Epoxidations with microorganisms

In connection with our own work on the enzyme-catalysed hydrolysis of cyclohexene epoxide with various fungi we made the unexpected observation that the microorganism Corynesporia casssiicola DSM 62475 was able to interconvert the (1R,2R) and (1S,2S) enantiomers of the product, trans cyclohexan-1,2-dioI 25. As the reaction proceeded the (1R,2R) enantiomer was converted to the (1S,2S) enantiomer [20]. If the racemic trans diol 25 was incubated with the growing fungus over 5 days, optically pure (> 99 % e. e.) (1 S,2S) diol 25 could be isolated in 85% yield. Similarly biotransformation of cis (meso) cycIohexan-1,2-diol 26 yielded the (1S,2S) diol 25 in 41 % (unoptimized) yield (Scheme 11). 

The conversion of the chromene 54 to epoxide 55 (a synthetic precursor for potassium channel modulators) and diol 56 (Fig. 40) may be achieved by a number of microbial catalysts, notably Mortierella rammaniana SC 13840 which gives the diol 56 in 65% yield m. 91% optical purity [62]. In an analogous conversion, the related microorganism Mortierella isabellina ATCC 42613 converted both chromenes 57 and 58 (Fig. 41) to a mixture of the corresponding cis- and tran -diols, presumably the result of regio- but nonstereo-selective acid-catalyzed hydrolysis of an intermediate epoxide, with both isomeric diols being formed in identical enantiomeric purities [34]. 

Microorganisms are able to form epoxides from several compounds with double bonds ... 

Incubations of heptachlor with a mixed culture of soil microorganisms for 12 weeks showed conversion of heptachlor to chlordene, 1-exohydroxychlordene, heptachlor epoxide, and chlordene epoxide. A mixed culture of soil microorganisms, obtained from a sandy loamy soil, degraded heptachlor epoxide to the less toxic 1-exohydroxychlordene. Conversion was about 1% per week during the 12-week test period (Miles et al. 1971). 

Bonding of chemicals to wood cell wall components--cellulose, hemicellulose and lignin—can change the physical and chemical properties of the wood. For example, reaction of southern pine with simple epoxides results in a modified wood which is resistant to attack by subterranean termites in laboratory tests (1). Wood modified with acetic anhydride, dimethyl sulfate, 0-propiolactone and epoxides are highly resistant to attack by microorganisms in standard soil block laboratory tests (2,3). Southern pine modified by reaction with acetic anhydride and propylene and butylene oxides has a reduced tendency to swell in the presence of water (4). 

In the environmental compartments, PCBs are degraded mainly hy microorganisms. Mono-, di-, and trichlorobiphenyls are broken down relatively quickly, whereas the more highly chlorinated PCBs are much more persistent. Highly chlorinated PCBs are reductively dechlorinated anaerobically with replacement of Cl by H, and the less-chlorinated products are subject to aerobic breakdown processes. The formation of ortho-dioh is thought to involve arene epoxides (Figure 11). 

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