Trans-Stilbene solubility

The human cytosolic epoxide hydrolase (cytosolic EH, cEH, also known as soluble EH) has 554 amino acids (Mr 62.3 kDa) and is the product of the EPHX2 gene [49]. Its specific substrate is trans-stilbene oxide, and it appears... 

The effect of association on photochemical reactivities of stilbenes and alkyl cinnamates having poor solubilities in water has been demonstrated recently (Schemes 37 and 38) [140, 205,206]. Even at concentrations of trans-stilbene in water as low as 10 6 M, dimerization occurs efficiently. The ratios of dimers were similar to those obtained in benzene when the initial stilbene concentration is high. However, in organic solvents, geometric isomerization is the only reaction observed at low stilbene concentrations. Similar behavior... 

Figure 3. Effect of temperature on CCL solubility of trans-stilbene. c...

Deoxygenation of epoxides. n-ButyUithium (2-3 eq.) reacts with ferric chloride in THF at -78° to form a black, soluble iron species that converts epoxides into olefins in about 60-90% yield. The reaction is not stereospecific for example, the oxide of c -stilbene is converted into cu-stilbene and trans-stilbene in the ratio 89 11. ... 

The hydrogenation of olefins in supercritical carbon dioxide catalyzed by palladium nanoparticles synthesized in a water-in-C02 microemulsion was reported by Ohde et al (27). The Pd nanoparticles were prepared by hydrogen reduction of Pd ions (a PdCl2 solution) dissolved in the water core of the microemulsion. Effective hydrogenation of both C02-soluble olefins (4-methoxycinnamic acid and trans-stilbene) and a water-soluble olefin (maleic acid) catalyzed by the palladium nanoparticles in the microemulsion was demonstrated. 

For this reason, soluble polymer 296 was prepared and employed in the AD of olefins (Scheme 118) [179]. Similar yield and ee were observed for the reaction with trans stilbene than those obtained with the insoluble polymer-supported alkaloid 262 but with this soluble polymer the reaction time was very short (5h vs 48h). With other olefins used, the yield and ee were less satisfactory. The addition of diethylether allowed the precipitation of the supported alkaloid which could be reused without decrease of the catalytic activity and enantioselectivity. 

The product obtained from this type of decarboxylation is reported to contain only about 5% of /ra s-stilbene.5 A sample made according to the above directions can be treated with bromine in carbon tetrachloride at room temperature in the dark to give an 80-85% yield of the d/-dibromide which arises from trans addition to cw-stilbene. The meso-dibromide, which is very soluble and easily separated, is obtained only to the extent of 10% or less. Part of this latter product may arise from the action of bromine atoms on cw-stilbene rather than from trans addition to tfnms-stilbene. The cu-stilbene prepared by this method is readily and completely soluble in cold absolute ethanol. It freezes solid at about —5°. Its ultraviolet absorption coefficient (8) is 1.10 X 104 at 274 mil and 8.7 X 103 at 294 mp, quite different from h-aws-stilbene. 

Decarboxylation of -a-phenylcinnamic acid is effected by refluxing the acid in quinoline in the presence of a trace of copper chromite catalyst both the basic properties and boiling point (237°C) of quinoline make it a particularly favorable solvent. Z-Stilbene, a liquid at room temperature, can be characterized by trans addition of bromine to give the crystalline -dibromide. A little meso-dibromide derived from -stilbene in the crude hydrocarbon starting material is easily separated by virtue of its sparing solubility. 

The difference in the chemical structure of fraws-resveratrol and cis-piceid is that the latter has a glucose at the Rj position while the former has a hydroxyl group. This implies that the presence of the hydroxyl substituent is necessary for antitumor activity of the stilbene. The difference in activity may also be due to geometric stereochemical differences between the cis and trans double bonds and/or the poor solubility of the glucoside derivative in water which inhibits the interaction of this compound with cellular components. 

The Wittig reaction has proved to be quite versatile in the preparation of different substituted stilbenes [31-36]. This reaction is not sensitive to atmospheric oxygen, thus allowing simpler experimental procedures. It furnishes the frans-isomer in the steriospedfic reaction. Moreover, the trans-isomer can be separated from the cis-isomer in the course of reaction because it is less soluble in the reaction solvent (usually, methanol, if sodium/lithium methoxide is used as a base) and predpitates on standing. 

Water soluble p-sulfonato calbc[w]arenes (w = 8, la-lb and n=6, 2a-2b) was employed as host to control the outcome of photodimerization and photoisomerization of 4-stilbazoles [17]. Novel macrocydic and medium-size stilbenophanes tethered by silyl chains were synthesized, and their photochemical and photophysical properties were examined (Figure 5.5) [18]. Direct irradiation of macrocydic stilbenophanes stereoselectively gave intramolecular photocydoadducts, and the efficiency increased with decreasing distance between the two stilbene units. The triplet-sensitized photoreaction of stilbenophanes caused cis-trans photoisomerization. Photoreactions of as-fixed stilbenophanes under an oxygen atmosphere selectively led to phenanthrenophanes. Fluorescence quantum yields increased with the introduction of silyl substituents, and hence those of silyl-tethered stilbenophanes were larger than that of unsubstituted fraws-stilbene. Intramolecular excimer emis-... 

Organic substrates having poor solubility in water (e.g., stilbenes and alkyl cinnamates) also photodimerize efficiently in water (Scheme 122). The same reaction in organic solvents such as benzene gives mainly cis-trans... 

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