Purine nucleosides XVII. The synthesis and conformation of 6-amino-9-β-D-ribopyranosylpurine and related derivatives prepared via the fusion procedure

The preparation of 2, 6-dichloro-9-(2′,3′,4′-tri-O-acetyl-β-D-ribopyranosyl)purine (I) has been accomplished utilizing the acid catalyzed fusion procedure. The displacement of the 6-chloro group, or the 2- and 6-chloro group has been studied. Several new 6-substituted-9-(β-D-ribopyranosyl)purines have been prepared by catalytic dehalogenation of the corresponding 2-chloropurine nucleosides. The conformation and configuration of these D-ribopyranosylpurines has been assigned with the assistance of proton magnetic resonance studies.     

Effect of chemical structure on the properties of some hydrogels prepared by using gamma radiation polymerization

Several hydrogels were prepared using radiolytic polymerization of aqueous solutions of acrylamide or acrylamide containing appropriate comonomer such as acrylic acid, maleic acid, itaconic acid, and maleic anhydride. The hydrogels have been prepared at an irradiation dose of 30 kGy. The effects of the chemical structure of the monomer(s) and crosslinking agents on the yield of homopolymer(s) or copolymers have been studied. These crosslinking agents include N, N′‐methylene dimethacrylate (MDA) and N, N′‐methylene bisallyamide (MBA). The hydrogels obtained were characterized using swelling technique, thermal and spectroscopic analysis. The results obtained showed that the prepared samples are able to reject sodium ions and are not able to recover the Basic Blue Dye from their aqueous solution. © 2005 John Wiley & Sons, Ltd.     

Synthesis of oligo(phenyleneethynylene)s containing central pyromellitdiimide or naphthalenediimide groups and bearing terminal isocyanide groups: molecular components for single-electron transistors

Oligo(phenyleneethynylene)s that are of variable length, contain a central arenediimide unit, either a pyromellitdiimide or a naphthalenediimide group, and are terminated by isocyanide groups have been prepared. The extended frameworks were assembled from appropriately functionalized arenediimide and areneformamide units whose lengths were adjusted by adding phenyleneethynylene units. Final transformation of the formamide groups into isocyanide groups gave the title compounds. Several isocyanide-terminated oligo(phenyleneethynylene)s without an arenediimide unit have also been prepared.     

The effect of additives on the polymerization of methyl methacrylate. tris(1,2-dibromo-propyl)phosphate

The effect of the additive, Tris(1,2-dibromopropyl)phosphate, on the kinetics of free radical polymerization of methyl methacrylate is studied. No marked differences were observed in the homopolymerization despite the reported effect of this additive on the mechanical properties of the resulting polymer. It was concluded that the additive was a multifunctional transfer agent producing linear and branched polymer molecules. Several model transfer agents have been studied to confirm these conclusions. H-NMR spectra of the polymer confirm that there is no change in the stereoregularity of the polymer prepared in the presence of this additive, and no copolymerization of the phosphate unit.     

Povarov reactions of exo-glycals: preparation of C-linked, quinoline analogues

A one-pot approach based upon the Povarov reaction has been efficiently employed with a number of exo-glycals and para-substituted benzanilines to synthesize novel open-ring, carbohydrate-derived quinolines. The mechanism of this reaction was studied and an explanation for the observed stereoselectivity is proposed. Treatment of the compounds with the Lewis acid, boron trichloride, successfully removes the benzyl ether protecting groups in good yields. Several of the prepared compounds have been screened in the National Cancer Institute’s (NCI’s) 60 cell line model. Moderate activity was observed for several leukemia cell lines.     

N-（2-甲基）苯基甘氨酸的三价和四价金属/非金属衍生物(英)

用N-（2-甲基）苯基甘氨酸合成了几种（硼、铝、铁、砷和锑）及四价（硅、钛和硒）金属/非金属衍生物。合成是在苯溶液中采用了金属/非金属的异丙氧基化合物和N-（2-甲基）苯基甘氨酸按1∶1和1∶2的配比完成的。一般情况下，合成的产物均为有色固体，以及在产物中有异丙氧基基团残留而显吸湿性。对所制成的衍生物均采用了共沸混合物分析、元素分析和光谱测定等进行了表征。     

Reversible and irreversible thermochromism of some Schiff base metal complexes

Summary Nickel(II) and copper(II) complexes of Schiff bases derived from salicylaldehyde, 2-hydroxy-1-naphthaldehyde, 2,4-dihydroxybenzaldehyde, 2,3-dihydroxybenzaldehyde or 5-chlorosalicylaldehyde and 8-aminoquinoline have been prepared and characterized. Several of the complexes are thermochromic in the solid state. The origin of the thermochrornism is discussed in terms of changes in ligand field strength and coordination geometry. These changes were studied by means of thermal and spectral methods.     

