Showing papers in "Canadian Journal of Chemistry in 2000"

The Suzuki, the Heck, and the Stille reaction — three versatile methods for the introduction of new C—C bonds on solid support

Abstract: Metal-catalyzed coupling reactions are very efficient and reliable methods for the introduction of new carbon-carbon bonds onto molecules attached to a solid support. This review summarizes recent advances in utilizing the three most used methods, the Suzuki reaction, the Heck reaction, and the Stille reaction, in the field of solid phase organic synthesis resulting in small organic molecule libraries.Key words: metal-catalyzed coupling reactions, carbon-carbon bonds, solid phase synthesis, combinatorial chemistry, drug discovery.

Isolation of bioactive 5α,8α-epidioxy sterols from the marine sponge Luffariella cf. variabilis

Abstract: The lipid extract of the marine sponge Luffariella cf. variabilis from Mayotte (Indian Ocean) has proven to be an extraordinarily rich source of a wide variety of unusual steroids belonging to the ...

The reaction between hydrazines and β-dicarbonyl compounds: proposal for a mechanism

Abstract: The reaction between aryl or heteroarylhydrazines with fluorinated β-diketones (CF3COCH2COR) yields a variety of 3-, 5-, and 3,5-trifluoromethylpyrazoles and 5-trifluoromethyl-5-hydroxy-Δ2-pyrazoli...

Synthesis and reactivity of the stable silylene N,N'-di-tert-butyl-1,3-diaza-2-sila-2-ylidene

Abstract: The synthesis and several reactions of the stable silylene 1 (N,N'-di-tert-butyl-1,3-diaza-2-sila-2-ylidene) are reported. Overreduction of 1 with alkali metals results in the formation of a dimeri...

Heck reaction using palladium complexed to dendrimers on silica

Abstract: Polyamidoamine dendrimers, constructed on the surface of silica, were phosphonated using diphenylphosphinomethanol (prepared in situ) and complexed to form a palladium-dimethyl TMEDA complex. This catalyst was found to be effective in the Heck reaction of aryl bromides with both butyl acrylate and styrene, affording coupling products in moderate to good yields. The heterogeneous palladium catalyst can also be recycled and reused with only moderate reduction in activity.

Reactions of the radical cation derived from 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·+) with amino acids. Kinetics and mechanism

Abstract: Stable free radicals derived from 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·+) have been extensively employed to monitor the antioxidant capacity of biological fluids and beverages. Besides reacting with typical antioxidants (such as phenols or thiols) these radicals react with a variety of hydrogen or electron donors. The present work reports on the kinetics and mechanism of these radical reactions with several amino acids. Reaction rates notably increase when the pH of the media increases and, when measured under similar conditions, follows the ordercysteine > > tryptophan > tyrosine > histidine > cystineThe kinetics of the process is interpreted in terms of a mechanism comprising an initial pH dependent reversible step, followed by secondary reactions of the substrate derived radical with itself or with another ABTS·+; this simple three-step mechanism leads to very complex kinetic expressions. The specific rate constants of several of the elementary steps were determined by working un...

Electrocatalytic hydrogenation of lignin models at Raney nickel and palladium-based electrodes

Abstract: The electrocatalytic hydrogenation (ECH) of β-O-4 lignin model compounds has been carried out at constant current at Raney nickel and palladium-based cathodes in aqueous sodium hydroxide solution a...

Synthetic applications of the ruthenium-catalyzed hydrogenation via dynamic kinetic resolution

Abstract: This review summarizes some recent work in the field of homogeneous ruthenium-catalyzed hydrogenation via dynamic kinetic resolution. The hydrogenation reaction of various α-substituted β-oxo ester...

Antiviral activity of arylnaphthalene and aryldihydronaphthalene lignans

Abstract: A practical method for large scale synthesis of 1-arylnaphthalene and 1-aryl-1,2-dihydronaphthalene lignans is described. The method makes use of the classic Stobbe condensation followed by regiose...

A facile new procedure for the deprotection of allyl ethers under mild conditions

Abstract: A novel isomerization of O-allyl glycosides into prop-1-enyl glycosides was observed instead of cross-metathesis during an olefin metathesis reaction using Grubbs' ruthenium benzylidene catalyst (C...

