Is there a carboxylic group in the sodium channel of excitable biomembranes?

A model describing the effects of H⁺, Ca²⁺ and Cd²⁺ ions on the sodium channels of excitable membranes was developed. On the basis of this model, it was shown that the decrease in the amplitude of the sodium current in the membrane of the neurones of the mollusc Helix pomatia caused by extracellular Cd²⁺, Ca²⁺ and H⁺ ions is related to the change in the near-membrane concentration of sodium ions due to a decrease of the outer surface membrane potential. The data obtained allow us to suggest that the sodium channel, contrary to the calcium channel, does not contain the carboxylic group in its selectivity filter.     

Diels–Alder adducts of medium-ring carbocyclic dienes prepared by rearrangement of catalytically generated cyclic oxonium ylides

The novel bicyclic and tricyclic systems di­methyl (4aS*,6S*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexa­hydro-2H-benzo­cyclo­hept­ene-3,4-di­carboxyl­ate, C₁₆H₂₀O₆, (I), di­methyl (4aS*,6R*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexa­hydro-2H-benzo­cyclo­hept­ene-3,4-di­carboxyl­ate, C₁₆H₂₀O₆, (II), (3aS*,9R*,10aS*,10bR*)-9-methoxy-2-oxa-1,3a,4,6,7,8,9,10,10a,10b-deca­hydro-3H-cyclo­hepta­[e]­indene-1,3,8-trione, C₁₄H₁₆O₅, (III), and (1S*,2R*,9S*,10aR*)-9-methoxy-8-oxo-1,2,3,5,6,7,8,9,10,10a-deca­hydrobenzo­cyclo­octene-1,2-di­carboxyl­ic acid, C₁₅H₂₀O₆, (IV), have been crystallographically characterized, allowing the determination of the relative configuration of the stereogenic centres. The poor quality of the di­carboxyl­ic acid crystals necessitated the use of synchrotron radiation.     

Generation of sulfur ylides by the desilylation of α-trimethylsilylbenzyl sulfonium salts

The [2,3]-sigmatropic rearrangement of sulfur ylides derived via the desilylation of several α-trimethylsilylbenzyl sulfonium salts has been studied. The initially formed ylide was found to rapidly equilibrate with the thermodynamically more stable ylide. In the absence of trapping reagents, a Sommelet-Hauser type rearrangement occurs.     

Arylation of α-phosphoryl sulfides via their pummerer rearrangement intermediates generated from the corresponding sulfoxides

Various aryl groups were introduced directly into the α-position of α-phosphoryl sulfides by treating their sulfoxides with trifluoroacetic anhydride and then with tin (IV) chloride in the presence of excess of the aryl compound.     

The chemistry of photolytically and thermally generated α-ketocarbenes from iodonium ylides of β-diketones

The reactions of Phenyliodonium dimedonate,1,with various double bonds were investigated. The products are always heterocyclic copmounds(5-member ring) in good yield.     

Unexpected phenyl group rearrangement of Thiele’s hydrocarbon derivative under polycyclic aromatic hydrocarbon synthesis

An unexpected ketone was obtained in the synthesis of tetrabenzo[a,d,j,m]coronene having tert-butyl groups from Thiele’s hydrocarbon derivative. The structure of the product was confirmed by not only spectroscopic but also diffraction studies. This product was formed by the rearrangement reaction of one phenyl group and this reaction could be analogous to the pinacol-pinacolone rearrangement.     

One-pot synthesis of trans-β-lactams from ferrocenylketene generated by thermal Wolff rearrangement

A series of β-lactams containing the ferrocene moiety were synthesized through the Staudinger reaction between ferrocenylketene generated by the thermal Wolff rearrangement of the corresponding diazo ketone and various imines. The stereochemical outcome has been investigated and the trans-products were isolated as the main products, opposite to the reported results by Bonini and coworkers. The absolute configuration of (±)-trans-1,4-diphenyl-3-ferrocenylazetidin-2-one (3c) was determined by X-ray analysis. The stereoselectivity is discussed from the viewpoint of the reaction mechanism.     

Is the Beckmann rearrangement a concerted or stepwise reaction? A computational study

[reaction: see text] RB3LYP calculations were performed on the Beckman rearrangement by the use of three substrates, acetone oxime (1), acetophenone oxime (2), and cyclohexanone oxime (3). Acidic solvents were modeled by H+ (CH3COOH)3 and H3O+ (H2O)6, and reaction paths were determined precisely. For 1, a two-step process involving a sigma-type cationic complex was obtained. For 2, a three-step process with pi- and sigma-type complexes was found in H+ (CH3COOH)3 and a two-step process involving a sigma-type cationic complex was obtained in H3O+ (H2O)6. However, for 3, a concerted process without pi and sigma complexes was calculated, which leads to the product, epsilon-caprolactam. Three different mechanisms were explained in terms of FMO theory.     

Is the isonicotinoyl radical generated during activation of isoniazid by MnIII-pyrophosphate?

The antituberculosis drug isoniazid (INH) is quickly oxidised by stoichiometric amounts of manganese(III)-pyrophosphate and the following products were identified: isonicotinic acid 1, isonicotinamide 2 and isonicotinaldehyde 3, the acid being the major product. The oxidation of INH with Mn^III-pyrophosphate was carried out in either H₂¹⁶O, or H₂¹⁸O or D₂O and under varied atmosphere composition (argon, air, O₂ or ¹⁸O₂). LC–MS analyses of isotope incorporation suggest the simultaneous presence of two competitive pathways leading to the formation of acid 1, with the isonicotinoyl radical as a common intermediate. One route is oxygen-dependent and the other is water-dependent. Analyses of isotope incorporation in amide 2 and aldehyde 3 also support this mechanism.     

