Chiral epoxidations biosynthesis

The first enantioselective polyene tetracydization starting with a chiral epoxide was reported by Corey et al. in 1997 [8a]. The silylated enol ether 3 (Scheme 1) was converted into the tetracycle 4 by treatment with the Lewis acid MeAlCl2 at -90 °C. The synthetic route is modeled on the biosynthesis of lanosterol from (3S)-squalene 2,3-epoxide and has also been applied to the biomimetic synthesis of tetracyclic polyprenoids from sediment bacteria [8b]. 

Biosynthesis, This new section has been added because of the increased interest in enzymatic methods of ssmthesis of oxirans. Chiral epoxides may be produced from alkanes and alkenes by P. oleovorans thus oct-l-ene oxide (containing 10% (R)-iscmer) can be obtained from the parent alkene with a yield of 28mg cm" 83,84 ... 

We have seen that much detailed information is now available on the biosynthesis of plant sterols this includes the isolation of enzymes which form squalene epoxide and cyclize it to cycloartenol, elucidation of the pathways of alkylation leading to 24-alkyl sterols with opposite chirality at C-24, demonstration of the stereospecificity of reactions involving the A -> A -> A - A steps and desaturation of the side chain at C-22 and the removal of... 

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