5-Hydroperoxy 1,3-dienes

Selective oxidation. 5-Hydroperoxy 1,3-dienes, after protection as peroxy-acetals, undergo selective cleavage at the remote double bond. The hydroperoxides themselves are available from ene reaction of skipped dienes with singlet oxygen. 

One technique to assess lipid peroxidation utilizes second-derivative spectrophotometric analysis of cyclohexane or ethanol-reconstituted extracts to determine the cis-trans and trans-trans isomeric forms of conjugated dienes and oxodiene species within synovial fluid. Using this method, a rise in the synovial fluid concentration of conjugated oxodienes, hydroxydienes and hydroperoxy-dienes was found to follow joint exercise (Merry et al., 1991). 

In a thorough study on photooxidation of 2,5-dimethyl-2,4-hexadiene (455) it was found that 1,2-dioxene 456, 1,2-dioxetane 457, hydroperoxy dienes 458 and 459 and, when methanol was used as solvent, also hydroperoxy(methoxy)octene 460 are formed (Scheme 124) . Product distribution was found to be highly solvent dependent. These results led investigators to postulate a mechanism involving the intermediacy of perepoxide 461 and zwitterion 462 (Scheme 124). Accordingly, the product of [4-1-21-cycloaddition 456, the product of [2 + 2]-cycloaddition 457, as well as the products 458 and 459 deriving from ene-addition would originate from polar intermediates 461 and... 

As seen in Figure C4.2.1, there are two obvious methods of readily measuring LOX activity, that is, by oxygen uptake and ultraviolet (UV) absorbance of the conjugated hydroperoxy-diene product. Basic Protocol 1 describes the polarographic measurement... 

Lipoxygenases, which catalyse the oxidation of unsaturated fatty acids containing the cis,cis-l,4-pentadiene moiety to the corresponding 1 -hydroperoxy-f rans,ds-2,4-diene (Table 2.3), are widely distributed in plants and animals. The mammalian... 

In contrast to earlier literature reports, photo-oxygenation of 17/3-hydroxyoestr-5(10)-en-3-one has been shown not to be stereospecific, since a mixture of 10a- and 10/3-hydroperoxy-3-oxo-A -compounds was obtained. Thermal rearrangement of these products gave the 10a- and 10/3-hydroxy-3-oxo-A -compounds. Photo-oxygenation of 5a-cholesta-1,3-diene led only to cholesta-1,4-... 

LJnsaturated hydroperoxy acetals 189 are formed as the result of normal mono-ozonolysis in methanol of the more reactive double bond in dienes. Their subsequent ozonolysis in ether affords a 1,2-dioxane, resulting from the isopropenyl group (Scheme 64). 

Figure 26.4. Fucosterol and other structurally related sterols isolated from seaweeds. (A) Fucosterol (B) 24 -hydroperoxy-24-vinyl cholesterol (C) 29-hydroperoxystigmasta-5,24(28)-dien-3 3-ol (D) 24-ethylcholesta-4,24(28)-dien-3-one (E) 24 -hydroperoxy-24-ethylcholesta-4,28(29)-dien-3-one (F) 24-ethylcholesta-4,24(28)-dien-3,6-one (G) 24 -hydroperoxy-24-ethylcholesta-4,28(29)-dien-3,6-dione (H) 24 -hydroperoxy-6(3-hydroxy-24-ethylcholesta-4,28(29)-dien-3-one and (I) 6(3-hydroxy-24-ethyl-cholesta-4,24(28)-dien-3-one. For details readers may refer to Sheu et al. (1999). 

Lipoxygenases (LOs) are nonheme, mononuclear iron enzymes that catalyze the regio- and stereoselective conversion of polyunsaturated fatty acids with a di.di-1,4-diene functionality into products having a l-hydroperoxy-tra 5, cM-2,4-diene functionality. The mammalian LOs typically act on arachidonic acid and produce alkyl hydroperoxides that are converted into leukotrienes and lipoxins, which are involved as messengers in the inflammatory response. Plant enzymes act on linoleic acid, but the role of the product alkyl hydroperoxide is less well understood. 

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