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At least 865 records · Page 48Linked to original sources
PubMed2004

Catalytic photooxidation of 4-methoxybenzyl alcohol with a flavin-zinc(II)-cyclen complex.

Flavin-zinc(II)-cyclen 10 contains a covalently linked substrate binding site (zinc(II)-cyclen) and a chromophore unit (flavin). Upon irradiation, compound 10 effectively oxidizes 4-methoxybenzyl alcohol (11-OCH3) to the corresponding benzaldehyde both in water and in acetonitrile. In the presence of air, the reduced flavin 10-H2 is reoxidized, and so catalytic amounts of 10 are sufficient for alcohol conversion. The mechanism of oxidation is based on photoinduced electron transfer from the coordinated benzyl alcohol to the flavin chromophore. This intramolecular process provides a much higher photooxidation efficiency, with quantum yields 30 times those of the comparable intermolecular process with a flavin chromophore without a binding site. For the reaction in buffered aqueous solution a quantum yield of Phi = 0.4 is observed. The turnover number in acetonitrile is increased (up to 20) by high benzyl alcohol concentrations. The results show that the covalent combination of a chromophore and a suitable binding site may lead to photomediators more efficient than classical sensitizer molecules.

Journal Article↗
PubMed2005

Asymmetric diethyl- and diphenylzinc additions to aldehydes by using a fluorine-containing chiral amino alcohol: a striking temperature effect on the enantioselectivity, a minimal amino alcohol loading, and an efficient recycling of the amino alcohol.

A chiral pyrrolidinylmethanol derivative containing perfluoro-ponytails (5) was prepared from (S)-proline. The use of this perfluoro-substituted amino alcohol in catalytic asymmetric additions of organozinc reagents to aldehydes affords products with high enantioselectivities in both pure hexane and a mixture of hexane and FC-72 (perfluorohexane). Enantiomeric excesses up to 94 and 88 % ee have been achieved in Et(2)Zn and Ph(2)Zn additions, respectively. For the reactions in the biphasic solvent system a striking temperature effect was observed. Thus, when the temperature was raised from 0 to 40 degrees C the ee value of the product increased from 81 to 92 %. Furthermore, the catalyst loading could be remarkably low, and with only 0.1 mol % of amino alcohol 5 a product with 90 % ee was obtained in the Et(2)Zn addition to benzaldehyde in hexane. The perfluoro-ligand was easily recovered by simple phase separation, and until the ninth repetition its reuse proceeded without significant loss of enantioselectivity and reactivity.

Aldehydes↗
PubMed2005

Octyl-decorated Fréchet-type dendrons: a general motif for visualisation of static and dynamic behaviour using scanning tunnelling microscopy?

A detailed STM study of monolayers of 3,5-bis[(3,5-bisoctyloxyphenyl)methyloxy]benzaldehyde and 3,5-bis[(3,5-bisoctyloxyphenyl)methyloxy]benzyl alcohol adsorbed on graphite is presented. Very highly resolved scanning tunnelling microscopy images are observed at room temperature in air allowing the analysis of the conformation of the adsorbed molecules. These long-chain alkyl-decorated Fréchet-type dendrons are a powerful assembly motif and initially form a pattern based on trimeric units, assembled into hexagonal host structures with a pseudo-unit cell of seven molecules, one of which remains highly mobile. Over time, the supramolecular ordering changes from a trimeric into a dimeric pattern. The chirality arising from the adsorption onto a surface of the dendrons is discussed.

Journal Article↗
PubMed2005

Structurally diverse second-generation [2.2]paracyclophane ketimines with planar and central chirality: syntheses, structural determination, and evaluation for asymmetric catalysis.

A set of 20 novel [2.2]paracyclophane ketimines with planar and central chirality has been synthesized from enantiomerically pure and racemic 5-acyl-4-hydroxy[2.2]paracyclophane and alpha-branched chiral amines. Their X-ray structures were determined to elucidate the three-dimensional structures and the absolute configuration. The ketimines were used as catalysts in the asymmetric 1,2-addition reactions of diethylzinc with substituted benzaldehydes to furnish chiral alcohols in up to 95 % ee.

Journal Article↗
PubMed2005

Site-isolated porphyrin catalysts in imprinted polymers.