Silver-catalyzed asymmetric amination of silyl enol ethers

Abstract: Catalytic amination of silyl enol ethers with azo diester compounds was investigated. It was shown that Cu(OTf)2 or AgOTf had high catalytic activity and that AgOTf was the most efficient among the...

Thermodynamics of mixtures with strongly negative deviations from Raoult's law. Part 3. Application of the DISQUAC model to mixtures of triethylamine with alkanols. Comparison with Dortmund UNIFAC and ERAS results

Abstract: Binary mixtures of triethylamine (TEA) and alkanols have been investigated in the framework of DISQUAC. The systems are built by three contacts: aliphatic–hydroxyl, aliphatic–nitrogen, and hydroxyl...

Atomic properties of selected biomolecules. Part 1. The interpretation of atomic integration errors

Abstract: Reliable atomic properties can be obtained via the theory of "Atoms in Molecules" (AIM) via integration over a finite volume. These integrations are challenging because of the variety and complexity of the shape of the AIM atoms. In practice the integration of a large number of atoms (100-1000, sampled from many molecules) yields integration errors L(Ω) of varying magnitude. We prove that it is impossible to predict the size of an angular Gauss- Legendre grid (outside the β sphere) that guarantees a pre-set error. Hence it is incorrect to assume that a large grid (∼23 000 angular grid points) will automatically yield a low L(Ω) value. The erratic relationship between the integra - tion error and the grid size prompts a statistical interpretation of atomic integration, at a purely practical level. More importantly we have investigated the relationship between L(Ω) and seven atomic properties which include volume, energy, and the magnitudes of five electrostatic multipole moments. The electronic population (N(Ω)) and the volume (v(Ω)) of carbon is linearly correlated with L(Ω), enabling the interpolation or extrapolation of N(Ω) and v(Ω). Other properties of carbon and other atoms (N, O, and S) yield low correlation coefficients but occasionally trends can be observed. For example, we find that some properties are systematically underestimated if L(Ω) is negative. This work has led to an estimate of safe error bars of atomic properties for atoms occurring in biological molecules with reason - ably sized integration grids. The most stable properties were found to be the energy and the population. Finally, we have observed that the influence of the grid orientation is less if L(Ω) is small, and that population and energy are the least affected.

Reactions of the stable bis(amino)silylene Si[{N(CH2tBu)}2C6H4-1,2] with group 3 or lanthanide metal organic compounds. Crystal structures of [Ln(η5-C5H5)3Si{[N(CH2tBu)]2C6H4-1,2}]·C7H8 (Ln = Y or Yb)

Abstract: Treatment of the thermally stable aminosilylene Si[{N(CH2tBu)}2C6H4-1,2] [= Si(NN)] with a tris(cyclopentadienyl)- group 3 or -lanthanide metal compound LnCp3 (Cp = η5-C5H5 and Ln = Y or Yb) in tol...

The directed ortho metalation - palladium catalyzed cross coupling connection. A general regiospecific route to 9-phenanthrols and phenanthrenes. Exploratory further metalation

Abstract: A new general and regiospecific synthesis of 9-phenanthrols (1 +2 3 4, Scheme 1, Table 1) proceeding by a Directed ortho Metalation (DoM), Suzuki-Miyaura cross coupling, and a new LDA-mediated Dire...

Excited state intramolecular proton transfer in 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole: effects of solvents and pH

Abstract: The solvent dependent study of absorption, fluorescence, and fluorescence excitation spectra of 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole (HPNI) have indicated the presence of different rotamers and tautomers in the So and S1 states. Similarity of the absorption and fluorescence spectra of HPNI in protic solvents with those of 2-(2'-methoxyphenyl)-1H-naphth-[2,3-d]-imidazole (MPNI) suggests that the normal emission is observed from the rotamers 2 and 4, whereas the tautomer emission is observed from the tautomer 3, formed by the excited state intramolecular proton transfer (ESIPT) in the rotamer 1 (Scheme 1). Ground state geometries of rotamers 1, 2, and the tautomer 3 were optimized using AM1 method. The results show that the rotamer 2 is the most stable and its stability further increases in polar and protic solvents due to the dipolar solvation interaction. The increase in the fluorescence quantum yield of the normal band when methanol or water is added to dioxane is due to: (i) the formation of...

