Diol epoxides preferences

The conformations of the 1- and 3-nitro-BaP metabolites were determined through analysis of their NMR spectra (145-146). Both 1- and 3-nitro-BaP-trans-7,8-dihydrodiols existed predominantly in quasi-diequatorial conformations, which corresponds to the preferred conformation of the proximate carcinogen BaP-trans-7,8-dihy-drodiol (149). This suggests that these dihydrodiol metabolites may be converted into electrophilic diol epoxides and in support of this contention, the stereochemistries of 1- and 3-nitro-BaP-... 

It turns out that epoxidation prefers the more substituted alkene in the ring. The epoxide 31 can then be opened to the diol 32 and cleaved with periodate to give 28. The ketoaldehyde 28 was not isolated but cyclised immediately.4... 

Geadntov, N.E., and Sdcchitano, D.A. (2003) Human RNA polymerase II is partially blocked by DNA adducts derived from tumorigenic benzojc] phenanthrene diol epoxides relating biological consequences to conformational preferences. Nucleic Acids Res.,... 

The novel bay-region diol epoxide isomers (93) have proved to be remarkably biologically active, despite their relative lack of reactivity towards hydrolysis (as expected from simple PMO calculations). Both diastereo-isomers prefer the conformation in which the OH groups are quasi-diequatorial, and these are the most tumorigenic diol epoxides yet tested on mouse skin. 

An unusual regiocontrolled oxidation (epoxidation and dihydroxylation) of l-halo-1,3-dienes (equation 13) has been accomplished by use of potassium permanganate-MgSCU, after initial treatment with 2,2-dimethoxypropane78. The preferred epoxy diol is formed with the epoxide being adjacent to the chloro substituent. Further elaboration of these molecules yields highly sought after inositols with controlled stereochemistry. 

Diastereoselective epoxidations.6 Epoxidation of the ergoline 1 with m-chloro-perbenzoic acid provides the a-epoxide (2) with high diastereoselectivity and yield. In contrast, epoxidation via the bromohydrin provides the (1-oxide (2) in equally high diastereoselectivity. Osmylation of 1 also provides the 5a,6a-diol selectively (7 1) with similar preference for the a-face. 

The reaction of an epoxide with hydroxide ion leads to the same product as the acid-catalyzed opening of the epoxide a 1,2-diol (glycol), with anti stereochemistry. In fact, either the acid-catalyzed or base-catalyzed reaction may be used to open an epoxide, but the acid-catalyzed reaction takes place under milder conditions. Unless there is an acid-sensitive functional group present, the acid-catalyzed hydrolysis is preferred. 

Further exceptions to the "role of a-attack arise in the 5 -series, but the stereochemistry of reaction can be understood from an examination of the preferred conformation of the molecule. Reaction of the A, 5j5 0lefin (3) with reagents such as peracids and osmium tetroxide to give the epoxide and 2/ ,3jS-diol, respectively [6], clearly results from attack on the less-hindered face of the double bond, for the a face is shielded by ring B. In the analogous structure (4)... 

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