Sulfur dioxide mediated one-pot, three- and four-component syntheses of polyfunctional sulfonamides and sulfonic esters: study of the stereoselectivity of the ene reaction of sulfur dioxide

The ene reaction of sulfur dioxide with enoxysilanes or with allylsilanes generates silyl sulfinates that can be brominated (Br(2) or NBS) or chlorinated (NCS or Cl(2)) to produce the corresponding sulfonyl halides. They react with primary and secondary amines or alcohols to give the corresponding sulfonamides and sulfonic esters, respectively. The hetero-Diels-Alder addition of sulfur dioxide to 1-oxy- or 1,3-dioxy-1,3-dienes generates zwitterions that add to enoxysilanes or allylsilanes giving silyl sulfinates that can be converted in situ into polyfunctional sulfonamides or sulfonic esters. This realizes quick access to libraries of complicated sulfonamides and sulfonic esters applying one-pot, three- and four-component methods.     

Alkenyl copper reagents—26 : Carbocupration of alkynes by organocopper reagents bearing a protected hydroxy or thiol function

Halohydrins, protected as ethers, acetals or chloro-magnesium alcoholates are sequentially transformed into the Li or Mg reagents and then into copper or cuprate derivatives. Addition to acetylene or propyne is discussed according to various parameters. The alkenyl copper or cuprate species, thus obtained, may react further with various electrophiles, leading to difunctionalized alkenes.     

The synthesis of naphthothiopyranopyranones and naphthothiopyranopyranthiones

The synthesis of fused tetracyclic naphthothiopyranopyranones from dihydronaphthothiopyranones I or II has been studied. Compounds I or II have been cyclised in good yield to the corresponding dioxaborin difluoride complexes III, IV, XIII and XIV by treatment with acetic or propionic anhydride and boron trifluoride etherate. These complexes and the Vilsmeier reagent reacted to produce fused tetracyclic 3-substituted naphthothiopyranopyranones V, VI, XV or XVI . The reaction of dioxaborin difluoride complexes III or IV with dimethylthioformamide (DMTF) afforded dimethylaminovinyldioxaborin difluoride complexes IX or X . Treatment of IX or X with hydrochloric acid solution gave naphthothiopyranopyranones VII or VIII . The reaction of VII, VIII, XV or XVI with DMTF/acetic anhydride yielded new products, which was identified as naphthothiopyranopyranthions XI, XII, XVII or XVIII .     

Cage‐to‐Cage Cascade Transformations

A series of Pd₂ L ₄‐type binuclear self‐assembled coordination cages ( 1 – 4 ), where L stands for a nonchelating bidentate ligand, were prepared. The strategies adopted for the synthesis of the cages were: combination of Pd^II with 1) a selected ligand or 2) subcomponents of the ligand. Highly efficient cage‐to‐cage transformation reactions are demonstrated by suitable covalent modification (from 1 to 2 or 3 or 4 ) or ligand‐exchange reactions (from 1 to 2 or 3 or 4 ; from 2 to 3 or 4 ). Thus, new cascade transformations (from 1 to 2 to 3 ; from 1 to 2 to 4 ) are achieved beautifully.     

Synthesis and application of inorganic/organic composite materials

A new type of inorganic-organic composite has been developed using organic monomeric or polymerizable silanes (with appropriate organic groupings like double bonds or epoxides) as monomers or in situ prepared or separately added nano-scale ceramic or metal particles. Due to the small size of the particulate phase, these composites are still highly transparent but show properties at least partially to be attributed to the inorganic phase. The introduction of special functions into these materials has been used for the fabrication of interesting functions like non-linear optical properties, low surface free energy coatings, controlled release properties or special mechanical properties (scratch resistance).     

Synthesis and cytotoxicity of 9-(2-deoxy-2-alkyldithio-beta-D-arabinofuranosyl)purine nucleosides which are stable precursors to potential mechanistic probes of ribonucleotide reductases

