A-Stilbene

A 500-ml. three-necked flask is fitted with a reflux condenser and a thermometer, the bulb of which reaches far enough into the flask to be covered by the liquid. A solution of 46.0 g. (0.205 mole) of a-phenylcinnamic acid (p. 70) (Note 1) in 280 ml. (307 g., 2.38 moles) of quinoline (Note 2) is added to the flask along with 4.0 g. of copper chromite.2 The reaction flask is heated by means of a mantle or an oil bath until the temperature of the reaction mixture reaches 210-220°. The mixture is kept within this temperature range for 1.25 hours. The solution is then cooled immediately and added to 960 ml. of 10% hydrochloric acid in order to dissolve the quinoline (Note 3). The product is extracted from this mixture with two 200-ml. portions of ether followed by a 100-ml. portion. The combined ether extracts are filtered to remove particles of catalyst, washed with 200 ml. of 10% sodium carbonate, and dried over anhydrous sodium sulfate. The dry solution is removed from the drying agent by filtration and heated on a steam bath to distil the ether. The residue is dissolved in a hexane fraction, b.p. 60-72° (Skellysolve B) the solution is cooled to 0° and filtered to remove /raws-stilbene, if any. The hydrocarbon solvent is removed by distillation, and the cw-stilbene is distilled. The yield is 23-24 g. (62-65%), b.p. 133-136°/10 mm., 95-97°/l mm. 1.6183-1.6193, 1.6212- 

The isomer of a-phenylcinnamic acid of m.p. 172-173° is used.3 The isomer of m.p. 137-139° yields fraws-stilbene on decarboxylation.4 

Practical quinoline containing about 10% of isoquinoline and quinaldine can be used. If the quinoline contains water, the desired temperature can be reached by distillation of a small amount of quinoline directly from the reaction mixture. 

The quinoline can be recovered by neutralization of the aqueous solution, extraction of the quinoline into ether, and distillation of the dried (over barium oxide) ether extract. 

The product obtained from this type of decarboxylation is reported to contain only about 5% of tfraws-stilbene.6 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 df-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 cfs-stilbene rather than from trans addition to fra s-stilbene. The cw-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 mpi and 8.7 X 103 at 294 mjt, quite different from Jraws-stilbene. 

---

Coupling tetra2o (7) with o-cresol has been reported to give a dye (19) which is less alkah-sensitive than Direct Yellow 4 (Cl 24890) and to have better cold-water solubiUty than Direct Yellow 12 (Cl 24895) (18). One reference is made to a stilbene laser dye (10) and two each to dyes for 1ight-po1ari2ing films (34,35) and reprographic inks (36,37). 

Especially detailed study of the mechanism of photochemical configurational isomerism has been done on Z- and A-stilbene." Spectroscopic data have established... 

The formation of exceptionally stable synthetic DNA hairpins possessing a stilbene-4,4/-dicarboxamide (Sa) linker (Scheme 1) connecting complemen-... 

Waterhouse AL and Lamuela-Raventos RM. 1994. The occurrence of piceid, a stilbene glucoside, in grape berries. Phytochemistry 37 571-573. 

Condensation of coumaric acid with malonic acid yields the basic chalcone and stilbane skeletons (see Fig. 3.6). Stilbenes are found in most vascular plants, where they exhibit fungicidal and to a lesser extent antibiotic properties. They function as both constitutive and inducible defense substances. Some stilbenes inhibit fungal spore germination and hyphal growth, whereas others are toxic to insects and parasitic nematodes (round-worms). They also possess antifeeding and nematicide properties in mammals. For example, resveratrol (a stilbene in red wine) suppresses tumor formation in mammals. 

Fig-1 General structure of a stilbene heterocyclic derivative (A), and two chalcone heterocyclic derivatives (B and C). (Dashed circles represent the location of the herocydic ring)... 