Titrage infrarouge de l'acide phosphorique

Abstract: The titration of phosphoric acid by sodium hydroxide was performed by infrared (IR) spectroscopy with the objective of obtaining the infrared spectra of the pure ionic species and determining their abundance as a function of pH. In the series of spectra, taken in the pH range of 0.18-13.4, the subtraction of neutral water, acidic water, and basic water was made. Factor analysis (FA) was then applied to the series of spectra to obtain the objective. First, we found the four most abundant species : H3PO4 (pH 0-4), H2PO-4 (pH 0-9), HPO4-2 (pH 4-14), and PO4-3 (pH 9-14). Secondly, we found three complexes in small quantities : H3PO4–H2PO–4(pH 0-4),H2PO–4–HPO–24 (pH 4-9), and HPO–24–PO–34 (pH 9-14). The equilibrium constants of these species with the parent molecules are 0.65, 0.63, and 0.4 L/mol, respectively. Thirdly, we found residual water that was closely bound to the ionic species which formed hydrates. The pKa values obtained from the IR titration were used to obtain the theoretical concentration of the...

Ethylene-polymerization by surface supported Cr(IV) species: possible reaction mechanisms revisited by theoretical calculations

Abstract: Possible reaction mechanisms of olefin polymerization catalyzed by surface supported Cr(IV) species have been investigated by first principles density functional theory (DFT). Pathways starting from neutral alkylidene or bisalkyl complexes were found to suffer from high ethylene insertion barriers, whereas a cationic system formed by protonation of the alkylidene show a low barrier for chain propagation.Key words: density functional theory, alkylidene, olefin polymerization, Cr(IV) species.

AIM study on the transferability of the oxygen atom in linear ethers

Abstract: The integrated values of the electron population, electron energy, nucleus–electron potential energy interaction, dipole moment and volume of the oxygen atoms, and the main properties of the O—C bo...

Catalysis of the methanolysis of acetylimidazole by lanthanum triflate

Abstract: Methanolysis of acetylimidazole (1) and N-acetylimidazolepentamine-Co(III) (2) was found to be markedly accelerated in the presence of La(OTf)3. Potentiometric titration of a solution of La3+(OTf-)...

Efficient synthesis of optically active 2-amino-2'-diphenylphosphino-1,1'-binaphthyl and its derivatives

Abstract: Optically active 2-amino-2'-diphenylphosphino-1,1'-binaphthyls having various functional groups, such as amino, alkoxycarbonylamino, acylamino, mono- and dialkylamino, and sulfonylamino at C2 posit...

Infrared titration of aqueous NaOH by aqueous HCl

Abstract: The titration of NaOH by HCl is achieved through infrared spectral measurement of the various mixtures Factor Analysis (FA) is used to separate the spectra Four principal spectra were necessary t

A new strategy for synthesis of attached rings

Abstract: The first investigation of the use of pinacol-terminated Prins cyclizations to form attached rings is reported. Treatment of triisopropylsilyl ethers of (Z)- or (E)-[2-(6,6-dimethoxyhexylidene)cycl...

The insertion of germylene into the HH bond; rate constant limits and thermochemistry. Ab initio and DFT calculations on the reactions of GeH2 and SiH2 with H2

Abstract: The technique of laser flash photolysis in the gas-phase has been used to set limits on the rate constants for the bimolecular reaction of germylene (GeH2) with deuterium (D2) at both ambient and elevated temperatures (585 K). These limits show that the activation energy for the insertion of GeH2 into the H—H bond is at least 19 (±6) kJ mol–1. Thermochemical arguments place the activation energy approximately in the range 63–84 kJ mol–1. DFT B3LYP/6-311++G(3df,2pd) and ab initio QCISD(T)/6-311G++(3df,2pd)//QCISD/6-311G(d,p) calculations have been carried out on the potential energy surfaces of reactions ZH2 + H2 ZH4 (Z= Ge, Si). Both methods predict the same mechanisms for germylene and silylene insertion which include formation of loose prereaction complexes and transition states of similar structure. The prereaction complex is only about half as strong in the case of germylene (ΔH (298 K) = –9 (–11) kJ mol–1) as in the case of silylene (ΔH (298 K) = –16 (–21) kJ mol–1) (QCISD values cited with B3LYP val...

