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Directed sequential synthesis of conjugated linoleic acid isomers from Δ 7, 9 to Δ 12, 14
Author(s) -
Destaillats Frédéric,
Angers Paul
Publication year - 2003
Publication title -
european journal of lipid science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.614
H-Index - 94
eISSN - 1438-9312
pISSN - 1438-7697
DOI - 10.1002/ejlt.200390004
Subject(s) - isomerization , conjugated linoleic acid , pericyclic reaction , double bond , cis–trans isomerism , chemistry , conjugated system , stereochemistry , linoleic acid , fatty acid , organic chemistry , catalysis , polymer
Position and configuration isomers of conjugated linoleic acid (CLA), from 7, 9‐ through 12, 14‐C18:2, were synthesized by directed sequential isomerizations of a mixture of rumenic ( cis ‐9, trans ‐11 C18:2) and trans ‐10, cis ‐12 C18:2 acids. Indeed, the synthesized conjugated fatty acids cover the range of unsaturated systems as found in milk fat CLA. The two‐step sequence consisted in initial sigmatropic rearrangement of cis/trans CLA isomers at 200 °C for 13 h under inert atmosphere (Helium, He), followed by selenium‐catalyzed geometrical isomerization of double bonds at 120 °C for 20 h under He. Product analysis was achieved by gas‐liquid chromatography using a 120 m polar capillary column coated with 70% cyanoalkylpolysiloxane equivalent polymer. Migration of conjugated systems was geometrically controlled as follows: the cis ‐C n , trans ‐C n+2 double bond system was rearranged through a pericyclic [1, 5] sigmatropic mechanism into a trans ‐C n‐1 , cis ‐C n+1 unsaturated system, while the trans ‐C n , cis ‐C n+2 double bond system was rearranged through a similar pericyclic mechanism into a cis ‐C n+1 , trans ‐C n+3 unsaturated system. Selenium‐catalyzed geometrical isomerization under mild conditions then allowed cis/trans double bond configuration transitions, resulting in the formation of all cis , all trans , cis‐trans and trans‐cis isomers. A sequential combination of the two reactions resulted in a facile controlled synthesis of CLA isomers, useful for the chromatographic identification of milk fat CLA, as well as for the preparation of CLA standard mixture.