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81.
Structural Features of a Polysaccharide from Centella asiatica 总被引:3,自引:0,他引:3
Xue Song WANG Jin You DUAN Ji Nian FANG* Shanghai Institute of Materia Medica Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai 《中国化学快报》2004,15(2):187-190
Centella asiatica has been used as remedy for sodation, stabilization and against lepra, anabrosis1 in the oriental countries. The low-molecular-weight constituents in Centella asiatica have been investigated1. However, no polysaccharides have been reported. 1BI was the first polysaccharide isolated from C. asiatica, which had immunostimulating activity in vitro. In present study, we report the structural features of 1BI. Experimental Extraction, isolation and purification Dried C.… 相似文献
82.
3,4—二硫方酸的从头算研究 总被引:2,自引:2,他引:2
在6-31G°水平上对3,4-二硫方酸(3,4-二巯基-3-环丁烯-1,2-二酮)的3种平面构象异构体进行SCF计算,结果表明,ZZ型异构体最稳定,XE型次之,从等键反应能量分析,3,4-二太酸的稳定性,与苯作探讨其芳香性,关在6-31G水平上计算了3种构象的振动频率。 相似文献
83.
84.
Yan Wu LI Liang HUANG* Institute of Materia Medica Chinese Academy of Medical Sciences & Peking Union Medical College Beijing 《中国化学快报》2002,13(10)
The natural product, hainanolide 1, also under the name harringtonolide2 demonstrated antitumor and antiviral activities in preliminary test. Its structure was determined by X-ray diffraction. The total synthesis of 1 was reported recently by Mander3. A different scheme of its synthesis has been studied in our laboratory4. Here the determination of the stereochemical structure of the key intermediate 2 in the synthesis was reported. HMBC and HMQC spectra identified the skeleton and H,… 相似文献
85.
Xiao Long WANG Jian Peng FENG Xin Gang XIE Xiao Ping CAO* Xin Fu PAN* Department of Chemistry & State Key Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2004,(9)
Aiphanol was isolated from the seeds of Aiphanes aculeate Willd. (Arecaceae) collected in Peru and was reported to exhibit significant inhibitory activities against cyclooxyge- nases-1 and -2. The structure of aiphanol was elucidated by spectroscopic methods as an unprecedented stilbenolignan skeleton in which a stilbene moiety is linked to a phenylpropane unit through a dioxane bridge1. In our previous works the synthetic approach to 1,4-benzodioxane lignans were achieved2. Since aiphanol… 相似文献
86.
A systematic quantum chemical characterization of intrinsic structure, energies and spectral properties of all the studied cross-link adducts formed by the novel trans platinum with thiazole ligand has been carried out at B3LYP/6-31G^* level of theory with the Lanl2dz pseudo potential basis set for the Pt atom. Special attention has been paid to the relative stability of these complexes and the factors that probably alter the order of the relative stability. The important influence of hydrogen bond on the structures, the energies and the spectral property was revealed. Other factors that contribute to relative stability including solvation effect, entropy and electronic delocalization energy were taken into account. The stability energy of the whole complex, and the interaction energy between two purine bases and the [Pt-(NH3)thiazole]^2+ group were adopted to study the interplay among subsystems and their contribution to relative stability of all the studied cross-link model. Finally, basic spectral properties of these complexes including H(8) chemical shifts of all the studied complexes and the VCD (vibrational circular dichroism) spectra of two pairs of GG chelate enantiomers, were provided in order to define the structure of the most possible duplex bearing novel trans platinum drug lesions. 相似文献
87.
88.
Polymer-supported reagents for organic synthesis are enjoying a renewed popularity with the emergence of combinatorial chemistry in recent years1. 4-(Arylseleno)morpholines formed in situ are useful -seleno-introducing reagents for saturated aldehydes2. -Sele- noaldehydes, as a frequently used intermediates, can be converted into -haloaldehydes by halogenating reaction3. However, organic selenium reagents always have a foul smell and are quite toxic, which is often problematic in organic sy… 相似文献
89.
在B3LYP/6-31G(d,p)水平,全优化Mg2+、Ca2+、Mn2+、Co2+、Zn2+、Cu2+、Ni2+、Cd2+ (用有效实势(ECP) 方法处理)与腺嘌呤(A) N(1)、N(7)位点配位的两类配合物气相结构,通过相互作用能和自由能分析分别得出两位点对所研究金属离子的选择性顺序;后采用Onsager模型,优化其在水溶液(=78.39)中的结构,讨论溶剂效应对上述顺序的影响;通过相对自由能分析分别得出气相和溶液中,同种金属对两位点的选择性规律。溶液中金属离子与N(7)位配位的相对优选顺序为:Co2+ > Mg2+ > Cd2+ > Ca2+ > Zn2+ > Mn2+ > Ni2+ > Cu2+。 相似文献
90.
Yun Yan GAO Chang Jiang YOU Jin Ping CHEN Yong Yong LIU Bao Wen ZHANG Yi LI* Technical Institute of Physics Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2002,13(12)
The photochemistry of the vitamin D family and their precursors has been the subject of extensive studies for many years1-4. Most of the studies focus on the photoisomer- ization of 7-dehydrocholesterol and that of tachysterol to previtamin D3, which is of commercial importance in the synthesis of vitamin D34, 5. Recently the cis/trans isomerization of vitamin D analogs (Scheme 1) draws attention because of its importance in the synthesis of hydroxylated vitamin D metabolites6. However, o… 相似文献