Showing papers in "Canadian Journal of Chemistry in 1994"
TL;DR: In this paper, the development of organometallic-type reactions in aqueous media is reviewed, including coupling reactions of allyl halides with carbonyl compounds mediated by zinc, or tin, or indium.
Abstract: The development of organometallic-type reactions in aqueous media is reviewed. Coupling reactions of allyl halides with carbonyl compounds mediated by zinc, or tin, or indium in aqueous media to gi...
134 citations
TL;DR: In this article, the synthesis of β-mannopyranosides by intramolecular aglycon delivery is shown to proceed with complete stereoselectivity in six separate cases.
Abstract: The synthesis of β-mannopyranosides by intramolecular aglycon delivery is shown to proceed with complete stereoselectivity in six separate cases. This strategy has been successfully applied to the ...
131 citations
TL;DR: In this paper, the authors measured densities and heat capacities for aqueous solutions of L-alanine, L-serine, and L-threonine at the standard temperature of 298.15
Abstract: The thermodynamics of amino acid systems are key to the understanding of protein chemistry. We have found that many previous studies of the apparent molar volumes and heat capacities of aqueous solutions of amino acids were conducted at the standard temperature of 298.15 K. This does not allow for the fact that most biological processes occur at temperatures removed from this standard condition.In an attempt to address this imbalance we have measured densities and heat capacities for aqueous solutions of glycine, L-alanine, L-serine, and L-threonine at 288.15, 298.15, 313.15, and 328.15 K using a Picker flow microcalorimeter. Apparent molar volumes and heat capacities, and the associated standard state partial molar properties have been calculated. Constant pressure variations of revised Helgeson, Kirkham, and Flowers equations have been fitted to calculated standard state volumes and heat capacities over the temperature range 288.15 to 328.15 K. These equations may be used to estimate standard state volu...
127 citations
TL;DR: This paper reviews PDT with an emphasis on drug development, particulary for the second generation drugs, especially BPDMA (benzoporphyrin derivative-mono acid), which is now in human clinical trials.
Abstract: Photodynamic therapy (PDT) involves the treatment of diseased tissue and cells using a photosensitizer and visible light. Such photomedical treatments have been known since the time of the ancient Egyptians but it was only just this year that this therapeutic modality was made available to modern medicine with the approval, in Canada, of Photofrin® for the treatment of bladder cancer. This paper reviews PDT with an emphasis on drug development, particulary for the second generation drugs, especially BPDMA (benzoporphyrin derivative-mono acid), which is now in human clinical trials.
96 citations
TL;DR: This work applies vacuum deposition and spectroscopic techniques previously used on synthetic organic heteropolymers, kerogens, and meteoritic organic residues to the measurement of the optical constants of poly-HCN to allow quantitative comparison with spectrophotometry of organic-rich bodies in the outer solar system.
Abstract: Matthews (1992) has proposed that HCN "polymer" is ubiquitous in the solar system. We apply vacuum deposition and spectroscopic techniques previously used on synthetic organic heteropolymers (tholins), kerogens, and meteoritic organic residues to the measurement of the optical constants of poly-HCN in the wavelength range 0.05-40 micrometers. These measurements allow quantitative comparison with spectrophotometry of organic-rich bodies in the outer solar system. In a specific test of Matthews' hypothesis, poly-HCN fails to match the optical constants of the haze of the Saturnian moon, Titan, in the visible and near-infrared derived from astronomical observations and standard models of the Titan atmosphere. In contrast, a tholin produced from a simulated Titan atmosphere matches within the probable errors. Poly-HCN is much more N-rich than Titan tholin.
85 citations
TL;DR: The biosynthesis of the phytotoxin coronatine has been investigated by administration of isotopically labeled precursors to Pseudomonas syringae pv. glycinea as mentioned in this paper.
Abstract: The biosynthesis of the phytotoxin coronatine has been investigated by administration of isotopically labeled precursors to Pseudomonas syringae pv. glycinea. The structure of coronatine contains t...
84 citations
TL;DR: In this article, it was shown that intramolecular vibrational relaxation is faster in flexible molecules when the initially prepared vibration is close to the bond about which the large-amplitude motion occurs.
