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991.
[reaction: see text] Reactions of the bifunctional allylstannane 2-(chloromethyl)-3-(tributylstannyl)propene with aldehydes have been examined. These generally occur in high yields using Lewis acid promoters and the products can be isolated and purified without incident. Good yields and high enantioselectivities are also realized in catalytic asymmetric allylations (CAA reactions) using the previously described BITIP catalyst system. Protection of the free hydroxyl can be accomplished without cyclization to the derived tetrahydrofuran, although this transformation is also facile. The utility of the incorporated allyl chloride functionality allows for the obvious use of such products in reactions with nucleophiles. Use of these products in a less obvious connective strategy is demonstrated in the synthesis of the C12-C27 segment of bryostatin 1 where a connective, or "lynchpin", double-allylation process was employed. The beta-hydroxy allyl chloride obtained from an initial chelation-controlled allylation of aldehyde 16 was converted to allylstannane 19 and applied in a second allylation reaction, thus allowing for a highly convergent synthesis of the bryostatin C ring backbone in a stereoselective fashion. 相似文献
992.
Han QB Lee SF Qiao CF He ZD Song JZ Sun HD Xu HX 《Chemical & pharmaceutical bulletin》2005,53(8):1034-1036
From the antibacterial fraction of the roots of Garcinia kola, 3',4',4',5,5',7,7'-heptahydroxy-3,8'-biflavanone (GB1) was isolated as the major constituent, whose interesting conformations were studied on the basis of its 1D and 2D NMR spectra obtained at different temperatures and in different solvents. GB1 showed antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) with MIC of 32 and 128 microg/ml, respectively. 相似文献
993.
本文用~(13)C-NMR研究了异戊二烯(IP)在均相催化剂(CF_3CO_2)_2LnCl·EtOH—(i-Bu)AlH—o-C_6D_4Cl_2作用下的聚合过程。单体首先被活化同稀土配位生成η~4-IP稀土配合物(反式和顺式),然后η~4-IP的C-3和C-4插入Ln-H键生成η~3-烯丙基稀土配合物——η~3-(2-甲基)丁烯基稀土配合物(同式和对式)。二维~(13)C-NMR交换谱表明η~4-IP和0η~3-烯丙基的每对异构体在常温下分别进行慢交换反应(互变异构),这一过程使插入反应在常温下得以进行。 相似文献
994.
Yuan Yang Jinnan Zhang Surong Luo Xiaohong Song Qi Li 《Frontiers of Chemistry in China》2007,2(3):296-302
Two new inclusion compounds (n-C4H9)4N+C18-H13O4
−·B(OH)3 (1) and (n-C4H9)4N+C18H13O4
− (2) were prepared and characterized by X-ray crystallography. Crystal data: compound 1, monoclinic P2(1)/c, a = 1.569 9(1) nm, b = 0.995 5(6) nm, c = 2.293 3(1) nm, β = 109.962(3)°, Z = 4, and R
1 = 0.0434, wR = 0.075 9; compound 2, monoclinic C2/c, a = 1.400 5(3) nm, b = 1,282 1(2) nm, c = 1.765 7(3) nm, β = 100.388(1)°, Z = 4, and R
1 = 0.0584, wR = 0.096 6. In the crystal structure of 1, the tetramers formed by two trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (EADA) anions and two boric acid molecules were connected through
O—H⋯O hydrogen bonds to generate a channel type host lattice. The tetra-n-butylammonium cations were stacked to give two columns within each channel with cross-sectional size of about 2.30 nm × 0.93
nm. In the crystal structure of 2, similar honeycomb host lattices with big size were also formed along the [101] direction
by three-dimensional accumulation of EADA anions. The tetra-n-butylammonium cations were accommodated in a zigzag fashion within each channel.
Translated from Acta Chimica Sinica, 2006, 64(18): 1904–1910 [译自: 化学学报] 相似文献
995.
996.
Plasmonic nanoparticles (e.g., gold, silver) have attracted much attention for biological sensing and imaging as promising nanoprobes. Practical biomedical applications demand small gold nanoparticles (Au NPs) with a comparable size to quantum dots and fluorescent proteins. Very small nanoparticles with a size below the Rayleigh limit (usually <30–40 nm) are hard to see by light scattering using a dark-field microscope, especially within a cellular medium. A photothermal microscope is able to detect very small nanoparticles, down to a few nanometers, but the imaging speed is usually too slow (minutes to hours) to image living cell processes. Here an absorption modulated scattering microscopy (AMSM) method is presented, which allows for the imaging of sub-10 nm Au NPs within a cellular medium. The unique physical mechanism of AMSM offers the remarkable ability to remove the light scattering background of the cellular component. In addition to having a sensitivity comparable to that of photothermal microscopy, AMSM has a much higher imaging speed, close to the video rate (20 fps), which allows for the dynamic tracking of small nanoparticles in living cells. This AMSM method might be a valuable tool for living cell imaging, using sub-10 nm Au NPs as biological probes, and thereby unlocking many new applications, such as single molecule labeling and the dynamic tracking of molecular interactions.An absorption modulated scattering microscopy technique that allows for the imaging of sub-10 nm gold nanoparticles within a cellular scattering medium is presented. 相似文献
997.
Three new organically templated or organically bonded zinc selenates, namely, {H2bipy}Zn(SeO4)2(H2O)21 (bipy=4,4′-bipyridine), {H2pip}{Zn(SeO4)2(H2O)4}·2H2O 2 (pip=piprazine), and Zn(SeO4)(phen)(H2O)23 (phen=1,10-phenanthroline) have been synthesized by hydrothermal reactions. The structure of compound 1 features a 1D chain composed of [Zn(SeO4)2(H2O)2]2− anions. Compound 2 has a 2D layer structure built from {Zn(SeO4)2(H2O)4}2− anions that are cross-linked by doubly protonated piperazine cations via N-H?O hydrogen bonds. The structure of compound 3 contains a 1D chain of Zn(SeO4)(phen)(H2O)2, such chains are further interlinked by hydrogen bonds and π?π interactions to form a 〈200〉 layer. The different roles the templates played have also been discussed. 相似文献
998.
Ostash B Rix U Rix LL Liu T Lombo F Luzhetskyy A Gromyko O Wang C Braña AF Méndez C Salas JA Fedorenko V Rohr J 《Chemistry & biology》2004,11(4):547-555
A 3 kb DNA fragment from the Streptomyces globisporus 1912 landomycin E (LaE) biosynthetic gene cluster (lnd) was completely sequenced. Three open reading frames were identified, lndGT4, lndZ4, and lndZ5, whose probable translation products resemble a glycosyltransferase, a reductase, and a hydroxylase, respectively. Studies of generated mutants from disruption and complementation experiments involving the lndGT4 gene allowed us to determine that LndGT4 controls the terminal L-rhodinose sugar attachment during LaE biosynthesis and that LndZ4/LndZ5 are responsible for the unique C11-hydroxylation of the landomycins. Generation of the novel landomycins F, G, and H in the course of these studies provided evidence for the flexibility of lnd glycosyltransferases toward their acceptor substrates and a basis for initial structure-activity relationships within the landomycin family of antibiotics. 相似文献
999.
1000.