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排序方式: 共有91条查询结果,搜索用时 15 毫秒
1.
Zhifang Xi Wei Bie Wei Chen Dong Liu Leen van Ofwegen Peter Proksch Wenhan Lin 《Helvetica chimica acta》2013,96(12):2218-2227
Six new biscembranoids, namely, sarcophytolides G–L ( 1 – 6 , resp.), together with six known analogs, were isolated from a marine soft coral Sarcophyton elegans. The structures of the new compounds were established on the basis of 1D‐ and 2D‐NMR (COSY, HSQC, HMBC, and NOESY) spectroscopic analysis together with the aid of MS, CD, and IR data. The unusual isobiscembranoid sarcophytolide G ( 1 ) was found for the first time in the genus Sarcophyton. 相似文献
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Malgorzata Basko Melania Bednarek Leen Billiet Przemyslaw Kubisa Eric Goethals Filip Du Prez 《Journal of polymer science. Part A, Polymer chemistry》2011,49(7):1597-1604
A straightforward strategy for the synthesis and functionalization of polyurethanes (PUs) via the use of alkyne‐functionalized polytetrahydrofuran (PTHF) diols is described. The alkyne groups have been introduced into the PTHF chains by the cationic ring‐opening copolymerization of tetrahydrofuran and glycidyl propargyl ether. These PTHF prepolymers were combined with 1,4‐butanediol and hexamethylene diisocyanate for the synthesis of linear PUs with latent functionalization sites. The polyether segments of the PUs have then been coupled with several types of functionalized azides by the copper‐catalyzed azide‐alkyne “click” chemistry, for example with phosphonium containing azides for their antibacterial properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
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Wei Cheng Ming Ji Xiaodan Li Jinwei Ren Fuling Yin Leen van Ofwegen Siwang Yu Xiaoguang Chen Wenhan Lin 《Tetrahedron》2017,73(17):2518-2528
Chemical investigation of the gorgonian coral Junceella fragilis resulted in the isolation of a new norditerpenoid fragilolide A (1), sixteen new briarane diterpenoids fragilolides B-Q (2–17), together with frajunolides H and N, and three known norcembranoids scabrolide D, sinuleptolide and 5-epi-sinuleptolide. The structures of new compounds were determined on the basis of extensive spectroscopic analysis, including the experimental and calculated ECD data and single-crystal X-ray diffraction for the configurational assignments. The structure of fragilolide A featured an unprecedented 4,13- and 7,11-fused tetracyclic norcembranoid, while the biogenetic relationships of the briarane analogues were postulated. Frajunolide H exerted significant inhibition against a panel of tumor cell lines, and six briarane diterpenoids (3, 6, 8, 12, 16, and frajunolide N) exhibited the inhibitory effects against the HBeAg express of hepatitis B virus in HepAD38 cells. In addition, sinuleptolide and 5-epi-sinuleptolide exerted the effects to inhibit NO production in RAW264.7 macrophage cells, in addition to the activation of ARE and the inhibition of NF-κB expression. 相似文献
6.
Volker Leen Dr. Wenwu Qin Prof. Dr. Wensheng Yang Jie Cui Chan Xu Xiaoliang Tang Dr. Weisheng Liu Prof. Dr. Koen Robeyns Dr. Luc Van Meervelt Prof. David Beljonne Prof. Dr. Roberto Lazzaroni Prof. Dr. Claire Tonnelé Noël Boens Prof. Wim Dehaen Prof. 《化学:亚洲杂志》2010,5(9):2016-2026
Starting from the conformationally unconstrained compound 3,5‐di‐(2‐bromophenoxy)‐4,4‐difluoro‐8‐(4‐methylphenyl)‐4‐bora‐3a,4a‐diaza‐s‐indacene ( 1 ), two BODIPY dyes ( 2 and 3 ) with increasingly rigid conformations were synthesized in outstanding total yields through palladium catalyzed intramolecular benzofuran formation. Restricted bond rotation of the phenoxy fragments leads to dyes 2 and 3 , which absorb and fluoresce more intensely at longer wavelengths relative to the unconstrained dye 1 . Reduction of the conformational flexibility in 2 and 3 leads to significantly higher fluorescence quantum yields compared to those of 1 . X‐ray diffraction analysis shows the progressively more extended planarity of the chromophore in line with the increasing conformational restriction in the series 1 → 2 → 3 , which explains the larger red shifts of the absorption and emission spectra. These conclusions are confirmed by quantum chemical calculations of the lowest electronic excitations in 1 , 1a , 2 , 2a , 3 and dyes of related chemical structures. The effect of the molecular structure on the visible absorption and fluorescence emission properties of 1 , 1a , 2 , 2a , 3 has been examined as a function of solvent by means of the new, generalized treatment of the solvent effect (J. Phys. Chem. B 2009 , 113, 5951–5960). Solvent polarizability is the primary factor responsible for the small solvent‐dependent shifts of the visible absorption and fluorescence emission bands of these dyes. 相似文献
7.
Rüdiger Schultz Leen Stougie Maarten H. van der Vlerk 《Mathematical Programming》1998,83(1-3):229-252
In this paper we present a framework for solving stochastic programs with complete integer recourse and discretely distributed right-hand side vector, using Gröbner basis methods from computational algebra to solve the numerous second-stage integer programs. Using structural properties of the expected integer recourse function, we prove that under mild conditions an optimal solution is contained in a finite set. Furthermore, we present a basic scheme to enumerate this set and suggest improvements to reduce the number of function evaluations needed. 相似文献
8.
Willem K. Klein Haneveld Leen Stougie Maarten H. van der Vlerk 《Annals of Operations Research》1996,64(1):67-81
We consider the objective function of a simple integer recourse problem with fixed technology matrix and discretely distributed right-hand sides. Exploiting the special structure of this problem, we devise an algorithm that determines the convex hull of this function efficiently. The results are improvements over those in a previous paper. In the first place, the convex hull of many objective functions in the class is covered, instead of only one-dimensional versions. In the second place, the algorithm is faster than the one in the previous paper. Moreover, some new results on the structure of the objective function are presented. 相似文献
9.
In practical problem situations data are usually inherently unreliable. A mathematical representation of uncertainty leads to stochastic optimization problems. In this paper the complexity of stochastic combinatorial optimization problems is discussed. Surprisingly, certain stochastic versions of NP-hard determinstic combinatorial problems appear to be solvable in polynomial time. 相似文献
10.
Daowan LaiYongxin Li Minjuan XuZhiwei Deng Leen van OfwegenPeiyuan Qian Peter ProkschWenhan Lin 《Tetrahedron》2011,67(33):6018-6029
Chemical examination of a Chinese soft coral Sinularia rigida resulted in the isolation and characterization of 19 new cembrane-type diterpenoids, designated as sinulariols A-S (1-19). Their structures were determined on the basis of extensive spectroscopic (2D NMR, IR, and MS) analysis in association with modified Mosher’s method. All compounds featured unusual 19-oxygenated functionalities, which are rarely found from cembranoid family. The biogenetic transformation of the isolated compounds is postulated. Part of the isolated cembranoids showed significant anti-fouling activity. 相似文献