Abstract: Evidence is presented to show that intramolecular vibrational relaxation (IVR) is faster in flexible molecules when the initially prepared vibration is close to the bond about which the large-amplitude motion occurs. In each of 1-pentyne, ethanol, and propargyl alcohol, IVR lifetimes are known for two different hydride stretches and in each molecule internal rotation connects gauche and trans conformers. In each case the vibration that is closer to the center of flexibility shows faster relaxation. This trend is supported by the available IVR lifetimes for other flexible molecules (hydrogen peroxide, 1-butene, n-butane, methyl formate, and propargyl amine) and for some "rigid" molecules (1-butyne, isobutane, propyne, trans-2-butene, and tert-butylacetylene). The lifetimes for the halogenated molecules, 2-fluoroethanol, 1,2-difluoroethane, trans-1-chloro-2-fluoroethane, and trifluoropropyne are all in the range expected for rigid molecules. An algorithm is presented for the consistent calculation of IVR li...
80 citations
TL;DR: In this paper, Li et al. showed that the large error in bonding energies among the late transition metals can be attributed to an overestimation of the exchange energy in the Local Density Approximation (LDA) schemes.
Abstract: Density functional methods based on the Local Density Approximation (LDA) and its nonlocal extensions (LDA/NL) are used to calculate the bond energies, as well as the bond lengths and vibrational frequencies of the high spin, open shell first-row transition metal hydride cations MH+ The D298(M+—H) LDA/NL bond energies are in good agreement with experiment for the early transition metals with errors within 5 kcal/mol However, the error increases to 6–l3 kcal/mol for the late metal hydrides An analysis based on atomic properties such as 4s ionization potentials and 4s to 3d promotion energies revealed that the large error in bonding energies among the late transition metals can be attributed to an overestimation of the exchange energy in the DFT schemes It is shown that a simple remedy, based on a thermodynamic cycle, can improve the agreement between experimental and theoretical bond energies However, simple cationic bare metal complexes such as MH+ remains a challenge to approximate DFT
80 citations
TL;DR: In this article, aqueous solutions of L-valine, L-leucine, and L-isoleucine at 288.15, 298.15 and 328.15 K were measured.
Abstract: Densities and volumetric heat capacities have been measured for aqueous solutions of L-valine, L-leucine, and L-isoleucine at 288.15, 298.15, 313.15, and 328.15 K. These data have been used to calc...
70 citations
TL;DR: In this article, the authors provide a classification and examples of N-H-π (and also O-Hπ) bonds to the aromatic π systems in organic ammonium tetraphenylborates that would serve as refe...
Abstract: The aim of this investigation is to provide a classification and examples of N—H …π (and also O—H …π) bonds to the aromatic π systems in organic ammonium tetraphenylborates that would serve as refe...
68 citations
TL;DR: In this paper, a range of Ni-SiO2 catalysts have been prepared by homogeneous precipitationdeposition and impregnation techniques and modified with aqueous solutions of R-(+)-tartaric acid (TA) to induce enantioselectivity in the asymmetric hydrogenation of a prochiral β-ketoester (methyl acetoacetate) to a β-hydroxyester ((R)-(−)-methyl 3-hydroxbutyrate).
Abstract: A range of Ni–SiO2 catalysts have been prepared by homogeneous precipitation–deposition and impregnation techniques and modified with aqueous solutions of R-(+)-tartaric acid (TA) to induce enantioselectivity in the asymmetric hydrogenation of a prochiral β-ketoester (methyl acetoacetate) to a β-hydroxyester ((R)-(−)-methyl 3-hydroxybutyrate). The effects of catalyst precursor preparation, nickel loading, and precalcination on the reduction of the precursor were examined and the nature of the resultant nickel particle size distribution is described. The influence of metal–support interactions on the uptake of TA was investigated and data on the corrosive metal leaching and the consequent changes in metal dispersion are presented. Modification of the catalysts with TA not only induced enantioselectivity, but also increased the turnover frequency by up to 15 times that observed for the unmodified surface. The amount of TA adsorbed and the fractional surface coverage by TA is related to the degree of enantio...
TL;DR: In this paper, high resolution 3D images of the molecular body and tertiary structure elements of insulin were computed using the new Molecular Electron Density Lego Assembler (MEDLA) method.
