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81.
A synthesis of novel 3′-deoxy analogs of the anti-HBV agent entecavir (BMS-200475) was devised using regioselective ring opening of suitable cyclopentene epoxides as the key step. This versatile approach afforded access to an enantiomeric pair of carbocyclic nucleosides from a single chiral intermediate. 相似文献
82.
The infrared spectra of eighteen metal complexes of empirical formula [ML2X2] (M = Co, Ni, Cu or Zn; L = o? or m-toluidine; X = Cl, Br or I) have been determined over the range 4000-150 cm?1. Assignments of the internal vibrations of the amino group are based on the band shifts induced by 15N-labelling of the nitrogen donors. Bands within the range 400–600 cm?1 are assigned to the metal-nitrogen stretching frequency (vM-N) on the grounds of their sensitivity to 15N-labelling and metal ion substitution and their absence of sensitivity to halide substitution. Bands within the range 350–150 cm?1 are assigned to the metal-halogen stretching frequency (vM-X) on the basis of their sensitivity to halide and metal ion substitution and their insensitivity to 15N-labelling. Structural aspects of the spectra are discussed and the present assignments are compared with those previously reported. 相似文献
83.
Isolation and structure elucidation of a novel yellow pigment from the marine bacterium Pseudoalteromonas tunicata 总被引:3,自引:0,他引:3
Franks A Haywood P Holmström C Egan S Kjelleberg S Kumar N 《Molecules (Basel, Switzerland)》2005,10(10):1286-1291
The marine environment is a major source for many novel natural compounds. A new yellow pigment has been isolated from the marine bacterium P. tunicata and identified as a new member of the tambjamine class of compounds. The structural identification was achieved by a combination of 1D and 2D-NMR spectroscopy and high resolution mass spectrometry data. 相似文献
84.
Carola W. N. Damen Jurjen S. Lagas Hilde Rosing Jan H. M. Schellens Jos H. Beijnen 《Biomedical chromatography : BMC》2009,23(12):1316-1325
A sensitive, specific and efficient high‐performance liquid chromatography/tandem mass spectrometry assay for the simultaneous determination of vinorelbine and its metabolite 4‐O‐deacetylvinorelbine in human and mouse plasma is presented. Heated electrospray ionization was applied followed by tandem mass spectrometry. A 50 µL plasma aliquot was protein precipitated with acetonitrile–methanol (1:1, v/v) containing the internal standard vinorelbine‐d3 and 20 µL volumes were injected onto the HPLC system. Separation was achieved on a 50 × 2.1 mm i.d. Xbridge C18 column using isocratic elution with 1 mm ammonium acetate–ammonia buffer pH 10.5–acetonitrile–methanol (28:12:60, v/v/v) at a flow rate of 0.4 mL/min. The HPLC run time was 5 min. The assay quantifies both vinorelbine and 4‐O‐deacetylvinorelbine from 0.1 to 100 ng/mL using sample volumes of only 50 µL. Mouse plasma samples can be quantified using calibration curves prepared in human plasma. Validation results demonstrate that vinorelbine and 4‐O‐deacetylvinorelbine can be accurately and precisely quantified in human and mouse plasma with the presented method. The assay is now in use to support (pre‐)clinical pharmacologic studies with vinorelbine in humans and mice. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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88.
Barrera C Herrera AP Bezares N Fachini E Olayo-Valles R Hinestroza JP Rinaldi C 《Journal of colloid and interface science》2012,377(1):40-50
The size, charge, and stability of colloidal suspensions of magnetic nanoparticles with narrow size distribution and grafted with poly(ethylene glycol)-silane of different molecular weights were studied in water, biological buffers, and cell culture media. X-ray photoelectron spectroscopy provided information on the chemical nature of the nanoparticle surface, indicating the particle surfaces consisted of a mixture of amine groups and grafted polymer. The results indicate that the exposure of the amine groups on the surface decreased as the molecular weight of the polymer increased. The hydrodynamic diameters correlated with PEG graft molecular weight and were in agreement with a distributed density model for the thickness of a polymer shell end-grafted to a particle core. This indicates that the particles obtained consist of single iron oxide cores coated with a polymer brush. Particle surface charge and hydrodynamic diameter were measured as a function of pH, ionic strength, and in biological buffers and cell culture media. DLVO theory was used to analyze the particle stability considering electrostatic, magnetic, steric, and van der Waals interactions. Experimental results and colloidal stability theory indicated that stability changes from electrostatically mediated for a graft molecular weight of 750 g/mol to sterically mediated at molecular weights of 1000 g/mol and above. These results indicate that a graft molecular weight above 1000 g/mol is needed to produce particles that are stable in a wide range of pH and ionic strength, and in cell culture media. 相似文献
89.
Arup Mukherjee Tamal K. Sen Dr. Pradip Kr. Ghorai Dr. Prinson P. Samuel Dr. Carola Schulzke Dr. Swadhin K. Mandal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10530-10545
Herein, we report the synthesis and characterization of two organozinc complexes that contain symmetrical phenalenyl (PLY)‐based N,N‐ligands. The reactions of phenalenyl‐based ligands with ZnMe2 led to the formation of organozinc complexes [N(Me),N(Me)‐PLY]ZnMe ( 1 ) and [N(iPr),N(iPr)‐PLY]ZnMe ( 2 ) under the evolution of methane. Both complexes ( 1 and 2 ) were characterized by NMR spectroscopy and elemental analysis. The solid‐state structures of complexes 1 and 2 were determined by single‐crystal X‐ray crystallography. Complexes 1 and 2 were used as catalysts for the intramolecular hydroamination of unactivated primary and secondary aminoalkenes. A combined approach of NMR spectroscopy and DFT calculations was utilized to obtain better insight into the mechanistic features of the zinc‐catalyzed hydroamination reactions. The progress of the catalysis for primary and secondary aminoalkene substrates with catalyst 2 was investigated by detailed kinetic studies, including kinetic isotope effect measurements. These results suggested pseudo‐first‐order kinetics for both primary and secondary aminoalkene activation processes. Eyring and Arrhenius analyses for the cyclization of a model secondary aminoalkene substrate afforded ΔH≠=11.3 kcal mol?1, ΔS≠=?35.75 cal K?1 mol?1, and Ea=11.68 kcal mol?1. Complex 2 exhibited much‐higher catalytic activity than complex 1 under identical reaction conditions. The in situ NMR experiments supported the formation of a catalytically active zinc cation and the DFT calculations showed that more active catalyst 2 generated a more stable cation. The stability of the catalytically active zinc cation was further supported by an in situ recycling procedure, thereby confirming the retention of catalytic activity of compound 2 for successive catalytic cycles. The DFT calculations showed that the preferred pathway for the zinc‐catalyzed hydroamination reactions is alkene activation rather than the alternative amine‐activation pathway. A detailed investigation with DFT methods emphasized that the remarkably higher catalytic efficiency of catalyst 2 originated from its superior stability and the facile formation of its cation compared to that derived from catalyst 1 . 相似文献
90.
Bijan Nekoueishahraki Dipl.‐Chem. Sankaranarayana Pillai Sarish Dipl.‐Chem. Herbert W. Roesky Prof. Dr. Daniel Stern Carola Schulzke Prof. Dr. Dietmar Stalke Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(25):4517-4520
Bi? O chemistry : A direct regioselective route to bismuth bis(amino)naphthalene compounds, incorporating Bi? O and Bi? C bonds is described, in which an amide precursor is treated with aldehydes, ketones, alkenes, and alkynes, leading to insertion into the Bi? NMe2 bond.