A meso-tetraaryl ruthenium porphyrin complex having four polymerizable vinylbenzoxy groups (2) has been synthesized by reaction of pyrrole with 4-(vinylbenzoxy)benzaldehyde and subsequent metalation with [Ru3(CO)12]. The porphyrin complex was immobilized by copolymerization with ethylene glycol dimethacrylate. The resulting polymer P2 was found to catalyze the oxidation of alcohols and alkanes with 2,6-dichloropyridine N-oxide without activation by mineral acids. Under similar conditions, the homogeneous catalyst 2 was completely inefficient. By using diphenylaminomethane and 1-aminoadamantane as coordinatively bound templates during the polymerization procedure, the molecularly imprinted polymers P3 and P4 have been synthesized. Compared with the polymer P2, the imprinted catalysts displayed a significantly increased activity with rate enhancements of up to a factor of 16.

Journal Article↗
PubMed2007

The Mg-oppenauer oxidation as a mild method for the synthesis of aryl and metallocenyl ketones.

Magnesium alkoxides undergo a hydride-transfer oxidation with benzaldehyde as the oxidant. This magnesium variant of the Oppenauer oxidation was used for the synthesis of polyfunctional biaryl ketones. LiCl was found to promote this reaction by enhancing the solubility of magnesium alkoxides. This mild oxidation method was especially useful for preparing ketones bearing a metallocenyl unit as well as various new ferrocenyl ketones and tricarbonylchromium complexes. This last class of ketones was reduced with the CBS catalyst (CBS=Corey-Bakshi-Shibata, diphenyl oxazaborolidine) to chiral benzhydrol complexes with high enantioselectivity enabling an asymmetric synthesis of electron-rich or -poor benzhydryl alcohols (up to 94 % ee).

Alcohols↗
PubMed2007

A general strategy for the rational design of size-selective mesoporous catalysts.

A series of functionalized mesoporous silicas with cagelike pore topology has been synthesized and screened for size-selective catalytic transformations. The aluminum-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction of differently sized aromatic aldehydes (benzaldehyde and 1-pyrenecarbox-aldehyde) has been investigated as a test reaction. The catalysts were synthesized in a two-step grafting sequence comprising pore-size engineering of mesoporous silicas (SBA-1, SBA-2, SBA-16) with long-chain alkyl dimethylaminosilanes and surface organoaluminum chemistry with triethylaluminum [{Al(CH(2)CH(3))3}2]. Size-selective reaction behavior was found for small pore SBA-1 materials, and the selectivity could be efficiently tuned by selecting a silylating reagent of appropriate size. The results are compared with the catalytic performance of a large-pore periodic mesoporous organosilica PMO[SBA-1] and the nonporous high-surface-area silicas Aerosil 300/380.

Journal Article↗
PubMed1975

Synthesis of certain 3-aminoquinazolinone Schiff's bases structurally related to some biologically active compounds.

The condensation of 2-methyl-3-amino-4(3H)-quinazolinone and 2-phenyl-3-amino-4(3H)-quinazolinone with different aldehydes is described. Reacting equimolecular amounts of these two amino compounds with p-nitrobenzaldehyde, p-hydroxybenzaldehyde, cinnamaldehyde and 5-nitro-2-furfuraldehyde diacetate afforded the respective Schiff's bases. Condensation of benzaldehyde, anisaldehyde, p-dimethylaminobenzaldehyde and o-nitrobenzaldehyde with the former quinazolinone afforded the corresponding condensation products while with the latter no condensation took place. Furthermore, condensation of cinnamaldehyde with methylaminoquinazolinone in pyridine and in glacial acetic acid afforded the mono- and di-condensation products respectively while furfural, thiophenaldehyde, resorcinaldehyde, protocatechualdehyde, veratraldehyde, and salicylaldehyde, the condensation ended in failure.

Quinazolines↗
PubMed1978

Aminoalkane sulfonic acids. Synthesis of some mitodepressive heterocyclic aminoalkane sulfonic acids.

The reaction of 2-aminopyrimidine with benzaldehyde in all applied methods yielded instead of benzal-2-aminopyrimidine (1) regardless of the procedure used, N.N'-benzilidene-bis-2-aminopyrimidine (2). The expected product benzal-2-aminopyrimidine has not been formed in any case. For this reason the synthesis of aminoalkanesulfonic acids has not been carried out by the use of Schiff bases as starting material. Reaction of aldehyde bisulfite adducts and corresponding amine, was used instead. In the syntheses where 2-aminopyridine was used as the amine part, the corresponding aminoalkanesulfonic acids were formed (3--5), while 2-aminopyrimidine under the same condition gave several reaction products (6--10). All compounds obtained were tested for their growth inhibitory activity on the seeds of cress (Lepidium sativum L.).