Abstract: Detailed, ab initio quality electron density calculations are reported for the elements of the tertiary structure of bovine insulin, a protein containing 773 atoms in 51 residues. The high resolution 3D images of the molecular body and tertiary structure elements of insulin are computed using the new Molecular Electron Density Lego Assembler (MEDLA) method. The high, intermediate, and low electron density images show detailed, intricate shape features not revealed before. The MEDLA technique serves as a computational microscope for chemical, biochemical, pharmaceutical, and drug design applications.
TL;DR: Condensation of pyrrole with a benzaldehyde and 4-pyridinecarboxaldehyde mixture yields the six possible meso-substituted phenyl or pyridyl porphyrins as discussed by the authors.
Abstract: Condensation of pyrrole with a benzaldehyde and 4-pyridinecarboxaldehyde mixture yields the six possible meso-substituted phenyl or pyridyl porphyrins. Nitration of four of these has yielded 13 oth...
TL;DR: Homo- and hetero-nuclear chemical shift correlation techniques and nuclear Overhauser enhancement experiments led to the unambiguous assignment of the 1H and l3C resonances associated with each of the component glycosyl residues and established their sequence within the backbone oligosaccharide as shown.
Abstract: The cell-surface lipopolysaccharide produced by Moraxella catarrhalis serotype A is composed of a hydrophobic lipid A moiety and an oligosaccharide, but lacks high-molecular-weight O-polysaccharide...
TL;DR: The density and shear viscosity of mixtures of tert-butyl alcohol (BuOH) and tert-butylamine (TBA) with water have been determined for various temperatures (288 to 318 K for H2O+BuOH and 288 to 308 K for TBA) over the whole composition range.
Abstract: The density and shear viscosity of mixtures of tert-butyl alcohol (BuOH) and tert-butylamine (TBA) with water have been determined for various temperatures (288 to 318 K for H2O + BuOH and 288 to 308 K for H2O + TBA) over the whole composition range. Excess molar volumes and apparent molar volumes of the components of each system were calculated from the density data. In both systems the apparent molar volume of the organic component passes through a minimum in the water-rich region. Both systems exhibit large negative excess molar volumes which are essentially independent of temperature at all compositions. The two systems show pronounced maxima in their shear viscosity isotherms.
TL;DR: In this article, 1-(2-Bromobenzyl)-2-alkanesulfonylpyrroles (1c, 1d) undergo oxidative radical cyclization with partial or complete reductive desulfonylation to the...
Abstract: 1-(2-Bromobenzyl)-2-alkanesulfonylpyrroles (1c, 1d) and 1-(4-bromobutyl)-2-methylsulfonfylpyrrols (8) undergo oxidative radical cyclization with partial or complete reductive desulfonylation to the...
TL;DR: Water-soluble, meso-substituted porphyrins are synthesized by sulfonation or methylation of the phenyl or pyridyl groups, respectively, of some non-water soluble functionalized porphrin this article.
Abstract: Water-soluble, meso-substituted porphyrins are synthesized by sulfonation or methylation of the phenyl or pyridyl groups, respectively, of some non-water-soluble functionalized porphyrins that we h...
TL;DR: Kinetic studies with plant HSS documented that the putrescine semialdehyde moiety of spermidine is a substrate of HSS, and studies with deuterated and 14C-labeled substrates revealed that in the presence of putRescine sperMidine is an HSS substrate.
Abstract: sym-Homospermidine, the first pathway-specific intermediate of pyrrolizidine alkaloid (PA) biosynthesis, is formed from two moles of putrescine in an NAD+-dependent reaction catalyzed by homospermi...
TL;DR: In this article, metal-free phthalocyanine derivatives were converted to their zinc derivatives using trifluoroacetic acid and showed that all the 2,9,16,23-tetrasubstituted isomers were formed as pure single isomers.