The effect of aspirin-HSA complexation on the protein secondary structure

Abstract: This study was designed to determine the secondary structure of human serum albumin (HSA) in the presence of aspirin in H2O and D2O solutions at physiological pH, using aspirin concentrations of 0.0001-5 mM with final protein concentration of 2% w/v. UV-vis spectra and Fourier transform infrared (FTIR) difference spectroscopy with its self-deconvolution, second derivative resolution enhancement, and curve-fitting procedures were applied to characterize the drug binding mode, the binding constant, and the protein secondary structure in the aspirin-HSA complexes. Spectroscopic evidence showed that no aspirin-protein interaction occurs at very low drug concentration (0.0001 mM), whereas at higher drug contents (0.001-0.1 mM) the aspirin anion binding (H-bonding) is mainly through the e-amino NH3+ group with overall binding constant of K = 1.4 × 104 M-1. At high drug concentrations (1-5 mM), acetylation of Lys-199 was observed. Aspirin binding results in protein secondary structural changes from that of the α...

Solution multinuclear (31P,111Cd,77Se) magnetic resonance studies of cadmium complexes of heterocyclic aromatic thiones and the structure of [tetrakis(2(1H)-pyridinethione)cadmium] nitrate, [Cd(C5H5NS)4](NO3)2

Abstract: The complex salts CdL4(O3SCF3)2 (L = 2(1H)-pyridinethione (Py2SH), 4(1H)-pyridinethione (Py4SH), or 2(1H)-quinolinethione (Q2SH)) have been synthesized by the stoichiometric reaction of Cd(O3SCF3)2

Trans alkenylpyridine and alkenylamine complexes of platinum

Abstract: Addition of cis-cyclooctene (coe) to K2PtCl4 gives trans-[PtCl2(coe)]2 (1), which reacts with excess coe to give trans-PtCl2(coe)2 (2). Compound 2 was characterized by an X-ray diffraction study and crystals were found to be triclinic, a = 5.7838(5), b = 7.4347(6), c = 9.9972(9) A, α = 83.924(1), β = 87.844(2), γ = 73.546(1)°, Z = 1, with space group P1-. Addition of 4-vinylpyridine (4vp) to 1 gave trans-PtCl2(4vp)2 (5) which was also characterized by an X-ray diffraction study. Crystals of 5 were monoclinic, a = 8.2255(6), b = 12.8254(10), c = 6.9624(5) A, β = 98.8230(10)°, Z = 2, with space group P21/c. Although alkenylamines react with 1 to give a mixture of products, addition of one equivalent of apve (H2NCH2CH2CH2OCHβCH2) to 1 cleanly afforded the organometallic product trans-PtCl2(coe)(thmo) (thmo = tetrahydro-2-methyl-1,3-oxazine) arising from a metal-catalyzed intramolecular hydroamination of the starting alkenylamine. Initial investigations into the functionalization of metal complexes containing...

Synthesis of nanocrystalline Cu2 xSe at room temperature by γ-irradiation

Abstract: Ten nm nonstoichiometric compound Cu2 – xSe was firstly synthesized at room temperature by γ-irradiation, using sodium selenosulfate as the selenium source. The influence of the coordination of cop...

On diastereomeric perturbations

Abstract: For more than a century, organic chemists have been playing in Nature's laboratory. Their first goal was to understand the organization of atoms in the living matter and then to reproduce it by syn...

New abietane diterpenoids from the cones of Larix kaempferi

Abstract: A new podocarpane diterpene, 7α,15-dihydroxypodocarp-8(14)-en-13-one (1) and eight new abietane diterpenes, abiet-8(14)-en-7α,13β,15,18-tetraol (2), 7α,13β,15-trihydroxyabiet-8(14)-en-18-oic acid (3), 13β,18-dihydroxyabiet-8(14)-en-7-one (4), 13β,15,18-trihydroxyabiet-8(14)-en-7-one (5), 7-oxo-13β-methoxyabiet-8(14)- en-18-oic acid (7), abiet-8(14)-en-7α,12α,13β,18-tetraol (8), 7α,12α,13β-trihydroxyabiet-8(14)-en-18-oic acid (9), and abiet-8(14)-en-7α,12α,13β,15,18-pentaol (10) were isolated from the CHCl3 extract of the cones of Larix kaempferi. Their structures were determined on the basis of chemical and spectral evidence. The inhibitory effects of compounds 1-4 and 7-9 on Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), were examined for a primary screening for anti-tumor promotors. Key words: Larix kaempferi, Pinaceae, cones, abietane, EBV-EA.