Acids with conjugated unsaturation

Conjugated Dienes

The conjugated dienes attracting most attention are the so-called conjugated linoleic acids (CLA). These occur at low levels in the meat and milk fats of ruminant animals where they are produced by enzymic modification of linoleic acid in the rumen. They may also be produced by 9-desaturation of octadec-11-enoic acid. These acids show important physiological effects and are reported to inhibit tumour growth. Alkali-isomerization of linoleic acid also gives a mixture of 9c,11t and 10t,12c dienes with some other isomers as minor components. See our web page on the occurrence of conjugated fatty acids.

By whatever method CLA is produced, it is usually a complex mixture of positional isomers and of stereoisomers, and full analysis requires gas chromatography, silver ion chromatography, and mass spectrometry of appropriate derivatives. 13C-NMR has also been used to identify these mixtures and appropriate compounds have had to be synthesised or isolated. The best results are given by Lie Ken Jie et al. (1997) for all the 9,11 diene isomers and by Davis et al. (1999) for selected 8,10-, 9,11-, 10,12- and 11,13-isomers. Chemical shifts are given in Tables 1 and 2.

Table 1. Chemical shifts (ppm) for the four isomeric 9,11-18:2 acids (Lie Ken Jie et al., 1997)
 9c,11t9t,11c9t,11t9c,11c
1 174.32 174.34 174.22 174.27
2 34.10 34.10 34.09 34.10
3 24.95 24.95 24.98 24.97
4 29.06 28.97 29.04 29.14
5 - - - -
6 - - - -
8 27.66 32.06 32.61 27.46
9 129.89 134.51 132.16a 131.87c
10 128.71 125.72 130.37b 123.58d
11 125.58 128.57 130.51b 123.72d
12 134.76 130.17 132.43a 132.14c
13 32.92 27.72 32.68 27.54
14 29.41 29.73 29.40 29.68
15 28.95 28.97 28.97 29.04
16 31.77 31.77 31.82 31.81
17 22.65 22.65 22.68 22.69
18 14.12 14.12 14.13 14.13
abcd: These pairs may be interchanged.

 

Table 2. Chemical shifts (ppm) for isomeric 18:2 methyl esters (Davis et al., 1999).
 9c,11c9t,11t9c,11t11c,13t8t,10c10t,12c
1 179.98 179.86 180.09 180.09 180.05 180.09
2 34.06 34.00 34.05 34.06 34.03 34.06
3 24.68 24.67 24.67 24.69 24.63 24.67
4 - - 29.03 - - 29.06
5 - - 29.12 - - -
6 - - 29.03 - - -
7 29.57 29.36* 29.66 - 32.78 -
8 27.52 32.56 27.65 - 124.32 29.39
9 131.87 132.21 129.89 29.73 125.83 32.87
10 123.72 130.46 128.73 27.69 128.54 134.58
11 123.55 130.30 125.58 130.04 130.27 125.70
12 132.19 132.53 134.80 128.66 27.71 128.60
13 27.43 32.63 32.90 125.65 29.76 130.16
14 29.64 29.42* 29.40 134.66 - 27.68
16 31.76 31.77 31.76 31.59 31.87 31.50
17 22.64 22.63 22.63 22.29 22.68 22.57
18 14.09 14.10 14.10 13.95 14.12 14.06

 

Enynes

Reports are available for the chemical shifts for all carbon atoms in trans-octadec-11-en-9-ynoic acid and esters (also known as ximenynic or santalbic acid) and other acids/esters containing conjugated enyne systems (Table 3).

Table 3. Chemical shifts for acids/esters containing conjugated enyne systems
 (a)9a,11c-18:2*9a,11t-18:2*
  MethylGlycerol (α)Glycerol (β)MethylGlycerol (α)Glycerol (β)
1 174.32 174.27 173.179 172.771 174.31 173.142 172.774
2 34.10 34.074 33.997 34.142 34.074 33.974 34.138
3 24.85 24.917 24.806 24.840 24.921 24.806 24.837
4 28.81# 29.062 29.016 28.973 29.030 28.978 28.936
5 28.88#   28.893 28.874   28.814 28.842
6 30.07   28.817 28.805   28.783 28.710
7 142.96   28.691 28.691   28.786 28.786
8 109.50 19.542 19.500 19.500 19.329 19.324 19.324
9 92.66 94.277 94.224 94.193 88.547 88.444 88.418
10 84.90 77.561 77.482 77.489 79.287 79.304 79.319
11 109.76 109.30 109.300 109.300 107.76 109.826 109.826
12 144.58 142.67 142.618 142.602 143.45 143.296 143.306
13 33.26 30.040 30.031 30.031 32.980 32.998 32.998
14 28.72#   28.817 28.817   28.814 28.814
15 28.56#   28.691 28.691   28.710 28.710
16 31.74 31.706 31.701 31.701 31.690 31.697 31.697
17 22.67 22.645 22.636 22.636 22.614 22.617 22.617
18 14.16 14.119 14.130 14.130 14.103 13.103 13.103
(a) Heisteric acid 7c,9a,11t-18:3 (Spitzer et al., 1997).
*All chemical shifts are given to three decimal places - those with 6 digits are reduced to 5 in this Table (Lie Ken Jie et al., 1997).
#These shifts may be interchanged.

 

Conjugated Trienes and Tetraenes

The common natural acids of this type are C18 compounds with triene unsaturation at the 9,11,13 or 8,10,12 positions, and a 9,11,13,15-tetraene. These acids occur in several stereochemical forms. Chemical shifts for these compounds are listed in Table 4. Stellaheptaenoic acid (4c,7c,9t,11t,13t,16c,19c-22:7), isolated from a marine alga, contains the same conjugated tetra-ene unit as α-parinaric acid.

