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51.
Burke AJ Davies SG Garner AC McCarthy TD Roberts PM Smith AD Rodriguez-Solla H Vickers RJ 《Organic & biomolecular chemistry》2004,2(9):1387-1394
Conjugate addition of lithium (S)-N-benzyl-N-alpha-methylbenzylamide to a range of alpha, beta-unsaturated Weinreb amides proceeds with high levels of diastereoselectivity (>95% de). The beta-amino Weinreb amide products may be transformed into beta-amino ketones via reactions with Grignard reagents, while treatment with DIBAL-H furnishes beta-amino aldehydes. Trapping of the aldehyde via Wadsworth-Emmons reaction and subsequent manipulation offers an efficient route to homochiral delta-amino acid derivatives and 2-substituted piperidines. The application of this methodology for the synthesis of (S)-coniine is demonstrated. 相似文献
52.
Bulloch EM Jones MA Parker EJ Osborne AP Stephens E Davies GM Coggins JR Abell C 《Journal of the American Chemical Society》2004,126(32):9912-9913
(6S)-6-Fluoroshikimate has antimicrobial activity. The molecular basis of this effect had not been identified, but there was speculation that (6S)-6-fluoroshikimate is first converted in vivo into 2-fluorochorismate, which then could inhibit 4-amino-4-deoxychorismate synthase (ADCS). 2-Fluorochorismate was prepared from E-fluorophosphoenolpyruvate and erythose-4-phosphate by the sequential reactions of DAHP synthase, dehydroquinate synthase, dehydroquinase, shikimate dehydrogenase, EPSP synthase, and chorismate synthase. Inhibition studies on ADCS showed that it was inhibited rapidly and irreversibly by 2-fluorochorismate. Electrospray mass spectrometry of the inactivated enzyme showed an additional mass of 198 +/- 10 Da. A novel peptide of 1087.6 Da was identified in the HPLC trace for the tryptic digest of 2-fluorochorismate-inactivated ADCS. Sequencing of this peptide by MS/MS showed that the peptide corresponded to residues 272-279 with a modification of 206.1 Da on Lys-274. This observation is particularly exciting in the context of a recent proposal for the catalytic mechanism of ADCS. 相似文献
53.
E Bailey A G Brooks R Purchase M Meakings M Davies D G Walters 《Journal of chromatography. A》1987,421(1):21-31
An improved method has been developed for the determination of the major neutral steroids (cholesterol and 5 beta-cholestan-3 beta-ol) and unconjugated bile acids (deoxycholic acid and lithocholic acid) in human faeces, using capillary gas chromatography with flame ionization detection. The freeze-dried faecal sample was subjected to a two-stage Soxhlet extraction followed by an aqueous alkali-organic solvent partition step to separate neutral steroids from bile acids. The neutral steroids were analysed as their trimethylsilyl ether derivatives on an OV-1 capillary column. The bile acids were further purified on a Sep-Pak C18 cartridge and then fractionated on a Sep-Pak SIL cartridge. Unconjugated bile acids were analysed as their methyl ester-trimethylsilyl ether derivatives also on an OV-1 capillary column. Quantitation of neutral steroids and unconjugated bile acids was achieved by reference to appropriate internal standards, added to the faecal extract immediately after the Soxhlet extraction stage. The method is being used in a study of the effect of diet on the metabolic activity of human gut flora. 相似文献
54.
PtCl2 constitutes a convenient catalyst for intramolecular hydroalkoxylation, carboalkoxylation, hydroamination, and carboamination reactions of alkynes, effecting the formation of substituted benzo[b]furan, indole-, and isochromene-1-one derivatives, respectively. This procedure allows for the transfer of (substituted) allyl, methoxymethyl (MOM), benzyloxymethyl (BOM), and (trimethylsilyl)ethoxymethyl (SEM) groups from oxygen to carbon and is compatible with functional groups that are susceptible to oxidative insertion of low valent metal species previously used for similar purposes. Although some of the reactions can even be carried out in air, the rates are significantly increased when conducted under an atmosphere of CO. A mechanistic rationale is proposed, implying activation of the alkyne by the carbophilic Pt(2+) template as the primary step of the catalytic cycle. 相似文献
55.
Stephen G. Davies Isabelle M. Dordor Jonathan C. Walker Peter Warner 《Tetrahedron letters》1984,25(25):2709-2712
β-Hydroxy acyl ligands bound to (η5-C5H5)Fe(CO)(PPh3) are stereoselectively alkylated on the α-carbon to give after decomplexation erythro-β-hydroxy carboxylic acids. 相似文献
56.
The asymmetric synthesis of trans-substituted cyclopropanecarboxylic acid derivatives is achieved via stereoselective nucleophilic methylene transfer to E-,β-unsaturated acyl ligands bound to the iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)]. 相似文献
57.