A series of 2[prime or minute]-thionucleosides, as potential inhibitors of ribonucleotide reductases, has been synthesized. Treatment of the 3[prime or minute],5[prime or minute]-O-TPDS-2[prime or minute]-O-(trifluoromethanesulfonyl)adenosine with potassium thioacetate gave the arabino epimer of 2[prime or minute]-S-acetyl-2[prime or minute]-thioadenosine which was deacetylated to give 9-(3,5-O-TPDS-2-thio-[small beta]-d-arabinofuranosyl)adenine in high yield. Treatment of the latter with diethyl azodicarboxylate-C(3)H(7)SH-THF gave 2[prime or minute]-propyl disulfide which was desilylated to give 9-(2-deoxy-2-propyldithio-[small beta]-d-arabinofuranosyl)adenine. Subsequent tosylation (O5[prime or minute]) and displacement of the tosylate with pyrophosphate afforded the 5[prime or minute]-O-diphosphate in a stable form as propyl mixed-disulfide, which upon treatment with dithiothreitol releases 9-(2-thio-[small beta]-d-arabinofuranosyl)adenine 5[prime or minute]-diphosphate. The arabino 2[prime or minute]-mercapto group might interact with the crucial thiyl radical at cysteine 439 leading to the inhibition of ribonucleotide reductases via formation of a Cys439-2[prime or minute]-mercapto disulfide bridge. The 2,6-diamino-, 2-amino-6-chloro- and 2-amino-6-methoxypurine ribosides were also converted to the corresponding 2[prime or minute]-deoxy-2[prime or minute]-propyldithio-[small beta]-d-arabinofuranosyl nucleosides, which might serve as convenient precursors to the arabino epimer of 2[prime or minute]-thioguanosine. Analogously, 2[prime or minute]-deoxy-2[prime or minute]-propyldithioadenosine was prepared from 9-([small beta]-d-arabinofuranosyl)adenine. The nucleoside disulfides show modest cytotoxicity in a panel of human tumor cell lines.     

Organic-inorganic nanohybrids through the direct tailoring of semiconductor nanocrystals with conjugated polymers

Two main synthetic strategies are used to prepare conjugated oligomer- or polymer-nanocrystal nanohybrids. In the first strategy ligand exchange is invoked to either replace with a bifunctional ligand, which contains a second functional group for coupling with conjugated oligomers or polymers (COs or CPs), or exchange for the functionalized COs or CPs in a "grafting-onto" process. Alternatively, in the second strategy the nanocrystal (NC) is passivated with functional ligands from which COs or CPs are directly grown in the absence of ligand exchange. The well-defined interface between the COs or CPs and NCs facilitates an efficient charge-transfer between them.     

Effect of surfactants on the stability of thin liquid film flow on a rotating disk

The effect of surfactants on surface instabilities of thin liquid film flow on a rotating disk was studied at different flow rates Q (0.5相似文献   

Liquid crystalline block copolymers by sequential cationic or promoted cationic and free-radical polymerizations

The scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free-radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase-separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers.     

Preliminary Investigation on the Action Modes of an Oligosaccharide-Producing Multifunctional Amylase

The action modes of an oligosaccharide-producing multifunctional amylase (OPMA) were investigated using glucose and some oligosaccharides as its substrates. OPMA did not cause the hydrolysis of maltose or isomaltose, but it catalyzed the α-1,6-transglycosylation of maltose to produce isomaltose or did the self-condensation of isomaltose to form isomaltotetraose and 4-O-α-isomaltosyl isomaltose. OPMA exhibited strong α-1,6-transglycosylation activity in addition to its α-1,4-hydrolytic activity on higher oligosaccharides substrates rather than bisaccharides. OPMA displayed high acceptor specificity in its transglycosylation or condensation reaction. OPMA seemed to only take glucose or isomaltose as the acceptor molecule in its transglycosylation or condensation reaction, which made glucose or isomaltose form higher products, and as a result, glucose or isomaltose were absent in the final products. In view of the simultaneously formation of several transglycosylation or condensation products, it was predicted that there might be separate donor and acceptor sites in OPMA’s active center and the fact that the catalytically active form of this enzyme included its homodimer or homotrimer supported this prediction. Accordingly, a special pathway, isomaltose pathway, for OPMA catalysis was proposed to emphasize the central or important signification of isomaltose in OPMA catalysis.     

Complex vesicle-based structures

Making nanotechnology practical is a challenge for modern research. Self-assembly is clearly going to be a necessary tool to realize practical and economic nanoscale structures. A biomimetic approach to the self-assembly of nanostructures will probably involve bilayer membrane vesicles as either the nanostructures themselves, or as templates or building blocks for more complex structures. Whether the vesicles are composed of surfactants, lipids or polymers, their stability in various environments must be optimized to suit the particular task at hand. Stabilizing the vesicles by polymerizing the surfactants themselves, or monomers templated within the vesicle or bilayer, has had a new surge of interest. Plating the vesicles, either by colloids or by polyelectrolytes, or templating the growth of various inorganic phases, has also shown promise, both in stabilizing the vesicle structure and in creating novel structures.     

