Branched-Chain and Cyclic Fatty Acids

The Author: Gerhard Knothe, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL, USA.

Gunstone (1993) reported the 13C-NMR spectra of a large number of branched chain acids/esters differing in chain length (C6-C18) and in the nature and position of the branching group (methyl to hexadecyl). Some of the results are summarised in Table 1. Table 2 gives generalised data for mid-chain, iso, and anteiso acids/esters.

 

Table 1. Some chemical shifts (ppm) for 2-, 3-, and 4-methyl branched acids/esters
 C1C2C3C4C5C6methyl
 
2-methyl 18:0 A 183.67 39.47 33.59 27.20 nc nc 16.82
2-methyl 16:0 E 173.39 39.50 33.88 27.29 nc nc 17.08
3-methyl 16:0 E 173.77 41.70 30.39 36.78 26.96 nc 19.77
4-methyl 16:0 E 174.53 31.91 31.95 32.45 36.70 26.97 19.30

A = acid, E = ester, nc = not cited.

 

Table 2. Chemical shifts (ppm) at and close to branched methyl groups*
 CH3CHαβγα'β'γ'
 
mid-chain 19.7-19.8 32.9 37.2 27.1 30.1 37.2 27.1 30.1
iso 22.7 28.0 39.1 27.4 nc 22.7 na na
anteiso 19.3 34.5 36.7 27.2 30.1 nc 11.4 na
 
na = not applicable; nc = not cited.
* α, β, and γ refer to carbon atoms between the point of branching and the acid/ester function; α', β', and γ' refer to carbon atoms between the point of branching and the end methyl group.
 

 

Chemical shifts have been reported for the following acids and derivatives: 14-methyl 11c-15:1 (LePivert et al., 1995), 12-methyl-18:0 (Black, 1989), 11-methyl 12-18:1 (Carballeira et al., 1998), 2-methyl 20:0 (ethyl ester, Besra et al., 1993, 6-methyl 4t-24:1 (ethyl ester, Besra et al., 1993), 9,12-dimethyl-18:0 (Black, 1989), 2,4-dimethyl 14:0 (acid, methyl and ethyl ester, Wallace and Minnikin, 1996a), and 2,4,6-trimethyl 2-24:1 (Wallace and Minnikin, 1996b).

 

References

  • Besra, G.S., Minnikin, D.E.., Wheeler, P.R. and Ratledge, C. Synthesis of methyl (Z)- tetracos-5-enoate and ethyl (E)-6-methyltetracos-4-enoate: possible inhibitors in the biosynthesis of mycolic acid in mycobacteria. Chem. Phys. Lipids, 66, 23-34 (1993).
  • Black, K.D. Ph.D. Thesis, University of St. Andrews (Scotland) (1989).
  • Carballeira, N.M., Emiliano, A., Sostre, A., Restitoyo, J.A., Gonzalez, I.M., Colon,  G.M, Tosteson, C.G. and Tosteson, T.R. Fatty acid composition of bacteria associated with the toxic dinoflagellate Ostreopsis lenticularis and with the Carribean Palythoa species. Lipids, 33, 627-632 (1998).
  • Gunstone, F.D. High resolution 13C NMR study of synthetic branched-chain acids and of wool wax acids and isostearic acid. Chem. Phys. Lipids, 65, 155-163 (1993).
  • LePivert, M., Poisson, S., Laur, J., Coustille, J.-L. and Pages, X. Synthese d'un triglyceride d'acides gras ramifies de reference au niveau laboratoire et pilote. Oleagineux Corps gras Lipides, 2, 369-374 (1995).
  • Wallace, P.A. and Minnikin, D.E. Synthesis of racemic 2,4-dimethyltetradecenoic acid from Mycobacterium kansasii. Chem. Phys. Lipids, 82, 141-146 (1996a).
  • Wallace, P.A. and Minnikin, D.E. Synthesis of racemic 3-hydroxy-2,4,6-methyltetracosanoic (mycolipanolic) acid and racemic 2,4,6-trimethyltetracos-2-enoic (mycolipenic) acid. Chem. Phys. Lipids, 83, 1-8 (1996).

In This Section