The use of dimethyldioxirane as the epoxidizing agent for polyunsaturated fatty acids has been investigated. With fatty acid methyl esters this is a convenient method for avoiding acidic conditions, using different solvents, and simplifying the isolation procedures, with less contamination due to by-products. The reagent was also tested with free fatty acids in water. In this case, the supramolecular organization of fatty acids influenced the reaction outcome and the epoxidation showed interesting regioselective features. The double bonds closest to the aqueous-micelle interface is the most favored in the interaction with dimethyldioxirane. The preferential epoxidation of linoleic acid to the 9,10-monoepoxide was achieved, with a high yield and 65% regioselectivity. In case of arachidonic acid micelles, the regioselective outcome with formation of the four possible monoepoxide isomers was studied under different conditions. It resulted to be a convenient synthesis of cis-5,6-eicosatrienoic acid, whereas in reverse micelles epoxidation mostly gave cis-14,15-eicosatrienoic acid.
2006, Volume 89, Issue 10, 2243–2253