Dimesogenic compounds consisting of a cholesteryl moiety and an aromatic mesogen interconnected through a central pentamethylene spacer

New non-symmetric dimesogens consisting of a cholesteryl moiety and an aromatic mesogenic unit interconnected through a pentamethylene spacer have been prepared. The aromatic units consist of two phenyl rings linked by carboxy, oxycarbonyl, ethylene, ethynylene, azo or Schiff's base groups. The mesomorphic and transitional properties have been investigated by using optical microscopy, differential scanning calorimetry, helical pitch measurements, and electric field and miscibility studies. The structures of the mesophases have been studied using X-ray diffraction. Several kinds of smectic packings are observed depending on the nature of the linking group and an attempt to understand the origin of the different phase structures at a molecular level is made.     

Thermal degradation studies of methacrylonitrile polymers and copolymers—3. Polymers capable of chain end-initiated colouration

Polymethacrylonitrile (PMAN) prepared by free-radical polymerisation with the initiator 4,4′-azo-bis(4-cyanovaleric acid) (ACVA) has chain ends from the initiator fragment which incorporate carboxyl groups. These ends are found to act as reactive sites for initiation of colouration in the polymer at temperatures from 140 °C. Several polymers, with different chain-end concentrations, have been made and the thermal degradation behaviour has been studied under programmed heating in the absence of air to 500 °C, with full product characterisation. In contrast with pure PMAN prepared with 2,2′-azo-bis(isobutyronitrile) (AIBN) as initiator, which degrades quantitatively to monomer, these ACVA-initiated polymers give very much reduced monomer yields, an important tar/wax fraction and a substantial amount of residue, amounting to 32–48% of the sample weight, dependent on the initial molecular weight of the polymer. The infrared spectral changes at the onset of the colouration reaction have been examined at 160 °C. Mechanisms are suggested to account for the observed products.     

Studies on sulphur heterocycles. Reactions of 6,7-dihydrobenzo[b]thiophen-4(5H)one derivatives and their conversion to 7-substituted thieno[2,3-h][1]benzopyran-8-ones

Cyclization of γ-(2-thienyl)butryic acid with acid anhydrides gives 2-acyl derivatives as well as the expected 6,7-dihydrobenzo[b]thiophen-4(5H)one. Several reactions of these ketones have been studied including their conversion to 0,0-diethyl thiophosphonohydrazones. 7-Substituted thieno[2,3-h][1]benzopyran-8-ones have been prepared via 4-hydroxybenzo[b]thiophen-5-carbaldehydes.     

Synthesis and characterisation of bite angle-dependent (η1-allyl)Rh and (η3-allyl)Rh complexes bearing diphosphine ligands. Implications for nucleophilic substitution reactions

Several novel rhodium allyl complexes have been prepared and their structures have been studied using NMR spectroscopy and X-ray crystallography. Depending on the bite angle of the ligand and the substitution pattern of the allyl group, two different coordination modes (η¹ and η³) have been observed for the allyl moiety. The activities of these Rh allyl complexes in the allylic alkylation reaction have been tested. We have shown that both coordination modes give active complexes in this reaction, but that the regioselectivity is dependent on the coordination mode of the allyl group.     

First synthesis of S,S-dialkyl difluorophosphonodithioates and difluorophosphonotrithioates

Several dialkyl difluoromethylphosphonodithioates and difluoromethylphosphonotrithioates have been prepared from difluoromethylphosphonyl dichloride and two equivalents of alkanethiols under basic conditions. Treatment of these species with LDA at low temperatures mainly resulted in decomposition, and to the low-yield isolation of difluorophosphinates or phosphine oxides, thus reflecting the lability of the P-S bond. The desired difluorophosphonodithioates and difluorophosphonotrithioates can be efficiently prepared by reversing the sequence of reactions.     

Modification of fluorocopolymer coatings by telomers to improve their hydrophobicity

In this work, modification of coatings based on FP-5182 lacquer that is prepared from the copolymer of trifluorochloroethylene and vinylidenefluoride (F-32L) has been performed in order to improve their hydrophobicity. Several approaches to modification have been suggested, among which is the use of telomeric solutions of tetrafluoroethylene that were synthesized in various solvents, variation of the roughness of the coating surface by the aerosil powder, and a combination of these two approaches. The wetting properties of coatings have been studied, and improvement of the hydrophobic characteristics during their modification has been demonstrated.     

Enantioselective epoxidation of alkenes catalyzed by 2-fluoro-N-carbethoxytropinone and related tropinone derivatives

Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities.     