Studies on the regio- and stereoselectivity of halohydroxylation of 1,2-allenyl sulfides or selenides

It was observed that the halohydroxylation of 1,2-allenyl sulfides or selenides with Br2 (CuBr2 or NBS) or I2 and water demonstrated a fairly good regioselectivity (i.e., the C=C bond that is remote from the S or Se atom was halohydroxylated with the halogen atom connecting to the middle carbon atom and the hydroxyl group connecting to the non-S terminal carbon or Se-substituted terminal carbon atom of the allene moiety), leading to the synthesis of synthetically important 3-organosulfur or seleno-2-haloallylic alcohols. The stereoselectivity depends on the nature of X+ and S or Se, showing a Z-selectivity with the matched Lewis acid-base pair.     

A method,based on statistical moments,to evaluate the kinetic parameters involved in unstable enzyme systems

The evaluation of individual rate constants involved in any reaction mechanism of an enzymatic systems first requires experimental monitoring of the time course of the concentration or product rate creation or of any enzyme species. The experimental progress curves obtained must then be fitted to the corresponding theoretical symbolic equation. Nevertheless, in some cases, e.g. when the equation involves two or more exponential terms, this fit is not easy and sometimes impossible. Simplification of the equation is usually required by assuming, for example, that the system has reached the steady-state, assuming an initial steady-state of a segment in the scheme of the reaction mechanism or assuming rapid equilibrium in one or more of the reversible steps, if there are any. But, obviously, simplified equations produce either fewer individual rate constants or global constants consisting of algebraic associations of individual rate constants or individual rate constants or global constants that might considerably differ from the real ones due to the approaches made. In this contribution, we suggest an alternative procedure for evaluating the rate constants of enzyme reactions corresponding to enzyme systems where one or more of the species involved is unstable or where one or more of the enzyme species is irreversibly inhibited, or both. The procedure is based on the numerical determination of statistical moments from experimental time progress curves. The fitting of these experimentally obtained moments to the corresponding theoretical expressions allows us, in most cases, to evaluate of all of the rate constants involved, with only a small error. To verify the goodness of the suggested procedure, it was applied to an unstable enzyme system which had previously been analysed with other methods. Finally, it is indicated how this procedure could also be extrapolated for application to any stable or unstable enzyme system.     

Explanation of Ionic Sequences in Various Phenomena. IV. General Method for Determination of the Type of Bonding in Polymers; Bonds in Ovalbumin,Ribonuclease, Collagen,Hemoglobin, and Starch Determined

Abstract

The salting-out or -in of hydrocarbons, uncharged nitrogen bases, and acids containing polarized hydroxyl groups give different cationic sequences. Also various ionic groups have different solubility sequences. Such neutral or electrostatically charged groups are attached to polymers and are involved as forces which hold together aggregates or helicies in inter- or intramolecular interactions. In aqueous solutions, the addition of various salts can destroy or produce these inter- or intramolecular interactions. Consequently, by applying the ionic solubility sequences, the observed salting-in and -out sequences of low molecular weight molecules, and other solubility criteria to the destruction or formation of such polymer interactions, it is possible to determine the major force or forces which are involved in holding the aggregate or helix together. Such forces involve hydrophobic bonds, hydrogen bonds between neutral bases, hydrogen bonds involving polarized hydroxyl groups, ionic bonds, and/or repulsive forces between electrostatically charged groups. The method is applied to the salting-out of ovalbumin, the destruction of the α-helix of ribonuclease, the collagen-gelatin transformation, the dissociation of hemoglobin, and the retrogradation and solubilization of starch. These five examples involve all the secondary forces considered. The method should find wide applicability because it can be applied to any method of physical measurement involving ionic solutions.     

Lewis acid-promoted deoxygenative di[beta,beta-bis(ethylthio)]vinylation of aldehydes with trimethylsilylketene bis(ethylthio)acetal

Silylketene dithioacetal 1 reacted with aldehydes 2a-o, 14, or cinnamaldehyde (11) in the presence of Lewis acid to give deoxygenative divinylation products, 3-substituted 1,4-pentadienes 3a-o, 15, or 5-phenyl-1,3,6-heptatriene 13b, in good to moderate yields. Similar reaction with 2-aminobenzaldehyde (16) or salicylaldehyde (17) produced quinoline 19 or chroman 20 in 40-58% yield. Treatment of 1 with alpha-diketones 22a-c or alpha-ketoester 24 led to tetrasubstituted furans 23a-c or allylic alcohol 25, respectively, in rather low yields. The formation mechanisms of these products are discussed.     

