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101.
Schmidt D Conrad J Klaiber I Beifuss U 《Chemical communications (Cambridge, England)》2006,(45):4732-4734
5-Hydroxy-3-oxopent-4-enoic acid esters can be efficiently transformed into the stable bis-potassium salts of the corresponding 5-hydroxy-3-oxopent-4-enoic acids, from which the sensitive acids are released in situ, the latter being converted into substituted 4-hydroxy-2H-pyran-2-ones, pyrazoles and isoxazoles under mild conditions; the efficiency of this method is demonstrated by the first synthesis of two naturally occurring pyrones. 相似文献
102.
Iron complexes of porphyrins (and corroles to a lesser extent) are the first catalysts to utilize ammonia for the synthesis of N-free amino acid esters. 相似文献
103.
104.
Rudzevich Y Rudzevich V Schollmeyer D Thondorf I Böhmer V 《Organic & biomolecular chemistry》2006,4(21):3938-3944
The crystal structure of the homodimer formed by the tritolylurea 3a proves the existence of a belt of six bifurcated hydrogen bonds between both NH and the O=C groups of the adjacent urea residues. For the tritosylurea 3b, four additional three-center hydrogen bonds, also involving the SO2 oxygen, are found in the crystalline state. Molecular dynamics simulations in a chloroform box confirm these patterns of the hydrogen bonds and the resulting elongation of the dimer 3b. 3b in comparison to 3a x 3a. The calculated complexation energies for the three dimeric combinations are nearly identical in agreement with the simultaneous formation of heterodimer 3a x 3b in a mixture of 3a and 3b. 相似文献
105.
T. Ranganathan Bon‐Cheol Ku Joseph Zilberman Michael Beaulieu Richard J. Farris E. Bryan Coughlin Todd Emrick 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4573-4580
Deoxybenzoin‐based copolymers containing various relative ratios of arylate and phosphonate units in the backbone were synthesized by solution polycondensation. These copolymers were characterized by gel permeation chromatography, Fourier Transform infrared spectrometry, and proton, carbon, and phosphorous nuclear magnetic resonance spectroscopy (1H, 13C, and 31P NMR). Pyrolysis combustion flow calorimetry (PCFC) performed on these copolymers revealed their very low heat release capacity, making them attractive for applications in which halogen‐free, low flammability materials are desired. Integration of phosphonate units into the polymer backbone is advantageous for achieving high molecular weight polymers with solution processbility while retaining the low flammability inherent to deoxybenzoin‐based polymers. Char yields greater than 50% and heat release capacities of 40–60 J/g K, were observed for these copolymers by PCFC. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4573–4580, 2007 相似文献
106.
The dithiol trypanothione can reduce an antiparasitic pentavalent antimony agent to trivalent rapidly; this reduction process is both pH and temperature dependent and trypanothione may therefore play an important role in the activation of the drug. 相似文献
107.
Oleg Kasyan Iris Thondorf Michael Bolte Vitaly Kalchenko Volker Bhmer 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(5):o289-o294
The structures of three syn‐1,3‐dialkoxythiacalix[4]arenes with unusual conformations in the solid state are reported. The pinched cone conformation of syn‐22,42‐dihydroxy‐12,32‐bis(prop‐2‐enyloxy)thiacalix[4]arene, C30H24O4S4, (3a), is stabilized by two intramolecular hydrogen bonds, remarkably formed from both OH groups to the same ether O atom. In syn‐22,42‐dihydroxy‐15,25,35,45‐tetranitro‐12,32‐bis(prop‐2‐enyloxy)thiacalix[4]arene acetone disolvate, C30H20N4O12S4·2C3H6O, (3b1), the molecule is found in the 1,3‐alternate conformation. The crystallographic C2 symmetry is due to a twofold rotation axis running through the centre of the calixarene ring. The hydroxy groups cannot form intramolecular hydrogen bonds as in (3a) and both are bonded to an acetone solvent molecule. The molecule of the pseudo‐polymorph of (3b1) in which the same compound crystallized without any solvent, viz. (3b2), is located on a crystallographic mirror plane. Only one of the two hydroxy groups forms a hydrogen bond, and this is with a nitro group of a neighbouring molecule as acceptor. Molecular mechanics calculations for syn‐1,3‐diethers suggest a preference of the 1,3‐alternate over the usual cone conformation for thiacalix[4]arene versus calix[4]arene and for para‐nitro versus para‐H derivatives. 相似文献
108.
The mechanical behaviors of polyether (ET) and polyester (ES) soft segment urethane-ureaelastomeric fibers constrained at different levels of elongation have been investigated by means ofdynamic mechanical tests and force-temperature measurements. The dynamjc mechanical re-sponse of the ET urethane-urea showed some difference from that of the ES as a function of exten-sion ratio. For force-temperature measuring the existence of a low temperature transition corre-sponding to the glass transition (T_(g's)) of the ester or ether soft segments, stress-softening tempera-ture (T_s) and initial melting temperature (T_(mh)) of hard segment crystallites was observed. The resultof cyclic testing of a constrained sample as a function of temperature indicated that the irreversibledecrease in stress implied a permanent change in sample microstructure. 相似文献
109.
A catalytic DNA-templated reaction of hydrolysis of an ester group in an N-modified peptide nucleic acid, which is activated by a Cu2+ complex-PNA, has been discovered and optimized. Both the ester-containing PNA and the metal complex PNA bind neighboring sites on a template DNA. This brings the reacting groups (the ester and the Cu2+ complex) in proximity to each other and accelerates the hydrolysis of the ester approximately 500 times in comparison with its hydrolysis in the absence of the template. The hydrolysis reaction provides >10(2)-fold kinetic discrimination between DNAs that are different from each other at a single nucleotide position. Natural enzyme T4 DNA ligase is slightly less selective. On the basis of this reaction a fully homogeneous and sensitive assay for sequence-specific DNA detection has been developed (10 fmol DNA). Identification of one of four DNAs (variation at one position) can be done in a single experiment. Since the Cu2+ ion is tightly bound in an associate containing the ester PNA, the metal complex PNA, and the template DNA, application of this method in buffers containing other Cu2+-binding ligands, e.g., PCR buffer and physiological buffer, is possible. 相似文献
110.
Miroslav Novakovic Iris Djordjevic Nina Todorovic Snezana Trifunovic Boban Andjelkovic Boris Mandic 《Natural product research》2019,33(19):2837-2844
New aurone epoxide, 2,10-oxy-10-methoxysulfuretin (14), and new auronolignan (15), named cotinignan A, were isolated by silica gel column and semipreparative HPLC chromatography from the methylene chloride/methanol extract of Cotinus coggygria Scop. heartwood. In addition, thirteen known secondary metabolites namely sulfuretin, 2,3-trans-fustin, fisetin, butin, butein, taxifolin, eriodictyol, 3',5,5',7–tetrahydroxyflavanone, 3',4',7-trihydroxyflavone, 3-O-methyl-2,3-trans-fustin, 3-O-galloyl-2,3-trans-fustin, β-resorcylic acid and 3-O-β-sitosterol glucoside were isolated as well. Their structures were elucidated by 1D and 2D NMR, HR-ESI-MS, IR and UV. Ten out of eleven isolated flavonoids possess 7, 3' and 4' hydroxy groups. These structural features could be considered as chemotaxonomic characteristic of flavonoids from C. coggygria. Cotinignan A (15) represents new subclass of secondary metabolites - auronolignans.