By Singlet Oxygen

Single strand breaks have also been observed following exposure of DNA to 

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Classical chemiluminescence from lucigenin (20) is obtained from its reaction with hydrogen peroxide in water at a pH of about 10 Qc is reported to be about 0.5% based on lucigenin, but 1.6% based on the product A/-methylacridone which is formed in low yield (46). Lucigenin dioxetane (17) has been prepared by singlet oxygen addition to an electron-rich olefin (16) at low temperature (47). Thermal decomposition of (17) gives of 1.6% (47). 

Cyclopentadiene has also been oxidized by singlet oxygen to 4,5-epoxypenten-2-al-l, cis and trans isomers. These compounds and their hydrogenated diol products are claimed as useful intermediates as cross-linking agents, and in the production of pesticides and perfumes (34). 

Photooxidafions are also iudustriaHy significant. A widely used treatment for removal of thiols from petroleum distillates is air iu the presence of sulfonated phthalocyanines (cobalt or vanadium complexes). Studies of this photoreaction (53) with the analogous ziuc phthalocyanine show a facile photooxidation of thiols, and the rate is enhanced further by cationic surfactants. For the perfume iudustry, rose oxide is produced iu low toimage quantifies by singlet oxygen oxidation of citroneUol (54). Rose bengal is the photosensitizer. 

Oxazoles, prepared from carboxylic acids (benzoin, DCC NH4OAC, AcOH, BOSS % yield), have been used as carboxylic acid protective groups in a variety of synthetic applications. They are readily cleaved by singlet oxygen followed by hydrolysis (ROH, TsOH, benzene or K2CO3, MeOH ). 

It is interesting to note that the magnesium or zinc complexes of methyl pheophorbide a (11, M = Mg, Zn R = C02Me) or methyl pyropheophorbide a (11, M = Mg, Zn R = H) are cleaved between positions 20 and 1 by singlet oxygen, whereas in contrast nature cleaves the chlorin at the 4,5-C —C double bond.44-45a h46 The ring fission at the 4.5-C —C double bond can be achieved with the cadmium(II) complex of methyl pheophorbide (11, M = Cd R = C02Me) to produce 12.43i... 

The photooxidation of cyclopentadiene by singlet oxygen is one step of an industrial process to make 2-cyclopentene-l, 4-diol [40]. Hence the driver is a commercial one, namely to develop a continuous synthesis of this molecule. 

Photooxidation of Dienes Investigated in Micro Reactors Cas/liquid reaction 24 [CL 24] Oxidation of cyclopentadiene by singlet oxygen to 2-cyclopentene-1,4-diol... 

GL 24] [R 1] [P 26] The feasibility of safely carrying out the oxidation of cyclopentadiene by singlet oxygen to 2-cyclopentene-l, 4-diol was demonstrated [40]. The explosive intermediate endoperoxide was generated and without isolation used onsite for a subsequent hydration reaction. By reduction with thiourea the pharmaceutically important product 2-cyclopentene-l,4-diol was so obtained. 

Devasagayam, T.P.A., Steenken, S., Obendorf, M.S.W., Schultz, W.A. and Sies, H. (1991). Formation of 8-hydroxy(deoxy)guanosine and generation of strand breaks at guanine residues in DNA by singlet oxygen. Biochemistry 30, 6283-6289. 

Fig. 5.11. Kinetic curves of changes in relative electrical conductivity of ZnO film against time of treating by singlet oxygen [100]...

It is an important role plaid by singlet oxygen in oxidizing organic substances that does determine the interest in the study of interaction between 02( A ) and the surface of these substances. Application of... 

Fig. 5.16. Changes in mass of anthracene weighed sample (batch) against time during its treatment by singlet oxygen [116]...

The allylic hydroperoxides generated by singlet oxygen oxidation are normally reduced to the corresponding allylic alcohol. The net synthetic transformation is then formation of an allylic alcohol with transposition of the double bond. 

Scheme 12.17 gives some examples of oxidations by singlet oxygen. The reaction in Entry 1 was used to demonstrate that 102 can be generated from H202 and CIO-. Similarly, the reaction in Entry 2 was used to verify that the phosphite-ozone adducts... 

Foote, C. S., Y. C. Chang, and R. W. Denny. 1970. Chemistry of singlet oxygen. XI. Cis-trans isomerization of carotenoids by singlet oxygen and a probable quenching mechanism. J. Am. Chem. Soc. 92 5218-5219. 

Rodgers, M.A.J. and Bates A.L. 1980. Kinetic and spectroscopic features of some carotenoid triplet states Sensitization by singlet oxygen. Photochem. Photobiol. 31 533-537. 

The oxidation of 2,5-disubstuted furans by singlet oxygen was exploited for the synthesis of [5,5,5] and [6,5,6] bis-spiroketals <06OL1945>. An unusual regioselective photooxidation of 3-bromofuran to 2- and 3-bromo- hydroxybutenolides, as depicted below, was reported. The mechanism for the observed base-dependent regioselective deprotonation of the endoperoxide intermediate was not determined <06OL4831>. 

Beside the phosphorescence of the carbonyl compounds produced in autoxidation reactions, there is some additional luminescence by singlet oxygen 14,43) it js sometimes difficult to differentiate between emission and the longer-wavelength part of the ketone phosphorescence 38>. 

Conjugated dienes and polyenes lead to unique cases of conjugated oxidations, such as the formation of endoperoxide by singlet oxygen attack on the endo-diene, e.g. u-terpinene29. 

A palladium catalyst is used in the transformation of a siloxyfuran to a phenyl substituted furanone <00JCS(P1)3350>. Similar products, furan-2(5//)-one derivatives, are afforded through the reaction of tetra-n-butylammonium fluoride with the corresponding substituted 2-siloxyfuran <00S1878>, as well as the oxidation of 3,4-disubstituted furans by singlet oxygen . 

Alkyl-4-hydroxybutenolides. This group is present in some marine sponges and is believed to arise from 3-alkylfurans. This transformation can be realized in vitro by singlet oxygen oxidation in the presence of a hindered base such as ethyl-diisopropylamine. ... 

The reaction mechanism for the aerobic oxidation of the pz to seco-pz can be attributed to a formal 2 + 2 cycloaddition of singlet oxygen to one of the pyrrole rings, followed by cleavage (retro 2 + 2) of the dioxetane intermediate to produce the corresponding seco-pz (160). This mechanism is shown in Scheme 29 for an unsymmetrical bis(dimethylamino)pz. Further photophysical studies show that the full reaction mechanism of the photoperoxidation involves attack on the reactant by singlet oxygen that has been sensitized by the triplet state of the product, 159. As a consequence, the kinetics of the process is shown to be autocatalytic where the reactant is removed at a rate that increases with the amount of product formed. 

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