Abstract: 2,9,16,23-Tetra-p-n-butylbenzyloxy-, 2,9,16,23-tetradiphenylmethoxy-, 2,9,16,23-tetramethoxymethoxy-, and 1,8,15,22-tetra-p-n-butylbenzyloxyphthalocyanines were synthesized from the appropriate phthalonitriles. Metal-free phthalocyanines were converted to their zinc derivatives. Cleavage from the appropriate precursor with trifluoroacetic acid produced 2,9,16,23-tetrahydroxyphthalocyanine and 1,8,15,22-tetrahydroxyphthalocyanine and their zinc derivatives. NMR spectroscopy revealed that all the 2,9,16,23-tetrasubstituted phthalocyanines are the usual mixtures of the 2,9,16,23, 2,9,16,24, 2,9,17,24, and 2,10,16,24 isomers, but the two 1,8,15,22-tetrasubstituted phthalocyanines were formed as pure single isomers.
TL;DR: The conformations of the biologically active taxol analogs Taxotere®, 3R, 4R, and 4S, and the biologically inactive analog 3S were evaluated in CDCl3 and DMSO–water solution using 1H NMR coupling constant and NOESY data and molecular modeling.
Abstract: The conformations of the biologically active taxol analogs Taxotere®, 3R, 4R, and 4S, and the biologically inactive analog 3S were evaluated in CDCl3 and DMSO–water solution using 1H NMR coupling constant and NOESY data and molecular modeling. The solution structures of Taxotere® were very similar to those detected previously for taxol. The A-ring side chain conformations of analogs 3 and 4 could not be defined with the same precision as had been possible for taxol, but the conformational possibilities could be significantly limited by the data. Analogs 3R, 4R, and 4S (but not 3S) can mimic the dominant conformation of taxol in chloroform, but no logical relationship between biological activity and aqueous solution conformation could be detected.
TL;DR: Two different chemoenzymatic enantioselective syntheses of baclofen are reported based on the distinction between enantiotopic ester groups in compounds bearing a prochiral centre.
Abstract: We report two different chemoenzymatic enantioselective syntheses of baclofen based on the distinction between enantiotopic ester groups in compounds bearing a prochiral centre. In the first approach, the key step is the highly stereoselective enzymatic hydrolysis of dimethyl 3-(4-chlorophenyl)glutarate by chymotrypsin in an aqueous medium. In the second approach, the key step is the enzyme-catalyzed esterification of 2-(4-chloropheny 1)-1,3-propanediol by acetic anhydride in the presence of a lipase in an organic medium.
TL;DR: Reaction of alkyl 2-alkynoates with sodium iodide in acetic acid provides good to excellent yields of the correspondingAlkyl (Z)-3-iodo-2-alkenoates.
Abstract: Reaction of alkyl 2-alkynoates with sodium iodide (1.6–5.5 equiv.) in acetic acid (6.2–13 equiv.) at 115 °C provides good to excellent yields of the corresponding alkyl (Z)-3-iodo-2-alkenoates.
TL;DR: In this article, the complete set of minimum energy (i.e., stable) conformations of For-AlaAla-NH2 (containing three peptide bonds) was computed by ab initio geometry optimization.
Abstract: This paper reports the complete set of minimum energy (i.e. stable) conformations of For-Ala-Ala-NH2 (containing three peptide bonds), computed by ab initio geometry optimization. A more confident structure and relative energy comparison of the 49 different relaxed geometries was possible using the HF/3-21G method as compared to empirical (force field) methods. The analysis of the different conformers resulted in a useful structure database, incorporating 30 different β-turns, which will have some relevance to the description of peptide folding. Spectroscopic (e.g. NMR) consequences of the reported ab initio calculations are also discussed, and a 3D-structure assignment method for proteins is provided.
TL;DR: Three potential intermediates in polyketide formation were reexamined as their corresponding N-acetylcysteamine (NAC) thioesters and a remarkably high 22% intact incorporation of [1-13C]hexanoic acid was given.
Abstract: Earlier work in this laboratory has shown the intact incorporation of [1-13C]hexanoate into averufin (1), a key intermediate in aflatoxin B1 biosynthesis. Parallel experiments with equimolar amount...
TL;DR: In this paper, the pKa values for uracil (U) (pK1 and pK2), thymine (T), and cytosine (C) were determined from emf measurements of Harned-Ehler type cells comprising H2 and Ag-AgI electrodes at five equidistant temperatures ranging from 15-35 °C.
