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91.
Internally consistent assignments of the 31P-{1H} NMR parameters of the complexes [Pt(RCCR′)(PPh3)2] are proposed, based on the premise that the magnitude of 1J(PtP) depends mainly on the nature of the moiety CR trans to P. For a given R, 2J(PP) correlates with 1J(PtP) for thebond trans to CR. The alkynes PhCCSnEt3, PhCCSnPh3, Me3SiCCCl, Me3SiCCBr, Et3SiCCI and MeCCI undergo oxidative addition reactions with [Pt(C2H4)(PPh3)2]; the intermediate alkyne complex was detected for PhCCSnEt3, Me3SiCCCl and Me3CCBr. The triyne Me(CC)3Me forms platinum(0) complexes by coordination with the central or terminal CC bond and appears also to give a platinum(II) complex by oxidative addition. 相似文献
92.
Gregory M. Shutske 《Journal of heterocyclic chemistry》1981,18(5):1017-1023
The synthesis of some novel anhydro-3-mercapto-5-pyrazinyl-1,2,4-triazolium hydroxides 5 is described. The appropriate 1-methylhydrazides 3 were condensed with isothiocyanates to give the thiosemicarbazides 4 which were cyclized to 5 under mildly basic conditions. A few 1,2,4-triazole-3-thiones 8 were synthesized for comparison, starting with the 2-methylhydrazides 6 and then carrying out analogous synthetic transformations. 相似文献
93.
Michielin O Zoete V Gierasch TM Eckstein J Napper A Verdine G Karplus M 《Journal of the American Chemical Society》2002,124(37):11131-11141
A conformational analysis of a stereochemically complete set of peptide analogues based on a cis-enediol unit is presented. The cis-enediol unit, which can replace a two or a three amino acid segment of a peptide, contains two "side chains", four asymmetrical carbon atoms, and six free dihedral angles. To determine the accessible conformational space, the molecules are divided into three fragments, each containing two free dihedral angles. The energy surfaces are computed for all dihedral angle values, and the possible conformations of the cis-enediol unit analogues are built using all combinations of the surface minima. Such a "build-up" procedure, which is very fast, is able to reproduce 75% of the minima obtained from a full dihedral angle exploration of the conformational space. The cis-enediol unit minima are compared with the corresponding di- and tripeptide minima; all peptide minima can be closely matched by a cis-enediol unit minimum of low energy (less than 2.2 kcal/mol above the lowest energy conformer). However, there are low energy minima of the cis-enediol unit that have no corresponding minima in peptides. The results are shown to depend strongly on the chirality of the analogues. The ability of each of the stereoisomers to mimic natural peptides, evaluated by the present approach, is correlated with its experimental activity in a renin inhibition assay. 相似文献
94.
ANTIVIRAL ACTIVITY OF MEROCYANINE 540 总被引:1,自引:0,他引:1
Fritz Sieber Jill M. O'Brien Gregory J. Krueger Sheri L. Schober William H. Burns Saul J. Sharkis Lyle L. Sensenbrenner 《Photochemistry and photobiology》1987,46(5):707-711
Abstract Simultaneous exposure to the lipophilic dye merocyanine 540 (MC 540) and white light inactivates several enveloped viruses. The same treatment appears to have little or no effect on pluripotent hematopoietic stem cells, mature red cells, and mature leukocytes. At least some components of the clotting system are spared, too. The molecular basis of the virucidal effect of MC 540 and light is not yet completely understood. Based on what is known about the interactions of MC 540 with cells and artificial membranes, it seems likely that MC 540 binds to and damages the viral envelope. MC 540-mediated photosensitization may have implications for the sterilization of bone marrow and blood products, the preparation of vaccines, and selected areas of antiviral therapy. 相似文献
95.
We report on the catalytic effects by alkali-metal ions in the ethanolysis of p-nitrophenyl diphenyl phosphate, in continuation of our studies on alkali-metal ion catalysis and inhibition in nucleophilic displacement reactions at carbon, phosphorus and sulfur centres. The following selectivity order of catalytic reactivity was observed for nucleophilic displacement at the phosphorus center with p-nitrophenoxide as leaving group: Li+ > Na+ > K+ > Cs+. A minor reaction pathway with phenoxide leaving was also found. The kobs data have been dissected into reaction pathways by free ions (kEtO) and by ion pairs (kMOEt), with the latter being dominant, in a 4-membered transition-state. Further analysis is given in terms of initial-state and transition-state stabilization by the alkali-metal ions in terms of the Eisenman model (electrostatic interaction vs. desolvation). Results of ab-initio MO calculations are presented based on interaction between M+ and a model bipyramidal phosphorane intermediate and compared with the sulfurane analogue. 相似文献
96.
