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91.
92.
Singh SB Ball RG Bills GF Cascales C Gibbs JB Goetz MA Hoogsteen K Jenkins RG Liesch JM Lingham RB Silverman KC Zink DL 《The Journal of organic chemistry》1996,61(22):7727-7737
Farnesyl-protein transferase (FPTase) is an enzyme responsible for the farnesylation of Ras protein. Farnesylation is required for cell-transforming activity in several tumor-types, and therefore, inhibition of FPTase activity may be a potential target for anticancer drugs. Our continued search for novel inhibitors led to the isolation of a number of bicyclic resorcinaldehyde cyclohexanone derivatives named here cylindrols A(1) to A(4), cylindrols B and B(1), and a number of known compounds, from Cylindrocarpon lucidum. The compounds were isolated by bioassay-guided separation using Sephadex LH-20, silica gel, and reverse phase HPLC. Structures were elucidated by extensive application of 2D NMR and X-ray crystallography. The determination of absolute stereochemistry was accomplished by CD measurements. Chemical transformations of the most abundant compound resulted in a number of key derivatives which were critical for the evaluation of structure activity relationship. These compounds are members of ascochlorin family and showed a wide range of inhibitory activity (0.7 &mgr;M to >140 &mgr;M) against FPTase. The FPTase activity was noncompetitive with respect to both substrates. Isolation, structures, chemical transformations, and FPTase activity are discussed in detail. 相似文献
93.
The synthesis of tetracyclic polyhydroxyquinones 5a and 5b was achieved through a sequence involving two Diels-Alder reactions with 1-methoxy-1,3-cyclohexadiene: the first with 2-(p-tolylthio)naphthazarin and the second on the resulting tricyclic derivative previously transformed into a (p-tolylsulfinyl)naphthazarin. The success of this strategy stemmed from the efficient remote regiocontrol exerted by the thioether substituent in the first step. 相似文献
94.
B. Gutsche und R. Herrmann 《Fresenius' Journal of Analytical Chemistry》1968,242(1):13-17
Zusammenfassung Die in einer vorangegangenen Arbeit beschriebene Methode zur Bestimmung von chlorhaltigen Insecticiden in Extrakten aus tierischen und menschlichen Nahrungsmitteln wird durch folgende Maßnahmen wesentlich vereinfacht: a) Statt eines Spektralphotometers für den flammenspektrophotometrischen Nachweis wird ein einfaches Filterflammenphotometer verwandt. b) Das vorangegangene Extraktionsverfahren wird durch Weglassen eines Extraktionsschrittes wesentlich vereinfacht. Die Nachweisgrenzen der Methode und die Wiederauffindungsraten werden durch dieses Vorgehen sogar verbessert.
Die Arbeit wurde mit Mitteln der Deutschen Forschungsgemeinschaft unterstützt. 相似文献
Flame -spectrophotometric determination of pesticides with a filter-photometer
In a preceding paper a flamespectrophotometric method for the analysis of chlorinated pecticides in extracts of animal and human food-stuffs was described. Now this method was simplified by using a flame photometer with filters instead of a photometer with monochromators and by omission of one extraction step. In spite of these simplifications the detection limits are improved and a better recovery is obtained.
Die Arbeit wurde mit Mitteln der Deutschen Forschungsgemeinschaft unterstützt. 相似文献
95.
Michael MuehlhoferThomas Strassner Eberhardt HerdtweckWolfgang A Herrmann 《Journal of organometallic chemistry》2002,660(2):121-126
Novel bridged platinum(II) biscarbene complexes are reported: 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) (3) and 1,1′-dimethyl-3,3′-ethylene-4-diimidazolin-2,2′-diylidene platinum(II) complexes 4 are directly accessible in high yields starting from platinum halides. The one-pot synthesis obviates the need for multi-step reactions via metal precursors or free carbenes. An X-ray crystal structure of 1,1′-dimethyl-3,3′-methylene-4-diimidazolin-2,2′-diylidene platinum(II) dibromide (3b) confirmed the structural similarity to the known corresponding palladium complexes. Since free 1,1′-di-R-3,3′-methylene-4-diimidazolin-2,2′-diylidenes are only available in low yields this synthetic route provides an easy access to the corresponding carbene complexes. 相似文献
96.