Aminopyridines↗
PubMed2006

Synthesis and anxiolytic activity of 1-phenyl-2-(4-aryl-1,3,4,5-tetrahydropyrido[2,3-b][1 ,4]diazepin-2-ylidene)-ethanone.

A two-step, general synthesis of 1-phenyl-2-(4-aryl-1,3,4,5-tetrahydropyrido[2,3-b][1,4]diazepin-2-ylidene)-ethanones 3-9 is presented. This synthesis employs a condensation of 2,3-diaminopyridine with benzoylacetone followed by a basic-activated cyclization reaction with substituted benzaldehydes for final closure of the seven-membered ring. Molecular diversity is fixed by appropriate aldehydes: 2-chloro-, 4-chloro-, 2-bromo-, 4-bromo-, 4-fluoro-, 4-trifluoro- and 3-bromo-4,5-dimethoxybenzaldehyde. Compounds 4, 6, 8, 9 and 10 were examined for their anxiolytic activity. The most active was the compound with the chlorophenyl substituent i.e. 1-phenyl-2-{4-(4-chlorophenyl)-1,3,4,5-tetrahydropyrido[2,3-b][1,4]diazepin-2-ylidene}-ethanone (4).

Animals↗
PubMed2005

Direct asymmetric aldol reactions catalyzed by (4R)-4-(beta-Naphthalenyl)methoxy-(S)-proline.

A novel proline derivative, (4R)-4-(beta-Naphthalenyl)methoxy-(S)-proline, was conveniently prepared from the naturally occurring (4S)-hydroxy-(S)-proline; 5 mol % of this compound efficiently catalyzes the asymmetric aldol reactions of various benzaldehydes with acetone in excess of acetone as the solvent, giving the aldol adducts in good yields with ee up to 89.8%.

Acetone↗
PubMed2005

Chiral aminonaphthol-catalyzed enantioselective carbonyl addition of diethylzinc to aromatic aldehydes high-throughput screened by CD-HPLC analysis.

Optically active aminonaphthols derivatives are obtained by condensation of 2-naphthol, substituted benzaldehyde, and (S)-methylbenzylamine under mild conditions, without side products. Their absolute configurations are determined by X-ray crystallographic analysis. The addition of diethylzinc to aromatic aldehydes is considerably accelerated by the presence of a catalytic amount of crystalline to give, after hydrolysis, the corresponding 1-phenylpropanol in good enantiomeric purity, as determined by CD-HPLC analysis as HTPS (high-throughput screening).

Aldehydes↗
PubMed2007

Polystyrene-supported N-sulfonylated amino alcohols and their applications to titanium(IV) complexes catalyzed enantioselective diethylzinc additions to aldehydes.

Crosslinked polystyrene-supported resins 4, 7a, and 7b containing N-sulfonylated beta-amino alcohol in 98, 20, and 40% loadings are prepared. Asymmetric diethylzinc additions to benzaldehyde employing titanium complexes of 10 mol % resins 4, 7a, or 7b are examined and the best performed 7a/Ti(O-i-Pr)4 catalytic system applies to various aldehydes to afford desired secondary alcohols in excellent enantioselectivities up to 95% ee. The resin 7a is reused five times, giving the product with enantioselectivities >or=86% ee and an 81% ee is obtained when the resin is used the sixth time. The used resin 7a is refreshed with 1 M HCl and the asymmetric reaction employing the regenerated resin 7a gives the product in 88% ee.

Journal Article↗
PubMed2006

Chemotopic representations of aromatic odorants in the rat olfactory bulb.

