The carbon shifts induced by hydrogen bonding have been measured for complexes between benzylic alcohol and Φ or n bases (from benzene to collidine) of largely varied strengths. Linear relationships ...are obtained between corrected induced shifts and the IR frequency shifts Δν
OH
but reverse slopes result for the C-1 and C-α carbons of benzylic alcohol.
Aryl sulfotransferase IV catalyzes the 3'-phosphoadenosine-5'-phosphosulfate (PAPS)-dependent formation of sulfuric acid esters of benzylic alcohols. Since the benzylic carbon bearing the hydroxyl ...group can be asymmetric, the possibility of stereochemical control of substrate specificity of the sulfotransferase was investigated with benzylic alcohols. Benzylic alcohols of known stereochemistry were examined as potential substrates and inhibitors for the homogeneous enzyme purified from rat liver. For 1-phenylethanol, both the (+)-(R)- and (-)-(S)-enantiomers were substrates for the enzyme, and the kcat/Km value for the (-)-(S)-enantiomer was twice that of the (+)-(R)-enantiomer. The enzyme displayed an absolute stereospecificity with ephedrine and pseudoephedrine, and with 2-methyl-1-phenyl-1-propanol; that is, only (-)-(1R,2S)-ephedrine, (-)-(1R,2R)-pseudoephedrine, and (-)-(S)-2-methyl-1-phenyl-1-propanol were substrates for the sulfotransferase. In the case of 1,2,3,4-tetrahydro-1-naphthol, only the (-)-(R)-enantiomer was a substrate for the enzyme. Both (+)-(R)-2-methyl-1-phenyl-1-propanol and (+)-(S)-1,2,3,4-tetrahydro-1-naphthol were competitive inhibitors of the aryl sulfotransferase-catalyzed sulfation of 1-naphthalenemethanol. Thus, the configuration of the benzylic carbon bearing the hydroxyl group determined whether these benzylic alcohols were substrates or inhibitors of the rat hepatic aryl sulfotransferase IV. Furthermore, benzylic alcohols such as (+)-(S)-1,2,3,4-tetrahydro-1-naphthol represent a new class of inhibitors for the aryl sulfotransferase.
Various 5-arylidene 1, 3-dimethylbarbituric acid derivatives and closely related compounds were synthesized as models of redox coenzymes and used for oxidation of alcohols.Under mild neutral ...conditions, 5-arylidene 1, 3-dimithylbarbituric acid derivatives, especially those having an electron-withdrawing group on the aromatic ring, effectively oxidized allylic and benzylic alcohols to the corresponding carbonyl compounds. The relationship between the oxidizing ability and the structure of the oxidant (coenzyme model) was investigated and it was found that the electron density on the carbon-carbon double bond is a critical factor for the oxidation. In the case of the deuterium-labeled compound, the observed value of normal and primary isotope effect was 3.3 and so it was concluded that mechanism of this oxidation mainly involves the hydride transfer from the alcohol. An electrochemical investigation was also carried out and the redox potentials of the coenzyme models, 5-arylidene 1, 3-dimethylbarbituric acid derivatives and related compounds, were measured.
Under neutral conditions 5-arylidene 1, 3-dimethylbarbituric acid effectively oxidizes allylic and benzylic alcohols to the corresponding carbonyl compounds.There is a close relationship between ...oxidizing ability and electron density on the aromatic ring. The mechanism of this oxidation involves hydride transfer from the alcohol.
In the last few years, the number of synthesis approaches to metal oxide nanoparticles and nanostructures reported in literature almost exploded. They gave access to a large and rapidly growing ...collection of oxide-based nanoparticles with a wide range of compositions, monodisperse or well-defined crystallite sizes, sophisticated crystallite shapes, and with complex assembly properties. In contrast to aqueous systems, in which smallest changes in the experimental conditions result in alteration of the products, nonaqueous procedures are very robust within one system. Therefore, most of these processes are highly reproducible, easy to scale-up to gram quantities (or more) and applicable to a broad family of metal oxides. Consequently, the nonaqueous routes summarized in this book, whether they do or do not involve the use of surfactants, offer a unique opportunity not only to chemists, but also to physicists, materials scientists, and engineers to find the appropriate synthesis method for a targeted material with the desired properties.
A formal chiral synthesis of the Alangium alkaloid (-)-ankorine (-)-6 has been accomplished in the form of the synthesis of the lactam phenol (+)-14 from the (+)-trans-lactim ether (+)-5 and ...2-benzyloxy-3, 4-dimethoxyphenacyl bromide through the intermediates (+)-10 and 11. A parallel sequence of conversions starting from the (-)-trans-lactim ether (-)-5 and proceeding through the intermediates (-)-10, 24, (-)-14, (-)-15, 26, (+)-27, and (+)-28 produced the enantiomer (+)-6 of natural ankorine. For an alternative chial synthesis of (-)-6, ethyl cincholoiponate (+)-19 was acetylated and the resulting N-acetyl derivative (+)-20-was oxidized with RuO4 to give the 6-piperidone (+)-21, and 2-piperidone (-)-23 in 55% and 27% yields, respectively. The (-)-cis-lactim ether (-)-16, obtained by ethylation of (+)-21 with triethyl-oxonium fluoroborate, was then converted into (-)-13, a known precursor for the synthesis of (-)-ankorine (-)-6, in good overall yield by a "lactim ether route, " which proceeded through (+)-15 and 12.
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