Members of the CHS/STS family of condensing enzymes are relatively modest-sized proteins of 40-47 kDa that function as homodimers. Each enzyme typically reacts with a cinnamoyl-CoA starter unit and catalyzes three successive chain extensions with reactive acetyl groups derived from enzyme catalyzed decarboxylation of malonyl-CoA.11 Release of the resultant tetraketide together with or prior to polyketide chain cyclization and/or decarboxylation yields chalcone or resveratrol (a stilbene). Notably, CHS and STS catalyze identical reactions up to the formation of the intermediate tetraketide. Divergence occurs during the termination step of the biosynthetic cascade as each tetraketide intermediate undergoes a distinct cyclization reaction (Fig. 12.2). 

In conclusion, protonation of the donor group of D-A stilbenes leads to a short wavelength shift of both absorption and fluorescence spectra and a decrease of the fluorescence quantum yield while doubly protonated D-D stilbenes exhibit a monodeprotonation in the excited state and emit an additional long-wavelength bond. 

J. F. Letard, R. Lapouyade, and W. Rettig, Relaxation pathways in photoexcited electron-rich stilbenes (D-D stilbenes) as compared to D-A stilbenes, Chem. Phys. Lett. 222, 209-216 (1994). 

The anion-radicals depicted in Scheme 3.62 were investigated by ESR and electron adsorption spectroscopy (Gregorius et al. 1992). The para isomer appears to behave completely different from the meta isomer. In full agreement with the results from MO theoretical calculations, the unpaired electron is delocalized over the whole para isomer, but confined to a stilbene unit in the meta isomer. The remaining parts in the meta isomer are uncharged. This spontaneous charge localization is not a consequence of steric hindrance, but follows from the role of the m-phenylene unit as a conjuga-tional barrier. 

Resveratrol, (Fig. 6) a stilbene present in red wine had an MIC of 25 jUg/mL for the HP strains tested, while the red wine extract had an MIC range of 25-50 /ng/mL. Interestingly, resveratrol was also more active against CagA-v strains of HP than CagA- strains. ... 

Resveratrol is another type of polyphenol, a stilbene derivative, that has assumed greater relevance in recent years as a constituent of grapes and wine, as well as other food products, with antioxidant, anti-inflammatory, anti-platelet, and cancer preventative properties. Coupled with the cardiovascular benefits of moderate amounts of alcohol, and the beneficial antioxidant effects of flavonoids, red wine has now emerged as an unlikely but most acceptable medicinal agent. 

Cuendet, M. et al., A stilbene and dihydrochalcones with radical scavenging activities from Loiseleuria procumbens, Phytochemistry, 54, 871, 2000. 

A second class of AB benzocyclobutene monomers and polymers which have been reported in the literature are those in which a benzocyclobutene and a stilbene double bond are contained within the same molecule (Fig. 36) [4, 5]. 

This is the only reported example of a chemically productive reaction between a stilbene excimer or exciplex with a third molecule. ... 

The initial example of a photochemical cross [2+2] cycloaddition reaction of a stilbene was the reaction of t-1 and 2,3-dimethyl-2-butene to yield the cyclobutane AO reported in... 

The formation of 59 and related adducts in the reactions of t-1 and several of its ring-substituted derivatives with 1,4-cy-clohexadienes (110) provides the only example of acyclic adduct formation between a stilbene and electron-rich or electron-poor alkenes (see, however, Section VI). Kaupp has proposed that... 

Hain R, Bieseler B, Kindi H, Schroder G, Stocker R. 1990 Expression of a stilbene synthase gene in Nicotiana tabacum results in synthesis of the phytoalexin resveratrol. Plant Mol Biol 15 325-335. 

Adrian M, Jeandet P, Veneau J, Weston LA, Bessis R. 1997. Biological activity of resveratrol, a stilbenic compound from grapevines, against Botrytis cinerea, the causal agent for gray mold. J Chem Ecol 23 1689-1702. 

Blair HC, Schlesinger PH. 1990. Purification of a stilbene sensitive chloride channel and reconstitution of chloride conductivity into phsopholipid vesicles. Biochem Biophys Res Commun 171 920-25. 

---