97.
A synthesis and stereochemistry confirmation of a constituent recently isolated from the whole plant Isodon excisus is reported. An enantioselective catalytic boron-mediated reduction of an α-bromoketone was utilized in the key synthetic transformation. The methodology described herein was also used for the synthesis of the natural product's enantiomer and several derivatives. In addition, the compounds were evaluated for inhibitory activity in a caspase induction assay. The natural product was found to be devoid of activity, but several derivatives had moderate inhibitory activity (EC50<1 μM). 相似文献
98.
Keri T. Horne Gregory L. Powell Lee M. Daniels 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(5):m302-m303
The title complex [systematic name: pentachloro‐1κ3Cl,2κ2Cl‐tris(diethylphenylphosphino)‐1κP,2κ2P‐dirhenium(II,III)(Re—Re)], 1,3,6‐Re2Cl5(PEt2Ph)3 or [Re2Cl5(C10H15P)3], consists of dirhenium molecules with eclipsed structures similar to those of previously characterized 1,3,6‐Re2Cl5(PR3)3 compounds. The Re—Re bond distance is 2.2262 (3) Å and the metal–metal bond order is 3.5. 相似文献
99.
Boñaga LV Zhang HC Moretto AF Ye H Gauthier DA Li J Leo GC Maryanoff BE 《Journal of the American Chemical Society》2005,127(10):3473-3485
We investigated the formation of macrocycles from alpha,omega-diynes in cobalt-mediated co-cyclotrimerization reactions. Long-chain alpha,omega-diynes underwent metal-mediated [2 + 2 + 2] cycloadditions with nitriles, cyanamides, or isocyanates in the presence of CpCo(CO)2 (Cp = cyclopentadienide) to yield pyridine-containing macrocycles, i.e., meta- and para-pyridinophanes, such as 5m/5p, 35m/35p, and 41m/41p. The regioselectivity of these reactions was affected by the length and type of linker unit between the alkyne groups, as well as by certain stereoelectronic factors. An analogous alpha,omega-cyano-alkyne, 28, combined with an alkyne to yield two isomeric meta-pyridinophanes, such as 5m and 29m, and an ortho cycloadduct (benzannulation product), such as 29o. We developed a reaction protocol for these cobalt-based [2 + 2 + 2] cycloadditions that involves markedly improved conditions such that this process offers a convenient, flexible synthetic approach to macrocyclic pyridine-containing compounds. For example, diyne 6 reacted with p-tolunitrile in 1,4-dioxane to give 7p and 7m (7:1 ratio) in 87% yield at a moderate temperature of ca. 100 degrees C in 24 h without photoirradiation or syringe-pump addition. Isocyanates were also effective reactants, as exemplified by the formation of 44p almost exclusively (44p:44m > 50:1) in 64% yield from diyne 8 and 2-phenylethylisocyanate. By using this improved protocol we were able to co-cyclotrimerize long-chain alpha,omega-diynes with alkynes in certain cases to demonstrate a successful macrocyclic variant of the Vollhardt reaction. For instance, diyne 6 reacted with dipropylacetylene to give paracyclophane 57p and benzannulene 57o (2:1 ratio) in 29% yield. 相似文献
100.
Digrazia Philip M. Blackburn James W. Bienkowski Paul R. Hilton Barry Reed Gregory D. King J. M. Henry Sayler Gary S. 《Applied biochemistry and biotechnology》1990,(1):237-252
An experimental and mathematical method is developed for the microbial systems analysis of polyaromatic hydrocarbon (PAH)-degrading
mixed cultures in PAH-contaminated “town gas” soil systems. Frequency response is the primary experimental and data analysis
tool used to probe the structure of these complicated systems. The objective is to provide a fundamental protocol for evaluating
the performance of specific mixed microbial cultures on specific soil systems by elucidating the salient system variables
and their interactions. Two well-described reactor systems, a constant volume stirred tank reactor (CSTR) and a plug flow
differential volume reactor, are used in order to remove performance effects that are related to reactor type as opposed to
system structure. These two reactor systems are well-defined systems that can be described mathematically and represent the
two extremes of one potentially important system variable, macroscopic mass transfer. The experimental and mathematical structure
of the protocol is described, experimental data is presented, and data analysis is demonstrated for the stripping, sorption,
and biodegradation of napththalene. 相似文献