13C-NMR SPECTROSCOPY OF FATTY ACIDS AND DERIVATIVES
Branched Chain Acids
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. |
|||||||
| C1 | C2 | C3 | C4 | C5 | C6 | methyl | |
|---|---|---|---|---|---|---|---|
| 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*. |
||||||||
| CH3 | CH | α | β | γ | α' | 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), 12-methyl-18:0 (Black), 11-methyl 12-18:1 (Carballeira), 2-methyl 20:0 (ethyl ester, Besra), 6-methyl 4t-24:1 (ethyl ester, Besra), 9,12-dimethyl-18:0 (Black), 2,4-dimethyl 14:0 (acid, methyl and ethyl ester, Wallace), and 2,4,6-trimethyl 2-24:1 (Wallace).
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. PhD 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 (1996).
- 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).
The Scottish Crop Research Institute (MRS Lipid Analysis), Invergowrie, Dundee (DD2 5DA), Scotland
Updated: 20/1/2007 |
|
|