Newer results for α- and β-eleostearic, punicic, and catalpic acids, collected in Table 5, differ from the older data in Table 3. The newer information is obtained from oils containing these acids and chemical shifts are given for both α and β chains. However, there is poor agreement between these two sets of data. This is illustrated for α-eleostearic acid in Table 6 where olefinic signals and assignments are compared.

Table 4. Chemical shifts (ppm) for natural acids with conjugated triene (Gunstone, 1993) and tetra-ene (Spitzer et al., 1996,1997) systems [trivial names punicic (a), α-eleostearic (b), catalpic (c), β-eleostearic(d), jacaric (e), calendic (f), α-parinaric (g), stellaheptaenoic (h)]
 D-9,11,13D-8,10,12D-9,11,13,15D-4,7,9,11,13,
16,19
 ctccttttctttctcttccttcccttccc
  a b c d e f g h
5 nc nc nc nc 28.89 28.85 nc 128.98
6 nc nc nc nc nc nc nc 26.61
7 nc nc nc nc 27.81 32.78 nc 128.69
8 27.89 27.83 32.84 32.80 127.81# 126.21# 27.97 128.49
9 128.96 128.95 126.12# 130.73 128.07# 128.71# 132.83 127.33
10 132.38 132.91 128.79# 130.81 128.86# 130.85# 128.24 133.84
11 127.87 125.98 130.82# 134.19 129.07# 132.04# 128.14 133.86
12 128.02 134.90 131.75# 133.98 132.09# 132.71# 132.88 128.52
13 132.62 131.52 132.77# 130.95 132.57# 134.66# 132.91 129.19
14 128.86 130.73 134.70# 130.60 27.89 27.89 128.21 132.18
15 27.65 32.53 27.58 32.53 nc nc 128.89 26.61
16 31.94 31.58 31.95 31.58 31.57 31.56 134.52 130.37
17 22.39 22.28 22.38 22.28 22.62 22.62 21.33 129.51
18 14.02 13.95 14.00 13.95 14.10 14.11 14.37 26.61*

 

Table 5. Chemical shifts (ppm) for natural acids with conjugated triene systems (Blaise et al., 1997)
 A/αA/βB/αB/βC/αC/β
9 131.724 131.685 134.184 134.142 128.937 128.920
10 128.837 128.818 130.631 130.613 132.426
11 125.986 125.965 130.798 130.782 127.858 127.840
12 132.926 132.906 130.963 130.942 128.025
13 130.640 130.631 130.505 132.688 132.668
14 135.164 135.141 134.444 134.426 - -

(A) α-Eleostearic, (B) β-eleostearic, (C), punicic.
Also, catalpic glycerol esters 134.897 (α), 132.760 (α), 131,973 (β), 131,957
(α), 128,715 (α and β), 126.148 (β), 126.132 (α), 130.755 (β), 130.741 (α).
- These chemical shifts are not assigned to individual carbon atoms and it is not clear why 9 values are listed.

 

Table 6. Chemical shifts (ppm) listed in increasing numerical value for olefinic carbon atoms in α-eleostearic acid according to Tulloch and Blaise
Tulloch and Bergter (1979)Blaise et al. (1997)
Shift (ppm)Carbon atomShift (ppm)Carbon atom
125.98 11 125.99 11
128.95 9 128.84 10
130.73 14 130.64 13
131.52 13 131.72 9
134.90 12 135.16 14

 

References

  • Blaise, P., Wolff, R. and Farines, M.  Etude regiospecific de triacyglycerols d'huiles vegetales par clivage chimique et RMN 13C haute resolution, Oleagineux Corps gras Lipides, 4, 135-141 (1997).
  • Davis, A.L., McNeill, G.P. and Caswell, D.C. Analysis of conjugated linoleic acid isomers by 13C-NMR spectroscopy. Chem. Phys. Lipids, 97, 155-165 (1999).
  • Gunstone, F.D. High resolution 13C-NMR spectroscopy of lipids. In: Advances in Lipid Methodology - Two, pp. 1-68 (ed. W.W. Christie, Oily Press, Dundee) (1993).
  • Lie Ken Jie, M.S.F., Pasha, M.K. and Ahmad, F. Ultrasound-assisted synthesis of santalbic acid and a study of triacylglycerol species in Santalum album (Linn.) seed oil. Lipids, 31, 1083-1089 (1996).
  • Lie Ken Jie, M.S.F., Pasha, M.K. and Ahmad, F. Synthesis and nuclear magnetic resonance properties of all geometrical isomers of conjugated linoleic acids. Lipids, 32, 1041-1044 (1997).
  • Mikhailova, M.V., Bemis, D.L., Wise, M.L., Gerwick, W.H., Norris, J.N. and Jacobs, R.S. Structure and biosynthesis of novel conjugated polyene fatty acids from the marine green alga Anadyomene stellata, Lipids, 30, 583-589 (1995).
  • Spitzer, V., Tomberg, W., Hartmann, R. and Aichholz, R. Analysis of the seed oil of Heisteria silvanii (Olacaceae) - a rich source of a novel C18 acetylenic fatty acid, Lipids, 32, 1189-1200 (1997).
  • Spitzer, V., Tomberg, W. and Zucolotto, M. Identification of α-parinaric acid in the seed oil of Sebastiana brasiliensis Sprengel (Euphorbiaceae). J. Am. Oil Chem. Soc., 73, 569-573 (1996).
  • Tulloch, A.P. and Bergter, L. Analysis of the conjugated triene acid containing oil from Fevillea trilobata by 13C nuclear magnetic resonance spectroscopy. Lipids, 14, 996-1002 (1979).

Updated: January 22, 2007