Preparative Organic Photochemistry

Schönberg, Alexander

doi:10.1007/978-3-642-87918-0

Cited by 127 publications

(40 citation statements)

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“…Irradiation of trans-cinnamaldehyde with ultraviolet light brings about photostereoisomerization of the aldehyde (7,17), as was confirmed by the thin-layer chromatography described in Materials and Methods. Curve b in Fig.…”

Section: Resultsmentioning

confidence: 53%

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Geometric specificity of alcohol dehydrogenases and its potential for separation of trans and cis isomers of unsaturated aldehydes.

Klibanov¹,

Giannousis²

1982

Proc. Natl. Acad. Sci. U.S.A.

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The geometric specificity of three different alcohol dehydrogenases (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) (from yeast, from horse liver, and from Leuconostoc mesenteroiles) in the reduction oftrans-and cis-cinnamaldehydes has been investigated. All three enzymes display a remarkable trans specificity: they react with the trans isomer 7 to 647 times faster than with its cis counterpart. Experiments with the enzymatic reduction of 3-phenylpropionaldehyde, a saturated analog of cinnamaldehyde, have revealed that whereas tranm-cinnamaldehyde possesses the "right" configuration for the active centers ofthe alcohol dehydrogenases, the cis isomer apparently does not fit the active centers well. All three alcohol dehydrogenases studied also exhibit a marked trans specificity in the reaction with a-methylcinnamaldehyde. The geometric specificity of alcohol dehydrogenases can be used for the production of otherwise hard to synthesize cis isomers of unsaturated aldehydes from their readily available trans counterparts: trans-cinnamaldehyde was irradiated with ultraviolet light (which converted it to a mixture of trans and cis isomers) then treated with NADH and yeast alcohol dehydrogenase (which selectively reduces only trans aldehyde into the alcohol), and finally the mixture of cis-cinnamaldehyde and trans-cinnamyl alcohol was separated easily by preparative column chromatography.The separation of trans and cis isomers of unsaturated compounds is a classical problem in organic chemistry (1). In addition to its fundamental interest, this problem is also of great practical significance. Most functional properties of organic molecules are determined by their molecular geometry, and therefore these properties for trans and cis isomers are bound to be different. This can be illustrated by the following examples. Only cis isomers of substituted cinnamic acids possess plant-growth regulatory activity (2). Only trans diethylstilbestrol displays estrogenic activity (3). Balsamo et aL (4) have demonstrated that whereas trans isomers of N-alkyl-a,4-dimethylcinnamamides exhibit central nervous system-depressant activity, the corresponding cis isomers display central nervous systemstimulant activity. Particularly striking examples of dramatic differences in biological activity of trans and cis isomers can be found in the area of sex pheromones. These pheromones typically are long-chain unsaturated aldehydes, alcohols, or esters. In many cases one geometric isomer of a given pheromone is a sex attractant for one insect species, whereas its counterpart attracts another species (5).In order to take advantage of the difference in properties of the geometric isomers of unsaturated compounds, one should be able to readily prepare the trans and cis isomers separately. Unfortunately, most conventional chemical syntheses ofa given unsaturated compound usually yield just, one particular isomer, either trans or cis (6).The isomer produced can, however, be converted into a mixture of trans and cis isomers by irradiation with ultravi...

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Section: Resultsmentioning

confidence: 53%

“…The isomer produced can, however, be converted into a mixture of trans and cis isomers by irradiation with ultraviolet light (7). In principle, these mixtures can be separated by using such methods as fractional crystallization, partial precipitation, or chromatography.…”

mentioning

confidence: 99%

Geometric specificity of alcohol dehydrogenases and its potential for separation of trans and cis isomers of unsaturated aldehydes.

Klibanov¹,

Giannousis²

1982

Proc. Natl. Acad. Sci. U.S.A.

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“…The former possibility-the formation of a free radical during ethanol metabolism-was postulated by Slater [113] since many years ago. Ethanol may enter free radical reaction relatively easily [111], through the interaction with some endogenous radical; the latter could give rise to a homolytic cleavage of ethanol yielding a reducing ethoxy radical (CH 3 -CH 2 O Á ), which in the presence of some oxidant would be converted to acetaldehyde:…”

Section: Ethanol-induced Oxidative Stressmentioning

confidence: 99%

Ethanol-induced oxidative stress: basic knowledge

et al. 2009

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After a general introduction, the main pathways of ethanol metabolism (alcohol dehydrogenase, catalase, coupling of catalase with NADPH oxidase and microsomal ethanol-oxidizing system) are shortly reviewed. The cytochrome P 450 isoform (CYP2E1) specifically involved in ethanol oxidation is discussed. The acetaldehyde metabolism and the shift of the NAD/NADH ratio in the cellular environment (reductive stress) are stressed. The toxic effects of acetaldehyde are mentioned. The ethanolinduced oxidative stress: the increased MDA formation by incubated liver preparations, the absorption of conjugated dienes in mitochondrial and microsomal lipids and the decrease in the most unsaturated fatty acids in liver cell membranes are discussed. The formation of carbon-centered (1-hydroxyethyl) and oxygen-centered (hydroxyl) radicals during the metabolism of ethanol is considered: the generation of hydroxyethyl radicals, which occurs likely during the process of univalent reduction of dioxygen, is highlighted and is carried out by ferric cytochrome P 450 oxy-complex (P 450 -Fe 3? O 2 Á-) formed during the reduction of heme-oxygen. The ethanol-induced lipid peroxidation has been evaluated, and it has been shown that plasma F 2 -isoprostanes are increased in ethanol toxicity.

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“…One which crystallized more easily was identical with I in IR and PMR spectra and Rf value on TLC. According to weIl established mechanism 7 ) of photosensitized oxidation of furan, the other was expected to be V. In the PMR spectrum of V, a singlet due to C 22 -H was observed at O~~4~?-d6 6.15 ppm. Molecular weights of I and IV were not determined by their MS spectra, which showed fragment ions corresponding to M+ -60, i.e.…”

Section: New Limonoid From the Seeds Of Citrus Natsudaidaimentioning

confidence: 93%