Abstract: The protonation/deprotonation constants for uracil (U) (pK1 and pK2), thymine (T) (pK1) and cytosine (C) (pK1 and pK2) in water have been determined from emf measurements of Harned–Ehler type cells comprising H2 and Ag–AgI electrodes at five equidistant temperatures ranging from 15–35 °C. The pKa values were fitted in the temperature equation pKa = AT−1 + B + CT by the method of least squares and the standard free energies (ΔG0), entropies (ΔS0), and enthalpies (ΔH0) of protonation/deprotonation processes in water were evaluated using the values of the coefficients A, B, and C of the respective acids. The second step deprotonation constant for T was determined using precise spectrophotometric method. The results have been duly compared with the existing literature data and are also shown to derive important reflections on the sites of protonation/deprotonation in the light of pK values of some acids and bases of comparable functional groups and especially the entropies of protonation/deprotonation of the ...
TL;DR: In this article, five new compounds related to the neurotoxin domoic acid have been characterized by spectroscopic methods, including a diastereoisomer and four hydrogenation products.
Abstract: Five new compounds related to the neurotoxin domoic acid have been characterized by spectroscopic methods. They include a diastereoisomer that occurs naturally with domoic acid in mussels and four hydrogenation products. The stereochemistry of the two epimeric tetrahydro derivatives could not be assigned on the basis of the NMR data alone because of high conformational flexibility. However, a clear-cut assignment was possible by molecular modelling in combination with the NMR data.
TL;DR: The C-aryl glucals 17−31 have been prepared by the palladium-catalyzed cross coupling of 1-tributylstannyl-3,4,6-tri-O-(tert-butyldimethylsilyl)-D-glucal (11) and aryl bromides as discussed by the authors.
Abstract: The C-aryl glucals 17–31 have been prepared by the palladium-catalyzed cross coupling of 1-tributylstannyl-3,4,6-tri-O-(tert-butyldimethylsilyl)-D-glucal (11) and aryl bromides. The major by-produc...
TL;DR: In this article, the new complex [Ag2(hfac)2(μ-dmpm)2] (hfac=hexafluoroacetylacetonato, dmpm=Me2PCH2PMe2) has been prepared and characterized both spectroscopically and by X-ray structure determination.
Abstract: The new complex [Ag2(hfac)2(μ-dmpm)2] (hfac = hexafluoroacetylacetonato, dmpm = Me2PCH2PMe2) has been prepared and characterized both spectroscopically and by an X-ray structure determination (orthorhombic, Pbca (No. 61), a = 9.960(2), b = 14.694(3), c = 22.548(3) A, Z = 4, R = 0.0495, Rw = 0.0532). The data indicate that the hfac− ligands have mostly ionic character and it is suggested that this may be responsible for the low volatility of complexes [Ag(hfac)Ln] compared to [Cu(hfac)Ln]; these complexes are of interest as precursors for chemical vapour deposition of silver.
TL;DR: In this article, the commercially available methyl (2S)-3-hydroxy-2-methyl propionate 5 (96% ee) readily underwent potassium carbonate in...
Abstract: (3R)-2-(N-Benzylideneamino)-4-chloro-3-methylbutyronitrile 3, prepared from the commercially available methyl (2S)-3-hydroxy-2-methyl propionate 5 (96% ee), readily underwent potassium carbonate in...
TL;DR: In the density domain approach, chemical bonding between fragments of a molecule is characterized by a finite sequence of density domains within a wide range of density values and by the correponding sequence of topological patterns of the mutual interpenetration of these fragments.
Abstract: A density domain (DD) is the formal body enclosed by a molecular isodensity contour (MIDCO) surface. Individual nuclear neighborhoods and various formal molecular fragments can be regarded as fuzzy moieties of electron densities, dominated by one or several nuclei. Such a fuzzy fragment involves a whole range of density values, hence it cannot be described by a single MIDCO, but it can be represented by a sequence of density domains. Within the chemically important range of density values, there are only a finite number of topologically different bodies of density domains. In the Density Domain Approach, chemical bonding is described by the interfacing and mutual interpenetration of local fuzzy charge density clouds. The bonding between fragments of a molecule is characterized by a finite sequence of density domains within a wide range of density values and by the correponding sequence of topological patterns of the mutual interpenetration of these fragments. In earlier works, the DD approach was advocate...