Our laboratory has characterized spatial patterns of evoked neural activity across the entire glomerular layer of the rat olfactory bulb using primarily aliphatic odorants that differ systematically in functional groups and hydrocarbon structures. To represent more fully the true range of odorant chemistry, we investigated aromatic compounds, which have a more rigid molecular structure than most aliphatic compounds and are particularly salient olfactory stimuli for humans. We first investigated glomerular patterns of 2-deoxyglucose uptake in response to aromatic compounds that differ in the nature and position of their functional groups (e.g., xylenes, trimethylbenzenes, tolualdehydes, benzaldehydes, methyl toluates, and anisaldehydes). We also studied the effects of systematic increases in the number and length of alkyl substituents. We found that most aromatic compounds activated glomeruli in the dorsal part of the bulb. Within this general area, aromatic odorants with oxygen-containing substituents favored activation of more rostral regions, and aromatic hydrocarbons activated more posterior regions. The nature of substituents greatly affected the pattern of glomerular activation, whereas isomers differing in substitution position evoked very similar overall patterns. These relationships between the structure of aromatic compounds and their spatial representation in the bulb are contrasted with our previous findings with aliphatic odorants.

Administration, Inhalation↗
PubMed1991

Responses of the L5178Y mouse Lymphoma cell forward mutation assay. V: 27 coded chemicals.

Twenty-seven chemicals were tested for their mutagenic potential in the L5178Y tk+/tk- mouse lymphoma cell forward mutation assay using procedures based upon those described by McGregor et al. (McGregor DB, Martin R, Cattanach P, Edwards I, McBride D, Caspary WJ (1987): Environ Mol Mutagen 9:143-160). Cultures were exposed to the chemicals for 4 hr, then cultured for 2 days before plating in soft agar with or without trifluorothymidine (TFT), 3 micrograms/ml. The chemicals were tested at least twice. Statistically significant responses were obtained with acid orange 10, aniline, benzaldehyde, o-chloroaniline, chlorodibromomethane, cytembena, 1,2-dibromo-4-(1,2-dibromomethyl) cyclohexane, dieldrin, lithocholic acid, oxytetracycline, phenazopyridine HCl, 1-phenyl-3-methyl-5-pyrazolone, sodium diethyldithiocarbamate, solvent yellow 14, tetraethylthiuram disulfide (disulfiram), 2,4-toluene diisocyanate, and 2,6-toluene diisocyanate. Apart from phenazopyridine HCl, acid orange 10, and solvent yellow 14, rat liver S9 mix was not a requirement for the mutagenic activity of these compounds. Chemical not identified as mutagens were N-4-acetylaminofluorene, chlorpheniramine maleate, chloropropamide, 1,4-dioxane, endrin, ethylene glycol, iron dextran, methapyrilene, sodium(2-ethylhexyl)alcohol

Animals↗
PubMed2002

Low pressure plasma treatment of poly(3-hydroxybutyrate): toward tailored polymer surfaces for tissue engineering scaffolds.

Thin films of poly(3-hydroxybutyrate) were modified by microwave ammonia plasma treatment. The results of the modification were studied by means of contact angle goniometry, ellipsometry, Fourier transform infrared-attenuated total reflection spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. To prove the presence of amino groups on the poly(3-hydroxybutyrate) surface, chemical labeling with 4-trifluoromethyl benzaldehyde was performed before X-ray photoelectron spectroscopy analysis. Under the applied plasma conditions, a hydrophilic surface with a good long-term stability was obtained.

Electron Probe Microanalysis↗
PubMed2005

Some advances in the knowledge of grape, wine and distillates chemistry as achieved by mass spectrometry.

Mass spectrometry plays a very important role in acquiring knowledge of the chemistry of grape and its derivative products. By liquid mass spectrometry, anthocyanins of grape were studied, and in hybrid grape extracts, delphinidin, cyanidin, petunidin and malvidin 3-O-(6-O-p-coumaroyl)-5-O-diglucosides were found. A semiquantitative procedure to estimate the amounts and percentages of monoglucoside and diglucoside anthocyanins without chromatography was developed. By gas chromatography mass spectrometry (GC/MS), aroma compounds of grape, wine and the distillate Italian grappa were studied, and molecular structures characterized. The representative aroma profile of Muscat grape was characterized by 23 terpenols, present in both free and bonded form, and direct correlation between aroma and genetic profile permitted to distinguish between different Muscat grape varieties. Aroma of Italian grappa resulted from and was characterized by several compounds linked to the grape variety, such as vitispiranes, terpenols, ethyl cinnamate, salicylic esters, benzaldehyde and farnesol. Synthesis of O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) derivatives and GC/MS analysis resulted in a sensitive and selective method to study carbonyl compounds at the low levels occurring in wine.

Food Technology↗