Electrokinetic Separation Methods

Electrophoresis is the transport of dissolved molecules or suspended particles in a homogeneous polar liquid (such as water) under the influence of an electric field. Most molecules or particles acquire a surface electric charge when dissolved or suspended in buffered water (or other polar liquids), owing to ionization or adsorption of ions present in the water. The sign of the surface charge of molecules or particles determines whether they will migrate towards the positive or the negative electrode of the applied electric field, and the velocity of migration depends on the surface potential of the molecules or particles, as well as on the potential of the electric field.     

Synthesis of 2'-deoxyadenosine nucleosides bearing bipyridine-type ligands and their Ru-complexes in position 8 through cross-coupling reactions

The synthesis of the title 2'-deoxyadenosine derivatives bearing bipyridine, phenanthroline or terpyridine ligands and their corresponding RuII-complexes in position 8 linked via acetylene or phenylene tethers was accomplished through cross-coupling reactions. The Suzuki-Miyaura reactions of boronic acids or the Sonogashira reactions of terminal acetylene derivatives of oligopyridine ligands were performed either on protected 8-bromoadenosines in organic solvents or, more efficiently, directly on unprotected nucleosides in aqueous acetonitrile or DMF. Direct cross-coupling reactions of unprotected nucleosides with RuII-complexes or the oligopyridine-boronic acids or -acetylenes gave the Ru-labelled nucleosides in one step in fair to good yields. This method was also proven to be applicable for direct Ru-labelling of dATP. Terpyridine-containing 2'-deoxyadenosine exerted significant antiviral and cytostatic effects.     

Infrared determination of calcium or lithium nitrate in acetone solution determination of calcium or lithium in the presence of strontium or barium

A method is proposed for the infrared determination of calcium or lithium in the presence of strontium or barium. A mixture of the nitrates is treated with acetone which dissolves only the calcium or lithium nitrate. The strontium or barium nitrate is filtered off. The nitrate is evaporated to about 2 ml with a stream of dry air and then diluted to 5 ml with acetone. The infrared spectrum is scanned from 860 to 800 cm(-1) and the nitrate peak at 824 cm(-1) for calcium and 827 cm(-1) for lithium is measured. The recommended range is 1-80 mg of calcium or lithium nitrate in the presence of up to about 200 mg of strontium or barium nitrate.     

An efficient reagent for synthesis of α,β-unsaturated aldehydes 3-methylthio-2-propenyl p-tolyl sulfone

Alkylation of 3-methylthio-2-propenyl p-tolyl sulfone (1) with an alkyl halide and a base (NaH or KOH-TOMAC) took place at the position α to the sulfonyl group to give optionally a mono- or dialkylated product (2 or 3), which was converted to β-monosubstituted or β,β-disubstituted α,β-unsaturated aldehyde (6 or 7), respectively, by TiCl₄-assisted hydrolysis followed by the removal of p-toluenesulfinic acid.     

Reaction of 3,4-disubstituted 1,2,5-oxadiazole 2-oxides with dipolarophiles : Substituent and solvent effect on the reaction courses

A variety of symmetrically or unsymmetrically 3,4-disubstituttd furoxans such as dicyano, dialkyl, diacyl, bis(phenylsulfonyl), N.N'-dialkyldicarbamoyl, 3(or 4)-methyl-4(or -3)-phenyl(or nitro, ethoxy, phenoxy, phenylthio, pyrrolidinyl, phenylsulfonyl), 3(or 4)-ethyl-4(or -3)phcnyl, and 3(or 4)-ethoxy-4(or -3)-phenylsulfonylruroxan reacted with dipolarophiles in toluene or xylene at the refluxing temperature to give nitrone-type 1,3-dipolar cycloadducts, 5-substituted 1-aza-2,8-dioxabicyclo-[3.3.0]octanes and/or 3-substituted 2-isoxazoline 2-oxides. On the other hand, some of the furoxans gave 2-isoxazolines via nitrile oxide 1,3-dipolar cycloaddition in a toluene (or xylene)-DMF solvent at the refluxing temperature.