Epoxides s. Oxido

The biosynthesis of the leukotrienes involves a series of reactions initiated by 5-lipoxygenase, which catalyzes both the oxygenation of arachidonate to 5(S)-HPETE and the subsequent dehydration of this hydroperoxide intermediate to produce the epoxide, 5(S),6(S)-oxido-7,9,l 1,15(E,E,Z,Z)-eicosatetraenoic... 

Leukotriene A4 hydrolase is a unique cytosolic epoxide hydrolase, structurally dissimilar to the cytosolic enzyme described above. Its substrate specificity is narrow, being restricted to leukotriene A4, (5(S)-trans-5,6-oxido-7,9-cis-ll,l4-trans-eicosatetraenoic acid), and related fatty acids. 

As contrasted with the vigorous catalytic hydrogenation, the reduction with LiAlH4 is unlikely to lead to the complete elimination of the oxido oxygen. Sec.-tert. epoxides form tert. carbinols in most cases, while a sec. hydroxyl group is formed by acid catalytic hydrogenation.—E a-ChoIesterol oxide acetate 3yJ,5-dihydroxycholestane. Y. 95%. (F. e. s. P. A. Plattner, H. Heusser et al., Helv. 32, 587,1070 (1949).) s. a. 4, 50 L. W. Trevoy and W. G. Brown, Am. Soc. 71, 1675 (1949)... 

Ar. ketals and thioketals, ar. and aliphatic epoxides, and ar. aziridines can be rapidly and conveniently reduced by alkali metals in liq. NHg. - E A soln. of 5 equivalents Na in liq. NHg added to a soln. of benzophenone ethylene ketal in ether, and the product isolated after 3 hrs. diphenylmethane. Y 94%. F. e., also alcohols from oxido comps., and amines from aziridines, as well as an anomalous aziridine reduction, s. E. M. Kaiser et al., J. Org. Chem. 36, 330 (1971). 

A freshly-prepared, pale yellow, soln. of AII3 in dry benzene added with stirring to a soln. of 5,6a-oxido-5a-cholestane in acetonitrile, and reaction continued for 5 min - cholest-5-ene. Y 95%. Longer reaction times were required for less reactive epoxides which initially afforded rra/i5-1,2-iodohydrins. F.e. and preferential deoxygenation s. P. Sarmah, N.C. Barua, Tetrahedron Letters 29, 5815-6 (1988). 

Dihydrolanosterol treated with m-chloroperoxybenzoic acid in chloroform 8a,9a-epoxide. Y ca. 95%.—This is the first stage of a process to shift the double bond from the 8,9- to the 9 (11)-position. The total transposition is accomplished in better than 50% yield, as compared to ca. 15% by the hest previous procedure. F. e. s. J. Fried, J. W. Brown, and M. Applehaum, Tetrah. Let. 1965, 849 mostly volatile oxido compounds s. D. J. Pasto and G. G. Gumbo, J. Org. Ghem. 30, 1271 (1965). 

---