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31.
Jia‐Jian Wang Hua‐Ming Zeng Zhi‐Gang She Cheng‐Du Miao Kui Hong Yu‐Cheng Gu Lan Liu Yong‐Cheng Lin 《Helvetica chimica acta》2011,94(10):1875-1880
Two new meroterpenes, ‘acetoxydehydroaustin B’ ( 1 ) and ‘1,2‐dihydro‐acetoxydehydroaustin B’ ( 2 ) were isolated in the form of a mixed crystal from the mangrove endophytic fungus Aspergillus sp. 085241B. Their structures and absolute configurations were determined by extensive analysis of their spectra and X‐ray diffraction data. In a preliminary bioassay, the mixed crystal did not exhibit activities against cancer cell lines of MDA‐MB‐435, SKBR3, HepG2, HEP3B, PC‐3, and A549, as well as against α‐glucosidase and tyrosinase. 相似文献
32.
Du‐Qiang Luo Wen‐Liang Zhu Xiao‐Long Yang Shu‐Juan Liang Zhi‐Ran Cao 《Helvetica chimica acta》2010,93(6):1209-1215
Two new daphniphyllum alkaloids named 2‐hydroxyyunnandaphnine D ( 1 ) and methyl 7‐hydroxyhomodaphniphyllate ( 2 ), together with eight known alkaloids, daphnioldhanin D, calyciphylline F, calyciphylline B, deoxycalyciphylline B, daphnicyclidin H, macropodumine C, 9,10‐epoxycalycine A, and yunnandaphnine A, were isolated from the stems and leaves of Daphniphyllum calycinum. Their structures and relative configurations were established on the basis of spectral evidence (including 2D‐NMR) and subsequently confirmed by a single‐crystal X‐ray crystallographic diffraction analysis. 相似文献
33.
34.
层状钢筋混凝土结构常见的裂缝、层间离缝等损伤具有尺度小、隐蔽的特点,常规检测方法无法对其精确查明与定量评价。以高铁层状无砟轨道结构为研究对象,使用阵列式超声装备采集半矩阵数据,利用全聚焦算法对轨道内部结构及损伤成像,通过线性旅行时插值射线追踪算法计算超声波在层状介质中传播的最短到达时间代入全聚焦成像公式,具有深度准确、分辨率高、聚焦性好的特点。提出一种层间密实度评价方法,以表面超声直达波能量为基准分析反射波能量差异计算密实指数,可定量分析无砟轨道层间状态。文中层状介质的检测和层间损伤定量评价方法有效查明层状无砟轨道层内裂缝和层间离缝,对使用超声波检测层状结构及层间损伤具有借鉴意义。 相似文献
35.
Some recently described pentapeptides containing the α,α‐disubstituted α‐amino acids Aib and Phe(2Me) have been cyclized in DMF solution using diphenyl phosphorazidate (DPPA), O‐(1H‐benzotriazol‐1‐yl)‐N,N,N′,N′‐tetamethyluronium tetrafluoroborate/1‐hydroxybenzotriazole (TBTU/HOBt), and diethyl phosphorocyanidate (DEPC), respectively, to give the corresponding cyclopentapeptides in fair‐to‐good yields. In the case of peptides with L ‐amino acids, and (R)‐ and (S)‐Phe(2Me), the yields differed significantly in favor of the L /(R) combination. The conformations in the crystals of cyclo(Gly‐Aib‐(R,S)‐Phe(2Me)‐Aib‐Gly) and cyclo(Gly‐(R)‐Phe(2Me)‐Pro‐Aib‐Gly) have been determined by X‐ray crystallography, leading to quite different results. In the latter case, the conformation in solution has been elucidated by NMR studies. 相似文献
36.
Four new Aib‐containing cyclopentapeptides have been synthesized by cyclization of the corresponding linear pentapeptides using the diethyl phosphorocyanidate (DEPC)/EtN(iPr)2 method. The linear precursors were prepared via the ‘azirine/oxazolone method’, i.e., the Aib units were introduced by the reaction of amino acids or peptide acids with a 2,2‐dimethyl‐2H‐azirin‐3‐amine, followed by selective hydrolysis of the terminal amide function. Most remarkably, cyclo[(Aib)5] exists in CDCl3 solution in a symmetrical conformation, i.e., no intramolecular H‐bonds are detectable. 相似文献
37.
Jong Sam Jeon 《Linear algebra and its applications》2011,435(5):1147-1156
Let A be an n×n irreducible ray or sign pattern matrix. If A is a sign pattern, it is shown that either A is powerful or else Ak has an ambiguous entry for some , and further, sign patterns based on the Wielandt graph show that this bound is the best possible. If A is a ray pattern, partial results for the same bound are given. 相似文献
38.
Two new ent‐kaurane diterpenes, wedelidins A ( 8 ) and B ( 9 ), together with eighteen other constituents, including the sesquiterpenoids 1 and 2 , ent‐kaurane diterpenes 3 – 7 , triterpenoids 10 and 11 , steroids 12 – 14 , and flavonoids 15 – 17 as well as benzene derivatives 18 – 20 , were isolated from the aerial parts of Wedelia trilobata. The structures of wedelidins A ( 8 ) and B ( 9 ) were elucidated by extensive spectroscopic analyses (including UV, IR, NMR, and MS). Furthermore, the structures of compounds 2 and 3 were confirmed by X‐ray single‐crystal diffraction analyses. 相似文献
39.
Jean Rodolphe Chouna Pepin Alango Nkeng‐Efouet Bruno Ndjakou Lenta Jean Duplex Wansi Beate Neumann Hans‐Georg Stammler Samuel Fon Kimbu Norbert Sewald 《Helvetica chimica acta》2011,94(6):1071-1076
Two new endiandric acid derivatives, beilschmiedic acid F ( 1 ) and beilschmiedic acid G ( 2 ), together with three known constituents, beilschmiedic acid A, beilschmiedic acid C, and sitosterol 3‐β‐D ‐glucopyranoside, were isolated from the stem bark of Beilschmiedia anacardioides. Their structures were elucidated mainly by using a combination of 1D‐ and 2D‐NMR techniques. The structure and relative configuration of beilschmiedic acid G ( 2 ) was also confirmed by X‐ray crystallographic analysis. 相似文献
40.
Michael A. Shestopalov Olga A. Efremova Anton I. Smolentsev Yuri V. Mironov Vladimir E. Fedorov Yong‐Won Song 《Helvetica chimica acta》2011,94(10):1786-1791
A new germanium complex, cis‐[Ge(pyca)2(OH)2]?2 H2O ( 1 ; pyca=pyridine‐2‐carboxylato), was synthesized by the reaction of [Ge(acac)2Cl2] (acac=acetylacetonato=pentane‐2,4‐dionato) with potassium pyridine‐2‐carboxylate (Kpyca) in H2O/THF. According to the single‐crystal X‐ray diffraction analysis, each Ge‐atom of 1 is coordinated by two pyca ligands and two OH? groups (Fig. 1). These molecules are bonded to each other via a system of H‐bonds resulting in a sheet‐like structure (Fig. 2). The complex is decomposed during heating with stepwise mass loss and formation of GeO2 as final product (Fig. 3). 相似文献