A Facile and Efficient Method for the Synthesis of Labeled and Unlabeled Very Long Chain Polyunsaturated Fatty Acids

Several methods are available for elongation of fatty acid acyl chains. The present paper describes adaptation to the fatty acid field of a previously published protocol for manganese‐based Wurtz type coupling of alkyl bromides. 22‐Bromo‐3( Z ),6( Z ),9( Z ),12( Z ),15( Z ),18( Z )‐docosahexaene, easily prepared from 4( Z ),7( Z ),10( Z ),13( Z ),16( Z ),19( Z )‐docosahexaenoic acid, was coupled to homologous ω‐bromoesters by stirring for 4 hours at 40°C in the presence of manganese powder, a nickel catalyst and terpyridine. This afforded in yields of 70–75% a series of ω3‐hexaenoates of chain lengths of 32–40 carbons. The corresponding fatty acids of >98% purity were obtained following saponification and final purification. By using methyl [2,2,3,3,4,4‐ 2 H 6 ]10‐bromodecanoate as coupling partner it was possible to prepare a very long chain fatty acid in isotopically labeled form, i.e., [2,2,3,3,4,4‐ 2 H 6 ]14( Z ),17( Z ),20( Z ),23( Z ),26( Z ),29( Z )‐dotriacontahexaenoic acid. Also prepared were the monounsaturated long chain fatty acids 15( Z )‐octadecenoic acid and 15( Z )‐tetracosenoic acid. Very long chain fatty acids have been isolated from retina and other tissues and are of biological relevance. The methodology described will assist in further analytical and biological studies in this field.