Co‐poly(aryl ether sulfone)s containing phthalimidine moiety in the main chain

Several new co‐poly(arylene ether sulfone)s have been prepared by the reaction of 4,4′‐fluorodiphenyl sulfone (FDS) with different bisphenols namely 4,4′‐isopropylidenediphenol (BPA), 4,4′‐hexafluoroisopropylidenediphenol (6F‐BPA), and N‐phenyl‐3,3‐bis(4‐hydroxyphenyl)phthalimidine(PA). The homo‐poly(arylene ether sulfone)s are named as 1a, 2a, and 3a. The copolymers namely 2b, 2c, 2d and 3b, 3c, 3d have been prepared, respectively, on reaction of FDS with BPA or 6F‐BPA using different molar ratios of PA such as 25, 50, and 75. The poly(aryl ether sulfone)s 1a containing PA unit in the main chain showed a very high glass transition temperature of 280°C and an outstanding thermal stability up to 510°C for 5% weight loss under synthetic air. Depending on the mole% of PA, the glass transition temperatures of the copolymers can be varied. The polymers were soluble in a wide range of organic solvents. Transparent thin films of these polymers exhibited tensile strengths upto 84 MPa and Young's modulus up to 3.16 GPa. The films of these polymers showed low water absorption of 0.24%. Copyright © 2009 John Wiley & Sons, Ltd.     

New polymer syntheses. LXI. Synthesis and alkylation of aromatic poly(pyrazine-ether)s

Three poly(pyrazine-ether)s were prepared from 2,6-dichloropyrazine, silylated bisphenol-A and, in two cases, 4,4′-dichlorodiphenylsulfone. The alkylation of these poly(pyrazine-ether) with methyl triflate, dimethyl sulfate, methyl 4-nitrobenzenesulfonate, or γ-propanesultone was studied by ¹H-NMR spectroscopy in nitrobenzene. Several N-methylated poly(pyrazine-ether)s were also isolated and characterized by elemental analyses, inherent viscosities, ¹H-NMR spectra, ¹⁵N-NMR spectra, and DSC measurements. Furthermore, their solubilities in six different solvents were determined. Complete methylation raises the glass transition temperatures, reduces the solubility in aprotic solvents, and favors dissolution in methanol or ethanol.     

高分子载钯催化剂对有机锡烷偶联反应的催化性能及结构表征

制备了几种负载型钯催化剂，用于有机锡烷与有机卤化物的偶联反应中，考察了催化剂的使用寿命及载体对催化剂催化活性的影响，通过XPS、XRD、电镜等技术对催化剂进行了表征。结果表明，催化活性中心的质点钯是金属态钯，即催化剂中的钯可以看成是两配位不饱和的，经过氧化加成、金属转换、还原消除过程完成催化反应。     

The formation of mixed copper(II) sulfide—silver(I) sulfide membranes for copper(II)-selective electrodes

Several methods for the preparation of mixed copper(II) sulfide—silver(I) sulfide precipitates have been investigated. Pellets of these materials have been tested for their suitability as copper(II)-selective membranes. Homogeneous membranes with satisfactory electrochemical properties can be prepared only from precipitates obtained by addition of the metal salts to sodium sulfide Membrane leakages, limits of detection, calibration curves and titration curves with different types of precipitate are discussed.     

Study on the feasibility of TLC/FID to reveal chemical composition distributions of copolymers obtained by emulsion processes

The CCD (chemical composition distribution) of poly(styrene-co-ethyl methacrylate) has been determined by thin layer chromatography/flame ionization detection (TLC/FID). It appeared that a mixture of five reference copolymers obtained by solution polymerization each having a narrow CCD, could be separated in five distinct peaks, provided a modified spotting procedure and a concentration gradient elution technique were applied. All copolymers prepared by solution polymerization could be successfully characterized. Copolymers obtained by emulsion techniques using nonionic or anionic surfactants containing oxyethylene groups, or in the absence of chain length modifier behaved anomalously and appeared to have spurious CCD's. Also the average composition calculated from these CCD's did not agree with the average composition determined by ¹H-NMR. This anomalous behaviour disappeared when using sodium lauryl sulfate as surfactant or when applying a chain length modifier (n-dodecyl mercaptan) during the preparation of the polymer. Several possibilities have been proposed in order to explain these phenomena. The most probable explanation seems to be reaction of a growing polymer chain with surfactant molecules resulting in a quasi-terpolymer. This polymer containing highly polar oxyethylene groups, remains strongly adsorbed on the silica surface during elution, thus disturbing the separation process.     

Preparation of crown compounds containing allyloxymethyl or butenyl groups for attachment to silica gel or containing long chain lipophilic groups for use in liquid membrane systems

Several new macrocyclic polyether ligands have been prepared for use in the separation of metal ions from aqueous solutions. Four of the crown ethers reported contain 1,2,4-triazole or 4-pyridone protonionizable subcyclic units and lipophilic groups. The remaining crown ethers are not proton-ionizable but contain alkene groups and were prepared for attachment to silica gel. The crowns were prepared by reacting the appropriate glycols with the appropriate ditosylates or dichloride in the case of the 1,2,4-triazole subcyclic unit. The crowns with proton-ionizable and lipophilic substituents were tested in liquid membrane transport systems and some of the crowns with alloxymethyl or butenyl substituents were attached to silica gel. The log K values for the interaction of these silica gel-bound macrocycles with certain metal ions were nearly the same (± 10%) as those for the association of the unbound macrocycles with the same metal ions.