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Synthesis and isolation of trans-7, cis-9 octadecadienoic acid and other CLA isomers by base conjugation of partially hydrogenated γ-linolenic acid

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Lipids

Abstract

CLA is of considerable interest because of reported potentially beneficial effects in animal studies. CLA, while not yet unambiguously defined, is a mixture of octadecadienoic acids with conjugated double bonds. The major isomer in natural products is generally considered to be cis-9,trans-11-octadecadienoic acid (c9, t11), which represents >75% of the total CLA in most cases. Other isomers are drawing increased attention. The t7,c9 isomer, which is often the second-most prevalent CLA in natural products, has been reported to represent as much as 40% of total CLA in milk from cows fed a high-fat diet. The need for a reference material became apparent in a recent study directed specifically at measuring t7,c9-CLA in milk, plasma, and rumen. A suitable standard mixture was produced by stirring 0.5 g of γ-linolenic acid (all cis-6,9, 12-C18∶3) with 100 mL of 10% hydrazine hydrate in methanol for 2.5 h at 45°C. The solution was diluted with H2O and acidified with HCl. The resulting partially hydrogenated FA were extracted with ether/petroleum ether, dried with Na2SO4, and conjugated by adding of 6.6% KOH in ethlylene glycol and heating for 1.5 h at 150–160°C. Approximately 20 mg each of cis-6, trans-8; trans-7, cis-9; cis-9, trans-11; and rans-10, cis-12 were obtained along with other FA. Methyl esters (FAME) of these four cis/trans isomers were resolved by Ag+HPLC (UV 233) and partially resolved by GC/(MS or FID) (CP-Sil 88). Treatment of these FAME with I2 yielded all possible cis/trans (geometric) isomers for the four positions 6,8; 7,9; 9,11; and 10,12.

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Abbreviations

DMOX:

4,4′-dimethyloxazoline

GC-EIMS:

gas chromatography-electron ionization mass spectrometry

GLA:

γ-linolenic acid

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Authors and Affiliations

  1. University of Hamburg, Hamburg, Germany

    Lutz Lehmann

  2. Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, ONPLDS/DRAT, Room, 1E-009, HFS-840, 5100 Paint Branch Pkwy., 20740-3835, College Park, MD

    Pierluigi Delmonte, John A. G. Roach, Magdi M. Mossoba, K. M. Morehouse & Martin P. Yurawecz

Authors
  1. Pierluigi Delmonte
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  2. John A. G. Roach
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  3. Magdi M. Mossoba
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  4. K. M. Morehouse
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  5. Lutz Lehmann
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  6. Martin P. Yurawecz
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Correspondence to Martin P. Yurawecz.

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Delmonte, P., Roach, J.A.G., Mossoba, M.M. et al. Synthesis and isolation of trans-7, cis-9 octadecadienoic acid and other CLA isomers by base conjugation of partially hydrogenated γ-linolenic acid. Lipids 38, 579–583 (2003). https://doi.org/10.1007/s11745-003-1499-5

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  • DOI: https://doi.org/10.1007/s11745-003-1499-5

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