules. 相似文献
997.
Three new neolignans, named 1‐deoxycarinatone ( 1 ), isodihydrocarinatidin ( 2 ), and isolicarin A ( 3 ), together with the known neolignan (+)‐dehydrodiisoeugenol ( 4 ), were isolated from mace (the aril of Myristica fragrans Houtt .). Their structures were elucidated as 2‐[(1S)‐2‐(4‐hydroxy‐3‐methoxyphenyl)‐1‐methylethyl]‐6‐methoxy‐4‐(prop‐2‐enyl)phenol ( 1 ), 4‐[(2R,3R)‐2,3‐dihydro‐7‐methoxy‐3‐methyl‐5‐(prop‐2‐enyl)benzofuran‐2‐yl]‐2‐methoxyphenol ( 2 ), and 4‐{(2S,3R)‐2,3‐dihydro‐7‐methoxy‐3‐methyl‐5‐[(1E)‐prop‐1‐enyl]benzofuran‐2‐yl}‐2‐methoxyphenol ( 3 ) on the basis of spectroscopic data. 相似文献
998.
An operationally simple oxidative methyl esterification of primary alcohols in good yields using an iodine‐mediated poly[4‐(diacetoxyiodo)styrene] in methanol at room temperature is described. The polymeric reagent can be regenerated and reused as an environmentally benign reagent. 相似文献
999.
1000.
The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy. 相似文献