Sevim Akyüz Tanil Akyüz J. Eric D. Davies 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(2):105-119
The adsorption of 4,4-bipyridyl by natural sepiolite and smectite group clay minerals (bentonite, hectorite and saponite) from Anatolia (Turkey) has been studied using vibrational spectroscopy. Investigation of Fourier-transform infrared and Fourier-transform Raman spectra of adsorbed 4,4-bipyridyl indicate the presence of chemisorbed species. However, any evidence for the generation of anionic species on the surface of the phyllosilicates has not been detected. It is proposed that the adsorbed bipyridyl molecules on sepiolite are centrosymmetric and H-bonded to the surface hydroxyls through both the nitrogen lone pairs as bidentate ligands. The adsorbed bipyridyl molecules on the smectite group clays are coordinated to exchangeable cations both directly and also indirectly through water as monodentate ligands. XRD patterns of the clays studied are also recorded. 相似文献
58.
D. H. Davies D. C. Phillips J. D. B. Smith 《Journal of polymer science. Part A, Polymer chemistry》1979,17(4):1153-1161
To elucidate mechanisms in electroinitiated polymerization reactions a comparison was conducted between ultraviolet (UV) photoinitiation and electroinitiation of N-vinyl phthalimide with zinc chloride as a catalyst. Both methods give low yields of a complex polymer product. A detailed analysis, infrared (IR), gel permeation chromatography (GPC), elemental, and molecular weight, conducted on the polymeric products, indicated that phthalimide ring opening was occurring and that complex mixtures of poly(N-vinyl phthalimide) derivatives were formed. Both initiation methods gave comparable results, which further indicated mechanistic similarity between photo-and electroinitiation in these donor–acceptor charge transfer polymerizations. 相似文献
59.
Non-linear dielectric spectroscopy: antifouling and stabilisation of electrodes by a polymer coating
Woodward AM Davies EA Denyer S Olliff C Kell DB 《Bioelectrochemistry (Amsterdam, Netherlands)》2000,51(1):13-20
Non-linear dielectric spectroscopy (NLDS) has previously been shown to produce quantitative information that is indicative of the metabolic state of various organisms, by modeling the non-linear effects of their membranous enzymes on an applied oscillating electromagnetic field using supervised multivariate analysis methods. However, the instability of the characteristics of the measuring apparatus rendered the process temperamental at best in the laboratory and impractical for field use. The main practical problem, of the non-stationarity of the electrode-solution interface and the ease with which the electrode surfaces are subject to protein fouling. It is addressed by applying a thin, electrically transparent antifouling coat to the electrodes. This reduces the interminable cleaning procedures previously required to prepare the electrodes for use, increases their usable lifetime before recleaning, and also improves the precision and linearity of multivariate models on NLDS data. 相似文献
60.
A. N. Veselkov L. N. Dymant P. A. Bolotin S. F. Baranovskii D. Shipp D. Davies 《Journal of Structural Chemistry》1996,37(1):65-75
Complexation of the ethidium bromide (3,8-diamino-6-phenyl-5-ethylphenanthridine) dye with self-complementary deoxytetraribonucleoside
triphosphate 5′-d(CpGpCpG) in a water-salt solution is studied by one- and two-dimensional1H NMR spectroscopy (500 MHz). Two-dimensional PMR spectroscopy (2D-COSY and 2D-NOESY) is used for the full assignment of proton
signals of the molecules in the solution and for the qualitative analysis of the interaction between ethidium bromide and
the tetranucleotide. The concentration dependences of the proton chemical shifts of the molecules at a fixed temperature (T=308
K) are measured. Different schemes of the formation of the dye complexes with the tetranucleotide, taking into account various
molecular associations in the solution are considered. The equilibrium constants of the reactions and the limiting chemical
shifts of ethidium bromide protons in the complexes are determined. The relative contents of different complexes in the solution
are analyzed, and the dynamic equilibrium is studied as a function of the dye-tetranucleotide ratio in the solution. The data
obtained suggest that ethidium bromide (like the acridine dye proflavine) is intercalated predominantly into the pyrimidine-purine
sections (CG sites) of the tetranucleotide duplex. However, ethidium bromide is intercalated on the side of the narrow slot
of the duplex, while proflavine intercalation occurs through the broad slot of the double helix. The most likely structures
of the 1∶2 and 2∶2 dye-tetranucleotide complexes in the solution are constructed using the calculated values of the induced
chemical shifts of ethidium bromide protons and 2D NOESY spectroscopy data.
Sevastopol State Technical University. Berkbeck College, London University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 75–87, January–February, 1996.
Translated by I. Izvekova 相似文献