Carmen R. Alonso-Cruz Francisco J. Ortiz-López Ernesto Suárez 《Tetrahedron letters》2005,46(32):5265-5268
The reaction of derivatives of 3-acetyl-d-glucal, 3-acetyl-l-rhamnal, 3-acetyl-d-galactal, and 3-acetyl-d-lactal with sodium benzenesulfinate in acid medium catalyzed by HgSO4 afforded diastereoisomeric mixtures of the corresponding 2,3-dideoxy-3-(phenylsulfonyl)-hexopyranoses through a Ferrier rearrangement. The anomeric alkoxyl radical fragmentation of these γ-hydroxy sulfones using the system (diacetoxyiodo)benzene and iodine gave vinyl sulfones with structures of 1,2-dideoxy-4-O-formyl-2-(phenylsulfonyl)-pent-1-enitol and configurations d-erythro, l-erythro, and d-threo at the two stereogenic centers. 相似文献
97.
Alkaloids such as cinchonidine, quinine and N-methylephedrine have been N-alkylated using polymeric benzyl halides or co-polymerized and then N-alkylated, thus affording a series of polymer-supported chiral ammonium salts which have been employed as phase-transfer catalysts in the asymmetric benzylation of an N-(diphenylmethylene)glycine ester. These new polymeric catalysts can be easily recovered by simple filtration after the reaction and reused. The best ee's were achieved when Merrifield resin-anchored cinchonidinium ammonium salts were employed. 相似文献
98.
Coupled-column liquid chromatography with fluorescence detection was applied to the determination of o-phenylphenol and bitertanol residues in orange and banana fruits. After extraction with a mixture of acetone, dichloromethane-petroleum ether, and ethyl acetate, an extract aliquot of 100 microL was injected directly without any additional clean-up into the chromatographic system using two reversed phase C18 coupled columns. The LC-LC approach allowed automated sample clean up of the vegetal extracts, leading to a simple and rapid analytical procedure, with limits of quantification between 0.01 and 0.05 mg kg(-1). Recovery experiments performed on orange and banana samples fortified at different concentrations (0.01 - 4 mg kg(-1)) gave average recoveries between 70 and 113% with relative standard deviations lower than 15%. The procedure developed was finally applied to orange and banana samples from different geographical locations and the results were confirmed by GC-MS. 相似文献
99.
Galan MC Venot AP Glushka J Imberty A Boons GJ 《Journal of the American Chemical Society》2002,124(21):5964-5973
It is demonstrated that conformationally restricted oligosaccharides can act as acceptors for glycosyltransferases. Correlation of the conformational properties of N-acetyl lactosamine (Galbeta(1-4)GlcNAc, LacNAc) and several preorganized derivatives with the corresponding apparent kinetic parameters of rat liver alpha-(2,6)-sialyltransferase-catalyzed sialylations revealed that this enzyme recognizes LacNAc in a low energy conformation. Furthermore, small variations in the conformational properties of the acceptors resulted in large differences in catalytic efficiency. Collectively, our data suggest that preorganization of acceptors in conformations that are favorable for recognition by a transferase may improve catalytic efficiencies. 相似文献
100.
Armbruster P Agarwal YK Brüchle W Brügger M Dufour JP Gaggeler H Hessberger FP Hofmann S Lemmertz P Münzenberg G Poppensieker K Reisdorf W Schadel M Schmidt K Schneider JH Schneider WF Sümmerer K Vermeulen D Wirth aG Ghiorso A Gregorich KE Lee D Leino M Moody KJ Seaborg GT Welch RB Wilmarth P Yashita S Frink C Greulich N Herrmann G Hickmann U Hildebrand N Kratz JV Trautman N Fowler MM Hoffman DC Daniels WR von Gunten HR Dornhöfer H 《Physical review letters》1985,54(5):406-409