Is the ether group hydrophilic or hydrophobic?

A series of six surfactants, each with two ether oxygens within otherwise all-hydrocarbon chains, were synthesized and examined for their colloidal properties. Since an ether oxygen is sterically and conformationally similar to the methylene group it has replaced, the ether effect on micellization should stem mainly from solvation of the oxygen and, possibly, disrupted hydrophobicity of its adjacent carbons. It was found that critical aggregation values among the surfactants differ only modestly despite the total length of the ether-separated carbon segments ranging from 12 to 18. Shorter ether surfactants with only 12 or 14 total carbons appear to form small, loose aggregates owing, presumably, to a mild hydrophilicity of the ether groups. A surfactant with 18 chain carbons has a greater tendency to associate hydrophobically, but this is counterbalanced by a relatively water-free environment encountered by the ether groups within a more conventional micelle interior. The result is a leveling effect in which the critical aggregation concentration (cac) loses it sensitivity to chain length. Above their cac's, none of the ether surfactants is a good solubilizer of tetramethysilane or mesitylene. This is not necessarily a predictable finding since it was conceivable that the presence of interior ether groups might actually enhance solubilization (much as ether is a better solvent than hexane). Foamability and solid adsorption studies also indicate that the ethers impair surface activity. In response to the question posed in the paper's title, two ether groups are not sufficiently hydrophilic to prevent aggregation, but they do manage to alter the micelles' morphology and properties considerably.     

BINOL-derived phosphoramidites in asymmetric hydrogenation: can the presence of a functionality in the amino group influence the catalytic outcome?

In discovering the remarkable catalytic properties of BINOL-derived phosphoramidites (binoP-NR(2)), Dutch researchers recently achieved a long-awaited breakthrough in asymmetric catalysis. For the first time, easily accessible monodentate chiral P(III) ligands turned out to provide high enantioselectivities when used in rhodium-catalysed olefin hydrogenation. The simplest ligand representative of this family is MonoPhos, which can be made straightforwardly from BINOL and hexamethylphosphorous triamide. Since the first publication dealing with such catalysts (J. Am. Chem. Soc., 2000), a variety of binoP-NRR' ligands have been reported in which the amino group bears a functional substituent or a stereogenic centre. This critical review examines the impact of the presence of such a functionality in the amino group on catalytic olefin hydrogenation reactions.     

Is a major breakthrough in the oxygen electrocatalysis possible?

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Application of the taraxerane–oleanane rearrangement to the synthesis of seco-oleanane triterpenoids from taraxerone

Synthetic oleananes and seco-oleananes form a group of promising anti-inflammatory and cancer chemopreventive agents with an excellent safety profile. These compounds are usually prepared by semi-synthesis from natural oleanane triterpenoids. Since a taraxer-14-ene was reported to be rearranged into an olean-12-ene under mild reaction conditions, a rapid synthesis of seco-oleananes from taraxerone, which is a readily available starting material, was explored by us. Treatment of taraxerone with m-chloroperoxybenzoic acid gave 14,15-epoxy lactones, which underwent the taraxerane–oleanane rearrangement leading to new seco-oleanane triterpenoids.     

Intramolecular trapping of a cyclopropylidenamine during the favorskii rearrangement of α-chloroketimines

Cyclopropylidenamines have been trapped for the first time in an intramolecular way during the Favorskii rearrangement of suitably functionalized α-chloroketimines.     

Is there any group additive rules in the calculation of electron correlation energies of long straight chain alkane molecules?

According to the definition in the text, the correlation energy of 1s2C of carbon atoms, the primary and secondary C-H bonding electron pairs in some CH3, CH2 fragments and CH3(CH2)mCH3 (m=1-5) linear alkane molecules are calculated and analyzed. The transferability of the correlation energies of these electron pairs in the linear alkanes is investigated. The results indicate that the correlation energy of 1s2C is perfectly transferable in the respective methyl and methylene groups, while the correlation energies of the primary and secondary C-H bonding electron pairs are approximately transferable in methyl and methylene groups. The analysis of the results of group correlation energy shows that both of the correlation energies of methyl and methylene groups are transferable in these linear alkanes. The correlation energies of methylene group in CH3(CH2)mCH3 (m=1-5) molecules are slightly decreasing showing a converging trend to a "standard" methylene group in linear alkanes. The excellent fitting relationship between the total correlation energy and the number of methylene groups of the linear alkanes shows that the total correlation energy is a linear function of the number of methylene groups, which means that the total correlation energies of large linear alkanes can be reproduced and predicted by counting the numbers of methylene groups. In this way, total correlation energy of large linear alkane molecule can be approximately calculated using this simple group additive scheme with substantial saving in computational time.     

Is it possible to estimate the enantioselectivity of a chiral catalyst from its racemic mixture?

The evaluation of a racemic catalyst was investigated in the case of oxazaborolidine (OAB)-catalyzed borane reduction of 1,5-diphenyl-1,5-pentanedione, giving the corresponding diol. On the basis of the diastereoselectivity of the diols, it is possible to estimate the enantioselectivity (ee) of the first step, which correlates well with the ee in the reaction of the structurally similar phenyl n-pentyl ketone with enantiopure OAB catalyst. The measure of diastereoselectivity could be a tool for screening racemic catalysts without the need for resolving the individual enantiomers, if in the second step of the process there is no substrate control and no catalyst scrambling.     

What makes for a good catalytic cycle? A theoretical study of the SPhos ligand in the Suzuki-Miyaura reaction

The Suzuki-Miyaura cross-coupling reaction with the SPhos ligand was studied with DFT and analyzed within the energetic span model. With this information, we designed a modification to the SPhos (the "InPhos"), which theoretically corrects the deficiencies of the prior ligand.