Hydroxylation hydrogen peroxide, diene

The product (6-2) from the reaction of thebaine with hydrogen peroxide can be viewed as the result from fromal 1,4 addition of two hydroxyl groups across the diene. The perspective depiction of thebaine reveals that the addition in fact occurs at the far more open face of the molecule. The product from this oxidation incorporates a new hydroxyl group at the 14(3 position and a hemiacetal at the 6 position. Treatment with a nuld acid leads to the hydrolysis of this last function and the formation of enone (6-3). 

An improved route to 2a-hydroxycholesterol has been devised as part of the preparation of 2a-hydroxy-vitamin D3 (263 R1 = R4 = R5 = R6 = H, R2 = R3 = OH).123 Hydroxylation of the A bond of cholesta-l,5-dien-3/3-ol by means of 9-borabicyclo[3,3,l]nonane followed by reaction with alkaline hydrogen peroxide produced the 2-equatorial 2a,3a-diol in 70—80% yield. The conventional four-step sequence, acetylation, bromination, dehydrobromination, and hydrolysis, gave 2a -hydroxycholesta-5,7-dien-3/3-ol which was converted into 2a-hydroxy-vitamin D3. The isomeric 2/3-hydroxy-vitamin D3 has also been reported.124 Reaction of the 1/6,2/3-oxide obtained by peroxidation of the adduct (265) with lithium aluminium hydride results in a mixture of 2/3,3/3-dihydroxycholest-5,7-diene and its 1/3,3/3-dihydroxy-epimer in the ratio 8 1. Irradiation of the former 5,7-diene furnished the expected previtamin, which on equilibration gave 2/3-hydroxy-vitamin D3 (263 R1 = R4 = R5 = R6 = H, R2 = a-OH, R3 = OH). 

Dienes may be hydroxylated at one or at both double bonds, depending on the amount of oxidants used. Cyclopentadiene, on treatment with an excess of hydrogen peroxide and osmium tetroxide as a catalyst in tert-butyl alcohol, gives a mixture of 21% of 3,5-cyclopentenediol and 61% of 1,2,3,4-cyclopentanetetrol [152. ... 

Polysaccharides that are mainly found in the gel are also a group of compounds that exhibit antioxidant activities. It was demonstrated that APS-1 (mainly composed b mannose glucose in ratio 18 5) was effective in scavenging superoxide anion radical (dose-dependant fashion), hydroxyl radical, suppressed conjugated diene formation from LDL oxidation induced by Cu, and exhibited a protective effect on hydrogen peroxide-induced injury in PC12 cells 64). Also Kardosova et al. (65) showed that in vitro experiments with acidic and neutral polysaccharides were able to prevent lipid peroxidation by scavenging hydroxyl radicals. 

Lipid peroxidation may beinitiated by any primary free radical which has sufficient reactivity to extract a hydrogen atom (Fig. 2.10) from a reactive methylene group of an unsaturated fatty acid. For example, species such as hydroxyl radicals OH, alkoxyl radicals RO peroxyl radicals ROO and alkyl radicals R may be involved. The formation of the initiating species is accompanied by bond rearrangement that results in stabilization by diene conjugate formation. The lipid radical then takes up oxygen to form the peroxyl radical. Peroxyl radicals can... 

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